Viewing Jupiter from Earth

Jupiter's the 3rd brightest object in the night sky (after the moon and Venus). Jupiter contains atmospheric bands visible from Earth. Jupiter has many moons that vary in properties. The four largest are the Galilean moons and are visible from Earth with even a small telescope.

Saturn was the most distant planet known to ancient Greek astronomers. Saturn orbits at nearly twice Jupiter's distance from the sun (which makes it considerably fainter than Jupiter or Mars as viewed from Earth). Saturn also contains atmospheric bands, but they are less distinct than Jupiter's. Saturn has an overall butterscotch hue. Saturn also has many moons orbiting it. Saturn's best known feature - its ring system.

Discovered by British astronomer William Herschel in 1781. Under the best possible conditions, Uranus is just barely visible to the naked eye. Through a large telescope, it appears as a tiny, pale greenish disk. From observing Uranus's orbital motion, it was determined that another planet must be out beyond it as they had trouble fitting an elliptical orbit to the path of Uranus that could accurately predict its position. Introducing another planet into the mix fixed this discrepancy.

In 1846, German astronomer Johann Galle found Neptune nearly where it was predicted to be. Its mass and orbit were both determined by John Adams (English mathematician) and Urbain Leverrier (French mathematician) independently using Uranus's orbital data. Neptune cannot be seen with the naked eye. Through a large telescope, appears as a small bluish disk. A few markings (cloud bands) can be seen only under the best conditions. From Voyager 2, Neptune appears to have atmospheric bands and spots, like a blue-tinted Jupiter.

Large masses, large radii, low average densities. Saturn is less dense than water - it would float! Jovian planets are large enough that their gravity can hold on even to the light gases - predominantly composed of hydrogen and helium. Each has a dense, compact core at the center more massive than Earth. Jupiter, Saturn, and Neptune have significant internal heating. None of the jovian planets has a solid surface of any kind - the gases just get denser and hotter the further down you go (eventually becoming a liquid, which defines the "surface").

Lack of solid surface leads to differential rotation - the rotation rate is not constant from one location to the next. On Jupiter, the poles rotate slower by about 6 minutes as compared to the equatorial regions. On Saturn, the difference is 26 minutes, again slower at the poles. Difference is even more marked on Neptune. On Uranus, the difference is more than 2 hours, with the poles moving faster. Differential rotation observed in the surface layers reflects large-scale wind flows in the planets' atmospheres. There is no clear relationship between the interior and atmospheric rotation rates - one can move faster than the other and it varies between the 4 planets. The rotation axis of most planets is nearly perpendicular to the ecliptic plane (the plane in which the solar system mainly lies). Uranus however has its rotation axis nearly parallel to the plane.

Appearance dominated by colorful atmospheric cloud bands arranged parallel to the equator and an oval atmospheric blob called the "Great Red Spot." The Great Red Spot in the long direction is nearly twice Earth's diameter and seems to be a hurricane that has persisted for hundreds of years. Atmospheric composition: 86% hydrogen 14% helium Small amounts of atmospheric methane, ammonia, and water vapor. Complex chemical processes occurring in Jupiter's atmosphere are responsible for the colors that we see. Banded cloud structures: Zones - lighter colored Belts - darker colored The zones and belts vary in position and intensity with time, and are the result of convective motion in the atmosphere. Zones - high-pressure areas moving upward. Belts - low-pressure areas moving downward. However, Cassini observations conflict with the above stated standard view. ones and belts are equivalent to low and high pressure systems we experience on Earth. Due to Jupiter's rapid differential rotation, these systems wrap completely around the planet. Because of the pressure difference, belts and zones lie at slightly different heights in the atmosphere, and thus have slightly different temperatures. This temperature difference is responsible for the difference in colors between the two regions. Zonal flow - underlying the bands is a very stable pattern of eastward and westward wind flow. The equatorial regions of the atmosphere rotate the fastest, at a rate of 500 km/h, similar to the jet stream on Earth. At higher latitudes, there are alternating regions of eastward and westward flow, corresponding to the pattern of zones and belts. Near the poles, where the zonal flow disappears, the band structure vanishes also.

White ammonia clouds generally lay over the colored layers. Above the ammonia clouds lies a thin, faint layer of haze created by chemical reactions similar to those on Earth that cause smog. Since it lacks a solid surface, the zero point is taken to be the top of the troposphere (the turbulent region where the clouds lie that we see). As on other planets, weather on Jupiter is the result of convection in the troposphere. Above the troposphere, the temperature rises as the atmosphere absorbs solar UV light. Below the haze layer, at -30 km, lie white, wispy clouds of ammonia ice at a temperature of 125 to 150 K. A few tens of km below the ice, the temperature is above 200 K and we have clouds of ammonium hydrosulfide. Even deeper, we have clouds of water ice or water vapor. The top of the deepest cloud layer, which is not visible to us, lies 80 km below the troposphere. In 1995, Galileo probe arrived at Jupiter. Galileo survived in the atmosphere for about an hour before being crushed by atmospheric pressure at an altitude of 150 km below the troposphere. Galileo's findings are consistent with the picture we just described.

n addition to the large-scale zonal flow, Jupiter experiences many smaller-scale weather patterns. The Great Red Spot is one example. The center remains tranquil in appearance, like the eye of a hurricane. This storm resembles a hurricane in that it rotates. The storm has persisted for at least 300 years. Also many smaller circulating storms that appear as white ovals. Brown ovals are holes in the overlying clouds that allow us to see down into the lower atmosphere. Storms are localized anomalies in the zonal flow. Storms survive on Jupiter if the they are large enough to not be affected by other storms. On Earth, storms (hurricanes) die out once they reach land as this interrupts their flow of energy. Jupiter has no land, thus no interruptions to the storms.

Not as much atmospheric structure as Jupiter. Yellowish and tan cloud bands that parallel the equator. Storms do exist, but there's largely no difference in color between them and the cloud bands. Composition: 92.4% Hydrogen 7.4% Helium Traces of methane and ammonia Much less helium than on Jupiter - believe Saturn's helium liquefied at some point and sank toward the center of the planet. Very similar to Jupiter's, just lower temperatures due to increased distance from the sun. Troposphere contains clouds arranged in 3 distinct layers composed of (in order of increasing depth) ammonia ice, ammonium hydrosulfide ice, and water ice. Above the clouds, there is a layer of haze. Total thickness of the 3 cloud layers is about 3 times the thickness on Jupiter due to Saturn's weaker gravity (Jupiter pulls much harder on its cloud layer). Saturn's yellow color is likely due to the same photochemistry as on Jupiter, but on Saturn we only see the less colorful top layer (remember holes in Jupiter's top layer lets us see below).

Computer enhanced images of Saturn show the presence of bands, oval storm systems, and turbulent flow patterns. Stable east-west zonal flow, greater wind speed (1500 km/h) than on Jupiter and fewer east-west alternations than on Jupiter. "Dragon Storm" thought to be similar to a thunderstorm on Earth. Millions of times stronger than we've experienced here on Earth, but does contain lightning and water and ammonia rain. Thought to be a long-lived phenomena that occasionally flares up.

Very similar to that of Jupiter. Molecular hydrogen (84%) Helium (14%) Methane 3% on Neptune 2% on Uranus Ammonia not observed in any significant amount (probably exists in the form of ice crystals due to low atmospheric temperatures). Blue color of outer jovian planets is due to the relatively high presence of methane. Methane is quite efficient at absorbing red light, so mostly blue light is reflected by the planets (deeper blue means more methane).

Few clouds exist in Uranus's cold upper atmosphere. This means we must look deeper into the atmosphere to see structures (bands and spots) which characterize the flow patterns like on the other jovian planets. Stratospheric haze also washes out any of the structure that would be visible below it. Uranus's atmospheric clouds and flow patterns move around the planet in the same direction as its rotation, with wind speeds from 200 to 500 km/h.

Neptune's upper atmosphere is hotter than Uranus's due to internal heating. Extra warmth makes the haze thinner and clouds higher, so its easier to see. Among the main cloud tops, there are white methane clouds. Equatorial winds blow east to west at speeds over 2000 km/h. Interior rotates west to east. No explanation for the winds behavior. Largest storm - "Great Dark Spot" - akin to Jupiter's Great Red Spot. Comparable in size to Earth. However, it has since disappeared and new storms similar to it have formed.

Based on models that best fit the observed data (have never explored the interiors of the jovian planets!). Temperature and pressure increase with depth. Gas gradually turns to liquid, and even deeper the liquid hydrogen enters a liquid metallic state (excellent conductor of electricity like other metals). Jupiter is flattened - bulges at the equator. This implies a dense core having a mass 10 times the mass of Earth. Believe the core is molten or semi-solid rock. Enormous central pressure (50 million times that on Earth's surface) compresses the core to no more than 20,000 km in diameter.

Same basic internal parts as Jupiter, but in different proportions. Metallic hydrogen layer is thinner, central dense core is larger (about 15 Earth masses). Due to lower mass, core temperature is less extreme, as are core density and pressure. Central pressure is 1/10 that of Jupiter (not too different from that of Earth).

Low enough interior pressures that hydrogen stays in molecular form all the way to the cores. May have high-density "slushy" interiors below the clouds composed of highly compressed water clouds. Also possible that much of the ammonia is dissolved in the water clouds, producing a thick electrically conducting layer. From their relatively large densities, it is assumed that they have Earth-sized cores that are similar in composition to those of Saturn and Jupiter.

Jupiter has strongest magnetic field in the solar system. All four Galilean moons lie within Jupiter's magnetosphere. Jupiter experiences aurorae that are larger and more energetic than those on Earth. Saturn also has a strong magnetic field, however it is only 1/20 that of Jupiter's due to the lower level of metallic hydrogen. Saturn's magnetosphere contains the planet's ring system and most of its moons. Uranus and Neptune also have strong magnetic fields (a few % of Saturn's, 30 to 40 times that of Earth). Uranus and Neptune's magnetic fields are not aligned with the planets' rotation axes and are offset from the planets' centers - no idea why.

Jupiter emits about twice as much energy as reaches the planet in the form of sunlight. Excess heat emission from Jupiter is likely here from its formation which is still leaving the planet today - it is still cooling. Saturn emits about three times as much energy as reaches the planet in the form of sunlight. Since Saturn is smaller than Jupiter, the heat from its formation must have left it long ago. On Jupiter, liquid helium dissolves in liquid hydrogen due to the high temperatures. This doesn't happen on Saturn. On Saturn, helium condensed in the clouds and it has been raining helium ever since. As the helium sinks toward the center of the planet, gravity compresses it and heats it up. The energy released in this process is the source of Saturn's internal heating. Eventually, the process will cease and Saturn will cool. Uranus has no internal heating - it emits exactly what it absorbs from the sun. Neptune does have internal heating, but we don't know its source. Possible that the high concentration of methane insulates the planet, helping it maintain its initially high internal temperature (didn't allow the planet to cool as much).

Four large moons travel on nearly circular, prograde orbits in Jupiter's equatorial plane. Moving outward from the planet, they are Io, Europa, Ganymede, and Callisto. Like a miniature solar system, their densities decrease with increasing distance from Jupiter. Io and Europa have large, iron-rich cores surrounded by thick mantles of rocky composition. Europa has a water / ice outer shell between 100 and 200 km thick. Ganymede and Callisto are of more lightweight overall composition (low-density materials like water ice). Ganymede has a small metallic core topped by a rocky mantle and a thick icy outer shell. Callisto is an undifferentiated mixture of rock and ice.

Most geologically active object in entire solar system. Similar to Earth's moon in mass and size. Uncratered surface is collage of oranges, yellows, and blackish browns. Has active volcanoes. Io's smooth surface is apparently the result of molten matter constantly filling in any dents or cracks. Thin atmosphere made up mainly of sulfur dioxide, produced by volcanic activity and temporarily retained by the moon's gravity. More than 80 active volcanoes have been identified on Io. Largest volcano, named Loki, is larger than the state of Maryland and emits more energy than all of Earth's volcanoes combined. Io is too small to have all of this activity - it should have died long ago like our moon. The source of Io's energy is external - Jupiter's gravity, combined with that of the other moons. If no other moons were present, it would have suffered the same fate as our moon. Due to the gravity of the other moons, Io is constantly "pulled" back and forth creating tidal stresses that continually flex and squeeze the interior. The large amount of heat generated within Io causes huge jets of gas and molten rock to squirt out of the surface. Likely much of the interior is soft or molten, with only a relatively thin solid crust overlying it.

Relatively few craters on its surface. Surface displays vast network of lines crisscrossing bright, clear fields of water ice. Ice may be several km thick, with oceans below up to 100 km deep. Again Jupiter's gravity and the pull of the other moons is the source of energy, but the effects here are less extreme due to increased distance from the planet. Icy equivalent of lava flows on Earth - water erupted through the surface and flowed for many km before solidifying (also called ice volcanism). Has a weak magnetic field that constantly changes strength and direction (direct evidence for the saltwater ocean, which would conduct electricity and thus establish a magnetic field). May contain more liquid water than exists on Earth. While still a hostile environment, the large presence of water oceans presents the possibility of life forming on Europa.

Ganymede is largest moon in solar system, also larger than both Mercury and Pluto. Darker regions on Ganymede are original icy surface, heavily cratered. Lighter regions are smoother - liquid water upwelled from the interior, flooding the impact regions before solidifying. Ganymede has a system of grooves and ridges indicative of plate tectonics occurring in the moon's past - ceased 3 billion years ago as the crust became too thick. Callisto is more heavily cratered with fewer fault lines than Ganymede. Callisto's most obvious feature - series of concentric rings surrounding two large basins. Formed from an impact - upthrust ice partially melted and solidified before ripples subsided. Callisto froze before plate tectonics or other activity could start. From cratering rate, Callisto's surface is maybe 4 billion years old. Ganymede's differentiation indicates it was largely molten at some point, while Callisto is undifferentiated and apparently never molten. Ganymede has a weak magnetic field, suggesting the presence of a liquid or "slushy" water below its surface. Can't yet explain all the features of these moons.

Largest moon of Saturn. Orange color comes from presence of an atmosphere. A thick, uniform haze layer completely covers the moon. Surface has icy plateaus smeared with hydrocarbon tar. Ridges and cracks on surface suggest geological activity in the form of "titanquakes" may be common. Evidence for some sort of erosion occurring (possibly wind or volcanic activity). Fewer craters than expected also suggests geological activity (resurfacing is occurring). Atmosphere is thicker and denser than Earth's and more substantial than any other moon. Atmospheric composition: 90% Nitrogen Up to 10% Argon Few % Methane Trace amounts of other gases. Surface temperature is a frigid 94 K. Water ice plays the role of rock on Earth, and liquid water the role of lava (as on Ganymede and Callisto). At the temperatures typical of the lower atmosphere, methane and ethane behave rather like water on Earth - possibly methane rain, snow, fog, and even rivers and oceans. Atmosphere acts like a gigantic chemical factory. Scientists are interested in it as the same reactions may have preceded the existence of life on Earth. These reactions would have been necessary for Earth to have been hospitable for life. Huygens probe in 2005 entered Titan's atmosphere - images show a network of drainage channels leading to a shoreline. It landed on solid ground and transmitted images for an hour. Titan's low temperature allows it to retain an atmosphere easier than other moons like Ganymede and Callisto. Don't yet know if Titan's differentiated or not.

Neptune's large moon, about half the mass of Europa. Icy surface that reflects much of the sunlight reaching it - temperature of only 37 K. Thin nitrogen atmosphere and solid frozen surface probably composed of water ice. Nitrogen frost forms and evaporates seasonally over the polar caps. Surface activity has erased most of the impact craters. Large fissures on the surface (like Ganymede). Numerous frozen lakes of water ice, thought to be volcanic in origin. Voyager 2 detected great jets of nitrogen gas erupting several km into the sky. Scientists speculate such nitrogen geysers on Titan are common and perhaps responsible for the thin atmosphere. Triton is the only large moon in the solar system to orbit its planet in retrograde. Only large jovian moon to not orbit in the parent planet's equatorial plane (i.e. orbit is tilted compared to others). Due to odd orbital behavior, it is thought that Triton was captured by Neptune rather than forming along with Neptune. Triton is spiraling in towards Neptune due to retrograde orbit. (Our moon is slowly spiraling away from Earth.) Triton is doomed to be torn apart by Neptune's gravitational field, probably within 100 million years due to its inward motion.

Most show no signs of significant geological activity, with a few exceptions. Saturn's Dione has bright ice cliffs created by tectonic fractures - surface cracked and buckled as moon cooled. Ice volcanism appears to have erased older craters. Saturn's Iapetus has a two-faced appearance - one hemisphere is very dark and the other very light. Don't know if dark material is coming from inside or outside the moon. Saturn's Tethys and Uranus's Ariel both have extensive cracks on their surfaces, which are most likely the result of meteoritic bombardment. Saturn's Enceladus has ongoing geological activity - possibly coated with ice crystals, the result of water volcanoes. Much of surface is devoid of craters, which would have been erased by "lava flows" of water liquefied during internal upheavals and now again frozen. Don't know why such a small moon has so much activity. Radii between 200 and 800 km. Densities suggest that all are composed mostly of rock and water ice. All move on nearly circular orbits and are tidally locked by their parent planet's gravity into synchronous rotation. Most show heavy cratering. Saturn's Mimas and Uranus's Miranda show clear evidence of violent meteoritic impacts. The impact that caused the large crater on Mimas must have come very close to shattering the moon. Some speculate Miranda's varied terrains are the result of multiple major impacts, with the pieces falling back together in a chaotic, jumbled way.

All four jovian planets have ring systems girdling their equators. Many of the inner jovian moons orbit close to (or even within) the parent planet's rings. Saturn's rings are the best known and best observed, and we will describe them in detail.

Features: Cassini Division - dark gap about 2/3 way out from inner edge. A ring - outside the Cassini Division. Inner rings - B and C rings. B ring is the brightest. C ring is almost translucent. Encke gap - smaller division located in the outer part of the A ring. Additional rings (D, E, and F) cannot be seen in image. Rings lie in Saturn's equatorial plane. Since Saturn's rotation axis is tilted, the appearance of the rings changes seasonally (depending on how the sunlight illuminates them). The rings are very thin - thickness is less than a few hundred meters even though they are more than 200,000 km in diameter. Rings are not solid objects. Composed of many small solid particles orbiting the planet, like many tiny moons. High reflectivity of rings suggests the particles are made of ice, with small rocky particles and dust mixed in. Particles range in size from fractions of a millimeter to tens of meters in diameter. Most particles are the size (and composition) of a large and dirty snowball.

Consider the fate of a small moon orbiting close to a massive planet. As the moon gets closer, tidal forces increase, stretching the moon along the direction to the planet. Eventually, the moon is pulled apart by the planet's gravity. The pieces of the satellite move on their own individual orbits around that planet, and eventually spread all the way around forming a ring. The Roche limit is the critical distance from the parent planet, inside of which a moon will be destroyed. For Saturn, the Roche limit lies 150,000 km from the planet's center, just outside the outer edge of the A ring. All ring systems are found within the parent planet's Roche limit. These arguments apply only to objects held together by self-gravity (e.g. this doesn't apply to artificial satellites that are held together by interatomic forces).

Saturn's main rings are composed of thousands of narrow ringlets. This structure varies with both time and position in the rings. Ringlets are formed when the mutual gravitational attraction of the ring particles creates waves of matter, regions of high and low density, that move in the plane of the rings like ripples on the surface of a pond. Narrower gaps in the rings (about 20) are swept clean by action of small moonlets embedded in them. The moonlets (10 or 20 km across) are larger than the particles and sweep up ring material as they go. Largest gap, the Cassini Division, has a different origin - the gravitational influence of the inner-most medium-sized moon Mimas. Its gravity has kicked out particles that once lied in the Division.

Jupiter's ring system lies 50,000 km above the top cloud layer, inside the orbit of the innermost moon. Composed of dark fragments of rock and dust chipped off the inner moons by meteorites. A few tens of km thick.

Uranus's ring system consists of 11 thin rings and is too faint to detect directly. Dark, narrow, and widely spaced. Less than a few tens of meters thick. Shepherd satellites exist that keep their positions in place.

Neptune is surrounded by 4 dark rings. 3 are quite narrow like Uranus's, while 1 is quite broad and diffuse like Jupiter's. Outermost ring is noticeably clumped in places. No connection yet established between the small inner satellites and the rings, although clumping may be caused by shepherd satellites.

Believe the rings are quite young (no more than 50 million years old) due to their dynamic behavior (waves, collisions, and interactions with moons). If they are young, perhaps they are replenished from time to time (fragments broken off of inner moons by impacts, or a moon recently torn apart by tidal forces or destroyed in an impact with another object). Total mass of Saturn's rings is enough to make a satellite about 250 km in diameter. Neptune's large moon Triton will likely be destroyed once it crosses the Roche limit and will form into a ring system (within the next 100 million years). By then Saturn's ring system could have disappeared and Neptune would be known for the great ring system.

Observations of Uranus's and Neptune's orbits led to the conclusion that there must be another object out there (similar to what led to the discovery of Neptune). Percival Lowell attempted to find the 9th planet, but it was Clyde Tombaugh who found it while working at Lowell Observatory, 6 degrees away from where Lowell predicted it would be. Well, the supposed irregularities in Uranus's and Neptune's orbits don't actually exist, and Pluto's not massive enough to have caused them anyway. At nearly 40 AU from the sun, Pluto is hard to distinguish from the background stars. Never visible to the naked eye (like Neptune). Only "planet" not studied at close range by NASA spacecraft (new mission should be there by 2015 though). Above image taken with the Hubble Space Telescope. Only surface features to be conclusively identified are the bright polar caps. Some of the dark regions may be craters or impact basins.

Pluto's satellite, Charon, was discovered in 1978. Based on Charon's orbit, Pluto's mass has been determined to be about 0.0021 Earth masses, or 0.17 times the mass of Earth's moon. Charon's mass is about 0.12 that of Pluto, giving the Pluto-Charon system the largest satellite-to-planet mass ratio in the solar system. Pluto's radius is 1150 km (1/5 Earth's) and Charon's is 600 km. Pluto and Charon are tidally locked as they orbit each other. Pluto is the 3rd planet in the solar system to have retrograde rotation. 2 candidate moons were found in 2005 using HST, each about 100 to 200 km in diameter.

Mass, radius, and density are what we'd expect of an icy moon of a jovian planet. Similarities to Triton (Neptune's large moon) stem from the fact that both probably formed in the Kuiper belt. Many Pluto-sized objects existed in the early system, Pluto is simply the largest surviving member of the class. Charon was captured by Pluto late in the formation process, following either a collision or near-miss between the two (reminiscent of the formation of Earth's moon).

Asteroids, meteoroids, comets: any small body in the solar system. Important as they offer information about the early solar system. The early solar system cannot generally be investigated using the planets as the planets have evolved over time (e.g. geologic activity on Earth, etc.)

Asteroids - fragments of rocky material larger than 100 m in diameter. Vast majority found in the "asteroid belt," located between Mars and Jupiter. All but one orbit the sun in prograde orbits (in same direction as the planets). Trojan asteroids - locked in place in Jupiter's orbit due to the balance of Jupiter and the sun's gravitational forces. Asteroids can be deflected into the inner solar system by the gravitational field of Mars or Jupiter - can cross Earth's orbit. More than 3300 Earth-crossing asteroids are known. Most will eventually collide with Earth.

Can estimate size by the amount of sunlight they reflect and the heat they radiate. Total mass of all asteroids probably amounts to less than 1/10 the mass of our moon. Asteroid compositions are inferred from spectroscopic observations. Darkest (least reflective) asteroids contain water ice and organic (carbon-rich) compounds - called carbonaceous asteroids. More common overall and increase in number as you move further out in the solar system. The more reflective silicate asteroids are composed primarily of rocky material. More common in the inner solar system. The asteroid Ida has a small moon (Dactyl) which orbits it. Some asteroids (like Mathilde) are porous, meaning they are not solid rock.

Comets - icy rather than rocky in composition and typical diameters range from 1 to 10 km. Travel in highly elliptical orbits about the Sun. Tails form when comets near the sun (composed of dust or ionized gas). Nucleus - main solid body of a comet - only a few km in diameter. Coma - forms when comet comes within a few AU of the sun as part of the icy surface becomes gaseous and evaporates forming a cloud around the nucleus. Tail is largest part, coma is brightest part, and nucleus is more massive part. Tails are directed away from the sun by the solar wind (an invisible stream of matter and radiation escaping from the sun). Most famous comet - Halley's comet, which appears once every 76 years (most recently in 1986). Comets are often called dirty snowballs (nucleus contains rocky material and ice, as well as methane, ammonia, and carbon dioxide).

Highly elliptical orbits take them far beyond Pluto, where they spend most of their time. Not confined to a few degrees within the ecliptic, unlike the other objects in the solar system. Roughly uniformly distributed in all directions from the sun. Short-period comets originate from the Kuiper belt, where either comet-comet interactions or the gravity of Neptune kicks them into an orbit which brings them to the inner solar system. Comets that lie outside of Pluto's orbit form the Oort cloud, which completely surrounds the sun. Oort cloud may be up to 100,000 AU in diameter. Oort cloud members rarely venture into the main solar system (closer than Pluto). Since the Oort cloud exists in all directions (rather than in just the plane of the ecliptic), objects originating from there come from all directions (unlike objects from the Kuiper belt).

Meteoroids - fragments of rocky material less than 100 m in diameter. Meteor - sudden streak of light in the night sky caused by friction between air molecules in Earth's atmosphere and an incoming piece of asteroid, meteoroid, or comet. Meteorite - any piece of interplanetary debris that survives its fiery passage through our atmosphere and finds its way to the ground. Smallest meteoroids are rocky remains of broken-up comets - called micrometeoroids. The comet fragments initially travel in a tightly knit group called a "meteoroid swarm" moving in nearly the same direction as the parent comet. A meteor shower results when Earth's orbit intersects the orbit of such a young cluster of meteoroids. Meteor showers are named for the constellation from which they appear to originate. Larger meteoroids (more than a few cm in diameter) are not usually associated with comets. Larger meteoroids are more likely small bodies that have strayed from the asteroid belt. Larger meteoroids are responsible for most of the cratering on the surfaces of the moon, Mercury, Venus, and Mars. A few meteorites have been identified as originating from the moon or Mars, having been blasted off by some impact on those bodies. Meteoroids less than about 1 m across burn up in Earth's atmosphere. Larger meteoroids reach the surface, where they can cause significant damage. Major collisions between Earth and large meteoroids are thought to now be rare, occurring on average once every few hundred thousand years. One of the most recent large impacts was in 1908 in Siberia (meteoroid was 30 m across - equal to a 10-megaton nuclear detonation). Most meteoroids are rocky, although a few are composed of iron and nickel. Almost all meteorites are old. Radioactive dating shows most to be between 4.43 and 4.6 billion years old.

Each planet is relatively isolated in space. The orbits of the planets are nearly circular. The orbits of the planets all lie in nearly the same plane. The direction in which the planets orbit the sun (counterclockwise as viewed from above Earth's north pole) is the same as the direction which the sun rotates on its axis. The direction in which most planets rotate on their axis is roughly the same as the direction in which the sun rotates on its axis (not Venus, Uranus, and Pluto). Each planet is relatively isolated in space. The orbits of the planets are nearly circular. The orbits of the planets all lie in nearly the same plane. The direction in which the planets orbit the sun (counterclockwise as viewed from above Earth's north pole) is the same as the direction which the sun rotates on its axis. The direction in which most planets rotate on their axis is roughly the same as the direction in which the sun rotates on its axis (not Venus, Uranus, and Pluto). The direction in which most of the known moons revolve about their parent planet is the same as the direction in which the planet rotates on its axis. Our planetary system is highly differentiated (terrestrial and jovian planets). Asteroids are very old and exhibit a range of properties not characteristic of either the terrestrial or the jovian planets or their moons. The Kuiper belt is a collection of asteroid-sized icy bodies orbiting beyond Neptune. The Oort cloud comets are primitive, icy fragments that do not orbit in the plane of the ecliptic and reside primarily at large distances from the sun.

Cloud of interstellar dust and gas - a nebula, begins to contract (for whatever reason) under its own gravity. As it contracts, it becomes denser and hotter, eventually forming a star at its center. As it contracts, the cloud spins faster and faster forming a flattened pancake-shaped disk (due to angular momentum). The flattened-pancake is usually referred to as the solar nebula since it will form our solar system. The idea that planets form from such a disk is called the "nebular theory." We have seen such disks formed in other systems. The old nebular theory is wrong as we now know clumps of matter would not form from the gas as they would have dispersed and not formed planets.

The current theory, condensation theory, is built on the nebular theory. Key ingredient - interstellar dust in the solar nebula. The dust acts as condensation nuclei (microscopic platforms to which other atoms can attach) and helps the cloud cool enough for condensation to occur in the first place

According to condensation theory, the planets formed in 3 distinct stages. First 2 apply to all planets, 3rd applies only to the Jovian worlds. Stage one Dust grains in the solar nebula formed condensation nuclei. These clumps then stick to other clumps, causing the clumps to grow in size rapidly. The process of accretion (gradual growth of objects by collision and sticking) created objects a few hundred km across. At the end of the first stage, solar system consisted of hydrogen and helium gas and millions of planetesimals (objects size of small moons having gravitational fields just strong enough to affect their neighbors Stage two Gravitational forces between planetesimals caused them to collide and merge, forming larger and larger objects. Because larger objects have stronger gravitational pulls, eventually almost all of the planetesimal material was swept up into a few large "protoplanets" (accumulations of matter that would eventually evolve into the planets we know today). The asteroids and comets originated as collisions between planetesimals and protoplanets sent out small chunks of material that escaped capture After 100 million years, we have Nine protoplanets. Dozens of protomoons. A glowing protosun at the center. Roughly a billion years were required to "sweep" the system clear of interplanetary "trash." This is a period of intense meteoritic bombardment whose effects on the moon and elsewhere are still evident today

There are two conflicting views on how the Jovian planets formed. View one 4 largest protoplanets became massive enough to enter a 3rd stage of evolution - sweeping up large amounts of gas directly from the solar nebula. View two Giant planets formed through instabilities in the cool outer regions of the solar nebula - mimicking on small scales the collapse of the initial interstellar cloud. Many of the Jovian moons probably also formed by accretion. Some of the smaller moons may be captured planetesimals. Eventually, the sun blew away any remaining gas between the planets, which is why we don't see it today (the outer planets must have formed before the nebular gas dispersed

The closer to the protosun, the hotter the temperature. The temperature determines what could form where and when. (Note that as the solar nebula contracted due to gravity, it heated up as it flattened into a disk.) In the innermost regions (Mercury), only metallic grains could form due to the high temperature. At 1 AU, rocky, silicate grains could form. Beyond 3 or 4 AU, water ice could exist, and so on. More and more matter could condense out at greater and greater distances from the sun. Further out, water vapor, ammonia, and methane could condense into solid form, creating the cores of the Jovian planets.

Planetesimals beyond the orbit of Mars failed to accumulate into a protoplanet due to the large gravitational field of Jupiter constantly disturbing their motion. These are in the asteroid belt and also include the Trojan asteroids. Planetesimals further out were "kicked" into outer orbits and form the Oort cloud. Most planetesimals formed beyond Neptune are still there and make up the Kuiper belt. The condensation theory could not account for the water and other volatile gases found on Earth and elsewhere. Comets, containing both water and other volatile gases, bombarded the inner planets after they were formed. Thus, the water on Earth originated in comets

Random collision of planetesimals and other bodies are allowed within the current condensation theory. These random collisions can be used to explain everything from Venus' slow retrograde motion (due to two protoplanets of comparable mass colliding nearly head-on) to the formation of Earth's moon.

More than 170 extrasolar planets have been found in more than 145 separate systems. We generally can't observe any of the extrasolar planets directly. As a planet orbits a star, gravitationally pulling one way and then the other, the star "wobbles" slightly - we can measure this wobble and determine the mass of the planet

5 % of nearby stars surveyed so far show signs of extrasolar planets. About a dozen of these systems contain more than one "observed" planet. These planets are usually Jupiter-sized and nearby their parent stars - called "hot Jupiters." These planets often appear to be the sole large body in their system. The above two facts are due to a selection effect - the effects of smaller planets and those located at larger distances from their parent stars are difficult to detect

Planetary systems are quite common. Those systems discovered so far do not look like our own. We have explanations for how Jupiter-like planets can wind up close to the parent star (compared to our system), but we don't yet know if that is the norm (or whether it's more common for Jupiter-like planets to be farther out as in our solar system

The Sun is the Largest Object in the Solar System The Sun contains more than 99.85% of the total mass of the solar system If you put all the planets in the solar system, they would not fill up the volume of the Sun 110 Earths or 10 Jupiters fit across the diameter of the Sun he Sun goes through periods of relative activity and inactivity The Sun's interior has three layers: (1) core (2) radiative zone (3) convective zone Energy generated in the core of the Sun propagates outward through these different layers, and finally, through the atmosphere of the Sun. This process takes tens of thousands of years or more.

Photosphere - the layer we see, 5800 K Chromosphere - the red layer observed using a hydrogen filter, 10,000 K Corona - the incredibly thin outer atmosphere, 1,000,000 K The photosphere is the visible layer of the Sun Sunspots are the most well known feature in the photosphere. Monitoring sunspots reveals the Sun's rotation. The movement of sunspots reveals that the Sun's rotation takes about ...4 weeks The annual change in numbers of sunspots reveals that the Sun experiences an 11-year Sun Spot cycle Magnetic field lines connect sunspots on the Sun's photosphere

plages filaments These features are found in the chromosphere. Above the photosphere, the chromosphere is characterized by its red color - from Ha emission. prominences solar flares Solar magnetic fields also create other atmospheric phenomena coronal mass ejections (CMEs) The most powerful solar flare in 14 years, .. erupted from sunspot 486 in late October of 2003. The explosion hurled a coronal mass ejection almost directly toward Earth, which triggered bright auroras when it arrived on Earth.

The Sun also ejects a stream of charged particles into space known as the solar wind

The Earth's magnetic field produces a magnetosphere that deflects and traps particles from the solar wind protecting Earth

Protects against Solar Flares - violent explosions on the Sun releasing large bursts of charged particles into the solar system Protects against Solar Wind - dangerous stream of charged particles constantly coming from the Sun Northern Lights (Aurora Borealis)

As the charged particles from the Sun interact with the magnetic field around Earth, the particles collide with the nitrogen and oxygen atoms in the atmosphere and excite those atoms to emit light

The Nature of Stars red A star's color reveals its surface temperature F10-01 F10-01 F10-01 What color is this star? blue green photo-spectra Spectra of Stars Diversity Leads to Revolution Annie Jump Cannon Antonia Maury Meghnad Saha Cecilia Payne-Gaposchkin cannon maury saha cecilia Women Computers (1890) computers Annie Jump Cannon (1863-1941) cannon Classification Scheme A B C D E . . . S Antonia Maury (1866-1952) Spectral classes might make more sense if arranged by temperature maury steinr_spectra O B A F G K M A Revolution Most astronomers believed that the differences in spectral lines were due to subtle differences in chemical abundance. Indian physicist Meghnad Saha offered another explanation, which was confirmed at Harvard by Cannon and Maury's work. Meghnad Saha (1893-1956) Theory of thermal ionization of atoms saha Cecelia Payne-Gaposchkin (1900-1979) First PhD in Astronomy from Harvard/Radcliffe cecilia Together Saha and Payne-Gaposchkin Gave theoretical explanation for Cannon's classification scheme. Showed that the differences in spectra (absorption lines) are due to temperature and thermal ionization of atoms not abundance of elements Provided a convincing argument that stars are mostly made of hydrogen. F10-02 Stars are classified by their spectra as O, B, A, F, G, K, and M spectral types What does this give us? a new way to classify stars color, peak wavelength of the black body curve, and spectral class all of which are indicators of a star's temperature Summary of Spectral Classes Stars are classified by their spectra as O, B, A, F, G, K, and M spectral types O B A F G K M hottest to coolest bluish to reddish An important sequence to remember: Oh Be a Fine Guy (or Girl), Kiss Me Overseas Broadcast - A Flash: Godzilla Kills Mothra Over-Budget Adult Films Give Knights Merriment One Boring Afternoon, Frank Grew Killer Marijuana For thousands of nearby stars we can find: the total luminosity the temperature (color or spectral type) the size (radius) the distance CAN WE FIND ANY RHYME, REASON, OR RELATIONSHIPS? Looking for correlations: Height vs. IQ ? Height vs. Weight ? QUESTIONS: Are more luminous stars always larger? What combinations of temperature and luminosity are possible? THE H-R DIAGRAM done independently by Enjar Hertzsprung and Henry Norris Russell graph of luminosity (or absolute magnitude) versus temperature (or spectral class) The Hertzsprung-Russell (H-R) diagram identifies a definite relationship between temperature and absolute magnitude F10-04 HR DIAGRAM absolute magnitude vs temperature or luminosity vs spectral type The Hertzsprung-Russell (H-R) diagram identifies a definite relationship between temperature and absolute magnitude HR DIAGRAM absolute magnitude vs temperature or luminosity vs spectral type MAIN SEQUENCE Goes from top left (hot and bright) to bottom right (cool and dim). 90% of the stars are in the Main Sequence stage of their lives Includes our Sun. Main Sequence stars are found in a band from the upper left to the lower right RED GIANTS Really Big, Not Very Hot but VERY BRIGHT! Betelgeuse: 3500 K , 100,000 times more luminous than the sun radius must be 1000x that of Sun! Btlgeuse Red Giant and Supergiant stars are found above and to the right of the Main Sequence stars WHITE DWARFS Very Small, Very Hot but Not Very Bright Sirius B: 27,000 K, but gives off 1000 times less light than the Sun 100 times smaller than the Sun white_dwarf Tiny White Dwarf stars are found in the lower left corner of the HR diagram Determining the Sizes of Stars from an HR Diagram The Smallest stars are the tiny White Dwarf stars and are found in the lower left corner of the HR diagram Main sequence stars span a range of sizes from the small found in the lower right to the large found in the upper left The largest stars are the Giant and Supergiant stars which are found in the upper right corner Tutorial: H-R Diagram (p. 117) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. 0/0 How does the size of a star near the top left of the H-R diagram compare with a star of the same luminosity near the top right of the H-R diagram? They are the same size. The star near the top left is larger. The star near the top right is larger. There is insufficient information to determine this. 0/0 The star Rigel is about 100,000 times brighter than the Sun and belongs to spectral type B8. The star Sirius B is about 3000 times dimmer than the Sun and also belongs to spectral type B8. Which star has the greatest surface temperature? Rigel Sirius B They have the same temperature. There is insufficient information to determine this. Which is hotter a B3 or an A7? Which is hotter a B0 or a B9? What about the Masses of Stars on the H-R Diagram? Main Sequence stars range from 0.1M to ~100M The masses of Main Sequence stars increase with increasing luminosity, size and temperature Main Sequence stars increase in mass from the lower right to the upper left of the H-R Diagram There is a relationship between mass and luminosity for Main Sequence stars Bigger (more massive) is brighter and hotter! There is a relationship between mass and luminosity for Main Sequence stars the numbers shown are masses in terms of the Sun's mass Bigger (more massive) is brighter and hotter! F10-09B There is no simple relationship for the Mass of Non-Main Sequence stars: Giants and Supergiants: range from M to about 20M White Dwarfs: approximately M or less Average Densities: SUN: about density of water GIANTS: One thousand times less dense than AIR! DWARFS: about 1 million times the Sun's density one teaspoon: 5 tons!!!

The Nature of Stars red A star's color reveals its surface temperature F10-01 F10-01 F10-01 What color is this star? blue green photo-spectra Spectra of Stars Diversity Leads to Revolution Annie Jump Cannon Antonia Maury Meghnad Saha Cecilia Payne-Gaposchkin cannon maury saha cecilia Women Computers (1890) computers Annie Jump Cannon (1863-1941) cannon Classification Scheme A B C D E . . . S Antonia Maury (1866-1952) Spectral classes might make more sense if arranged by temperature maury steinr_spectra O B A F G K M A Revolution Most astronomers believed that the differences in spectral lines were due to subtle differences in chemical abundance. Indian physicist Meghnad Saha offered another explanation, which was confirmed at Harvard by Cannon and Maury's work. Meghnad Saha (1893-1956) Theory of thermal ionization of atoms saha Cecelia Payne-Gaposchkin (1900-1979) First PhD in Astronomy from Harvard/Radcliffe cecilia Together Saha and Payne-Gaposchkin Gave theoretical explanation for Cannon's classification scheme. Showed that the differences in spectra (absorption lines) are due to temperature and thermal ionization of atoms not abundance of elements Provided a convincing argument that stars are mostly made of hydrogen. F10-02 Stars are classified by their spectra as O, B, A, F, G, K, and M spectral types What does this give us? a new way to classify stars color, peak wavelength of the black body curve, and spectral class all of which are indicators of a star's temperature Summary of Spectral Classes Stars are classified by their spectra as O, B, A, F, G, K, and M spectral types O B A F G K M hottest to coolest bluish to reddish An important sequence to remember: Oh Be a Fine Guy (or Girl), Kiss Me Overseas Broadcast - A Flash: Godzilla Kills Mothra Over-Budget Adult Films Give Knights Merriment One Boring Afternoon, Frank Grew Killer Marijuana For thousands of nearby stars we can find: the total luminosity the temperature (color or spectral type) the size (radius) the distance CAN WE FIND ANY RHYME, REASON, OR RELATIONSHIPS? Looking for correlations: Height vs. IQ ? Height vs. Weight ? QUESTIONS: Are more luminous stars always larger? What combinations of temperature and luminosity are possible? THE H-R DIAGRAM done independently by Enjar Hertzsprung and Henry Norris Russell graph of luminosity (or absolute magnitude) versus temperature (or spectral class) The Hertzsprung-Russell (H-R) diagram identifies a definite relationship between temperature and absolute magnitude F10-04 HR DIAGRAM absolute magnitude vs temperature or luminosity vs spectral type The Hertzsprung-Russell (H-R) diagram identifies a definite relationship between temperature and absolute magnitude HR DIAGRAM absolute magnitude vs temperature or luminosity vs spectral type MAIN SEQUENCE Goes from top left (hot and bright) to bottom right (cool and dim). 90% of the stars are in the Main Sequence stage of their lives Includes our Sun. Main Sequence stars are found in a band from the upper left to the lower right RED GIANTS Really Big, Not Very Hot but VERY BRIGHT! Betelgeuse: 3500 K , 100,000 times more luminous than the sun radius must be 1000x that of Sun! Btlgeuse Red Giant and Supergiant stars are found above and to the right of the Main Sequence stars WHITE DWARFS Very Small, Very Hot but Not Very Bright Sirius B: 27,000 K, but gives off 1000 times less light than the Sun 100 times smaller than the Sun white_dwarf Tiny White Dwarf stars are found in the lower left corner of the HR diagram Determining the Sizes of Stars from an HR Diagram The Smallest stars are the tiny White Dwarf stars and are found in the lower left corner of the HR diagram Main sequence stars span a range of sizes from the small found in the lower right to the large found in the upper left The largest stars are the Giant and Supergiant stars which are found in the upper right corner Tutorial: H-R Diagram (p. 117) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. 0/0 How does the size of a star near the top left of the H-R diagram compare with a star of the same luminosity near the top right of the H-R diagram? They are the same size. The star near the top left is larger. The star near the top right is larger. There is insufficient information to determine this. 0/0 The star Rigel is about 100,000 times brighter than the Sun and belongs to spectral type B8. The star Sirius B is about 3000 times dimmer than the Sun and also belongs to spectral type B8. Which star has the greatest surface temperature? Rigel Sirius B They have the same temperature. There is insufficient information to determine this. Which is hotter a B3 or an A7? Which is hotter a B0 or a B9? What about the Masses of Stars on the H-R Diagram? Main Sequence stars range from 0.1M to ~100M The masses of Main Sequence stars increase with increasing luminosity, size and temperature Main Sequence stars increase in mass from the lower right to the upper left of the H-R Diagram There is a relationship between mass and luminosity for Main Sequence stars Bigger (more massive) is brighter and hotter! There is a relationship between mass and luminosity for Main Sequence stars the numbers shown are masses in terms of the Sun's mass Bigger (more massive) is brighter and hotter! F10-09B There is no simple relationship for the Mass of Non-Main Sequence stars: Giants and Supergiants: range from M to about 20M White Dwarfs: approximately M or less Average Densities: SUN: about density of water GIANTS: One thousand times less dense than AIR! DWARFS: about 1 million times the Sun's density one teaspoon: 5 tons!!!

nterstellar medium Gas = Hydrogen Dust = Carbon and Silicon Eagle Nebula Stars condense from clouds of gas and dust (the interstellar medium) that exist throughout the disk of the galaxy Becoming a Star Step 1 - Cloud collapses Why do these clouds of gas and dust collapse? One idea is that a shockwave from the explosion at the death of a star known as a supernova cause the gas and dust cloud to become unstable and start to collapse SN1987A shockwave CygnusLoop_hst Becoming a Star Step 1 - Cloud collapses As the cloud collapses, the center becomes very very hot and very very dense - Begining of Star Birth As the gas cloud collapses due to gravitational forces, the core becomes hotter and the density inside the core increases Eventually, the temperature and density reach a point where nuclear fusion can occur Becoming a Star Step 2 - Fusion Fusion is the combining together of light atoms, into heavier atoms TB09-01 For all Main Sequence stars, the temperature and density in their cores are so great that Hydrogen atoms combine to make Helium atoms and release energy - a process known as thermonuclear fusion 4H He + energy Becoming a Star Step 3 - Balance All Main Sequence stars are in hydrostatic equilibrium Fusion produces radiation (light) that creates an outward pressure During hydrostatic equilibrium there is a balance between the gravitational collapse of the star pushing inward and the outward pressure produced by photons from nuclear fusion in the core. It takes a few million years to get there but - stars spend most of their life time as a Main Sequence star Bigining to MS Stars spend most of their life time as a Main Sequence star 90% of the whole life of all stars is spent on the Main Sequence 90% of all stars are found on the Main Sequence Stars often form in pairs called "Binary Stars" These stars can orbit each other much like a star and a planet, and in some cases the stars pass in front of each other - we call these "Eclipsing Binary" stars binary-star_sml eclipsing binary STELLAR LIFETIMES Which will have a greater core temperature and density - a high mass star or a low mass star? Which will then have a greater fusion rate? Which will use up its fuel more quickly? What is the fuel? STELLAR LIFETIMES Consider a main sequence star with 10 times the mass of the Sun It will have higher temps and pressures at the core have greater fusion rates - consumes fuel at 1000 times the rate of the sun be 1000 times as bright and last 1/100 as long "Burn bright, die young." LIFETIMES Bright O-type stars live very short lives (about 10 million years) Very small stars live a long time (100 billions of years) Our SUN: will live a total of about 10 billion years (half used up) The more massive a star, the faster it goes through its main sequence phase T11-01 Tutorial: Star Formation and Lifetimes (p. 119) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. How does the Sun produce the energy that heats our planet? The gases inside the Sun are burning and producing large amounts of energy. Hydrogen is combined into helium, giving off large amounts of energy. Gas inside the Sun heats up when compressed, giving off large amounts of energy. Heat trapped by magnetic fields in the Sun is released as energy. The core of the sun has radioactive atoms that give off energy as they decay. Consider the information given below about the lifetime of three main sequence stars A, B, and C. - Star A will be a main sequence star for 45,000 million years. - Star B will be a main sequence star for 70 million years. - Star C will be a main sequence star for 2 million years. Which of the following is a true statement about these stars? Star A has a mass of 5 solar masses and Star B has a mass of 10 solar masses. How will the fusion rate of Star A compare to the fusion rate of Star B? Star A's fusion rate will be more than two times slower than that of Star B. Star A's fusion rate will be two times slower than that of Star B. Star A's fusion rate will be the same as that of Star B. Star A's fusion rate will be two times faster than that of Star B. Star A's fusion rate will be more than two times faster than that of Star B. Stars spend most of their life cycles on the Main Sequence Main Sequence stars are in hydrostatic equilibrium because nuclear fusion is turning hydrogen into helium and producing enough outward pressure to balance gravitational collapse. 90% of all stars are found on the Main Sequence 90% of the whole life of all stars is spent on the Main Sequence BUT - What happens when the hydrogen runs out?

Stars Leave the Main Sequence The hydrogen atoms in the core of the star that fuse together to create helium, start to run out and fusion begins to slow down The system becomes out of balance Something has to happen to keep the star from collapsing in on itself Out of balance Start running out of hydrogen in the core, now the outward pressure is less than the gravitational collapse Out of balance What will happen to the core? When core hydrogen fusion ceases, a main-sequence star becomes a giant When hydrogen fusion ceases in the core, the star will collapse inward - this causes the layer just outside the core to become so hot and dense that hydrogen fusion will begin in this outer layer. The energy produced by hydrogen fusion in this layer just outside the core causes the rest of the star to expand into a giant star. Helium fusion begins at the core of a giant While the exterior layers expand, the helium core continues to contract and eventually becomes hot enough (100 million Kelvin) for helium to begin to fuse into carbon and oxygen core helium fusion 3 He C + energy and C + He O + energy Main Sequence Stars become Red Giants F11-16 Where do they go after being main sequence stars? Red Giants F11-17 As stars evolve, stars move from being main sequence stars to Red Giants where they increase in luminosity and brightness and decrease in temperature postmainsequence Variable Stars Change brightness because their diameter is fluctuating (big/bright to small/dim and back again) RR Lyrae variables (periods less than 24 hours) Cepheid variables (periods between 1 & 100 days) Mira variables (periods greater than 100 days) InterstellarCloud (gas and dust) Main Sequence Star Red Giant The Life of a Star What happens after core helium fusion stops? The shell and core equilibrium game continues! Depending on the mass of the star, heavier elements are produced: carbon, oxygen, neon, silicon, the heaviest element being iron. We are all made of Star Stuff!! So what happens after the giant phase? It depends on the mass of the star! Low Mass stars ( 8 M ) The core runs out of fuel! Shell fusion begins outside the core. Low Mass stars (< 8 M ) Example of a low-mass giant: its outer layers and core F12-02 The core runs out of fuel! Shell fusion begins outside the core. Eventually the process of shell fusion creates too much outward pressure and energy which explosively pushes out the outer layers of the star and produces a planetary nebula. Low Mass stars (< 8 M ) Main Sequence Star Red Giant PlanetaryNebula Low mass stars (< 8 M ) InterstellarCloud (gas and dust) F12-04A Ring Nebula The burned-out core of a low-mass star becomes a white dwarf Surrounding planetary nebula disperses leaving behind just the remaining WHITE DWARF White Dwarf A core with remaining mass less than 1.4 M. These tiny star remnants are approximately the size of planet Earth One cubic centimeter (like a sugar cube) of a White Dwarf star would weigh several tons. F12-04A Ring Nebula White Dwarf Main Sequence Star Red Giant PlanetaryNebula White Dwarf Low mass stars (< 8 M ) InterstellarCloud (gas and dust) What happens to white dwarfs? Do they just sit there?? If the white dwarfs are isolated, yes. They will cool down and become BLACK DWARFS. F12-06 Sirius and its White Dwarf companion binary BUT: White dwarfs are not always left alone. Sometimes they can have a companion star! As its companion evolves and gets bigger, the white dwarf can steal mass from it. The stolen matter forms an external layer which can quickly ignite and shine brightly creating a Nova. What's a Nova? A nova occurs in binary systems where a white dwarf is pulling mass from its companion. A nova is a relatively gentle explosion of hydrogen gas on the surface of a white dwarf in a binary star system. This process does not damage the white dwarf and it can repeat. binary binary Sometimes the mass transfer can be excessive. So excessive that the white dwarf will not be able to support the mass it gains. So, what would have been a nova becomes a SUPERNova! Main Sequence Star Red Giant Planetary Nebula White Dwarf Pulling material off of a companion star Nova Supernova Ia Leaves no remnant! White Dwarf Low mass stars ( 8 M ) Have a Different Story Fusion in the core continues through many more stages than for low mass stars Heavier elements are produced: carbon, oxygen, neon, silicon, and so on up to iron We're all made of star stuff!! A series of different types of fusion reactions occur in high-mass stars massive_star_fusion_layers Core runs out of fuel! Gravity ( ) wants to collapse the star! High-Mass Stars (> 8 M ) The core and outer layers run out of fuel. The star then collapses, due to gravity. The mass, however, is high enough that nothing can balance the gravitational collapse and..... Supernovae -Type II The collapsing outer layers of the star will collapse against and bounce outward off the compact collapsed core in an explosive event sending out a shockwave. This explosive event is called a Type II Supernova!!! During the Supernova, heavier elements are crated from fusion events, like magnesium, lead, or gold. A Supernova Type II occurred here before we did. The atoms that created our world and solar system come from nuclear fusion in stars and from Supernovae events! We are all made of star stuff! Gravity ( ) wants to collapse the star No outward pressure = implosion Rebound of outer layers against the core = supernova High-Mass Stars (> 8 M ) 1987a 1987a After Before Supernovae can be as bright as a whole galaxy! Big Main Sequence Star Red Giant Type II Supernova High-Mass Stars (> 8 M ) InterstellarCloud (gas and dust) What happens to the core after a supernova? the whole story depends on mass! neutron star the really big ones: remaining mass of 1.4 M to about 3 M black hole the really really big ones: remaining mass greater than 3 M Neutron Stars A core with remaining mass of 1.4 to 3 M, composed of tightly packed neutrons. These tiny stars are much smaller than planet Earth -- in fact, they are about the diameter of a large city (~20 km). One cubic centimeter (like a sugar cube) of a neutron star, would have a mass of about 1011 kg! (hundreds of billions of pounds!) F12-24 Neutron Star Supernova_Neutron star Neutron Star Supernova Pulsars - The discovery of rotating neutron stars First detected in 1967 by Cambridge University graduate student Jocelyn Bell. She found a radio source with a regular on-off-on cycle of exactly 1.3373011 seconds. Some scientists speculated that this was evidence of an alien civilization's communication system and dubbed the source LGM (Little Green Men!!!) Today, we know pulsars are rapidly spinning neutron stars. Lighthouse Model Lighthouse_pulsar PulsarDiagram Black Holes A remaining core with a mass of more than 3 M, will continue to collapse into an infinitely small location in space. We cannot observe what is left behind, directly. We can only detect its presence if it has a companion star, and it attracts material in an accretion disk. Black Holes A black hole is a collapsed stellar core. It is a location in space of enormous gravitational attraction. The gravitational attraction is so strong that photons of light cannot even escape (that's why it's black)! x1 To detect a black hole, we look for the x-rays given off by material as it falls toward the black hole. Big Main Sequence Star Red Giant Type II Supernova Neutron Star High-Mass Stars (> 8 M ) Black Hole InterstellarCloud (gas and dust) Tutorial: Stellar Evolution (p. 133) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. 0/0 Black holes are formed by a lack of any light in a region of space. supernovae from the most massive stars. supernovae from binary stars. collapsed dark nebulae. 0/0 Which of the following lists, in the correct order, a possible evolutionary path for a star? Red Giant, Neutron Star, White Dwarf, nothing Red Giant, Type I Supernova, Black Hole Red Giant, Type II Supernova, Planetary Nebula, Neutron Star Red Giant, Planetary Nebula, White Dwarf Red Giant, Planetary Nebula, Black Hole

Galaxy - a "gargantuan" collection of stellar and interstellar matter (stars, gas, dust, neutron stars, black holes) isolated in space and held together by its own gravity. Milky Way - the galaxy we're part of, also referred to as the Galaxy. We can't see all of our galaxy (just like you can't see all of Earth without leaving the planet), so much of what we know is based on comparisons with similar objects. Our Milky Way Galaxy Above average size Spiral Galaxy Contains billions of stars Galaxy Components: Bulge Disk Halo bt2lf1801A_a Our Milky Way Galaxy Bulge - a thick distribution of warm gas and stars around the galactic center. Disk - an immense, circular, flattened region which contains most of the galaxy's luminous stars and interstellar matter. Halo - a spherical distribution of old stars surrounding the galaxy. galaxynosun Parts Summary Table14-01 Which is our view of the Milky Way? A is what we see from Earth inside the Milky Way while B is what the Milky Way "might" look like if we were far away looking back at our own galaxy from some other galaxy. Where in the disk are we? bt2lf1801A_a Where in the disk are we? F14-00 F15-01C To answer our question, we want to imagine being able to look at the Galaxy from above or below, where dust is not a problem! If we look at the Galaxy from an edge-on view across the disk, dust is in the way of seeing across the galaxy. Where in the disk are we (or how far from the center are we) ? Globular clusters (1000s of stars that were all born from the same cloud at the same time) are distributed uniformly around the Milky Way. The center of this distribution is located at the galactic center. globularcluster Globular Cluster M13 In 1917, Harlow Shapley plotted the distribution of globular clusters in the Milky Way in an effort to learn our location within the Galaxy. The center (maximum) of the distribution of globular clusters shows us where the center of the galaxy is. shapley Where in the disk are we (or how far from the center are we) ? We know we are not in the center of our solar system AND We know we are not in the center of our galaxy (We are also NOT in the center of the universe) We are located in the disk about 25,000 ly out from the center galaxysun Where in the disk are we (or how far from the center are we) ? Tutorial: Milky Way Scales (p. 135) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask me or another group. Imagine that you could travel at the speed of light. Starting from Earth, how long would it take you to travel to the center of the Milky Way Galaxy? It would happen in an instant. 25 years 250 years 2,500 years 25,000 years Answer the following question using the image below, which represents the Milky Way Galaxy. Approximately how large is the diameter of the white dot? 1. 1,000 light years 2. 10,000 light years 3. 50,000 light years 4. 100,000 light years 5. 500,000 light years Non-visible light allows us to observe the center of the galaxy Multiwavelength MW The galactic center is an active, crowded space The center of the Milky Way is located near the constellation of Sagittarius. F14-08 What do the disks of other spiral galaxies look like? M83 observed in both visible light and radio wavelengths. Although the visible light from stars is blocked by dust we can still observe the disk of our galaxy by looking at Doppler shifted radio wavelength light emitted from hydrogen gas. F14-07 The Milky Way galaxy using Doppler shift and radio wavelengths F14-06 As we look along the disk of the Milky Way (from Earth), we see light from hydrogen atoms Doppler shifted by different amounts - this Doppler shift is used to determine how fast the stars and gas of the disk are moving (rotating). F14-11 The Milky Way Galaxy's Rotation Curve Problem: Why do all the stars in the Milky Way galaxy, beyond or outside of the central bulge appear to be moving at about the same speed? Solid Body Rotation Curve Example: Merry-Go-Rounds Every part of the merry-go-round "orbits" the center in the same amount of time Inner part moves slow Outer part moves fast Solid body rotation merry-go-rounds bt2lf1819A_a Kepler's Law Rotation Curve Example: Our Solar System The period of each planet depends on its distance from the Sun Kepler's 3rd Law: P2 = a3 Planets farther away form the sun go much slower Almost all the mass is in the center; the Sun bt2lf1819B_a bt2lf0801a_a What does observing the light from stars in other galaxies tell us? The visible light from stars we observe suggests that the majority of the mass of the Milky Way should be concentrated near the center. Looks bright at center so most the mass should be at the center. Distance from the Galactic Center Light from stars F14-08 Distance from the Galactic Center Mass However the flat rotation curve tells a different story? Because there is a flat rotation curve there should be an equal amount of mass distributed everywhere throughout the galaxy's disk and halo. F14-11 Distance from the Galactic Center Mass So which mass curve is right? The mass curve determined from the rotation curve is our current best model for how the mass of the galaxy is distributed. Mass evenly distributed everywhere in the disk and halo. But that is a problem. Where is all the missing mass and why can't we see it? F14-11 sideview sideview Where is the missing Mass? Dark matter - massive objects (matter) that are (is) distributed evenly around the galaxy in both the halo and disk. Dark Matter All galaxies exhibit the same problem of "missing" matter Dark Matter Does not emit light Not mysterious or evil matter, just not seen Possibilities: Brown Dwarfs, Neutrinos, Black holes, MACHOS, WIMPS vera_rubin We cannot see 90% of the matter that makes up our Galaxy!! Vera Rubin Discoverer of Dark Matter

Hubble's Galaxy Classification American astronomer Edwin Hubble was the first to categorize galaxies in a comprehensive way. His observations were performed on the 2.5 m optical telescope on Mount Wilson in California in 1924. Basic Hubble classification scheme: spirals, barred spirals, ellipticals, and irregulars. Spirals Contain a flattened disk where spiral arms are found, a central galactic bulge with a dense nucleus, and an extended halo of faint old stars. Denoted by the letter S and classified as type a, b, or c according to the size of the central bulge (Sa have the largest bulge, while Sc have the smallest). Sa have the tightest spiral patterns, with Sc having the loosest spiral patterns and most knots or clumps. Bulges and halos contain large numbers of reddish old stars and globular clusters. However, most of the light comes from the younger stars, which give spirals an overall whitish color. Disks are typically gas and dust rich, with Sc galaxies containing the most. Spiral arms appear blue due to young, massive O and B type stars. F15-01 F15-02 Variety of Spiral Arms Flocculent spirals Grand-design spirals (highly organized) F15-03 Barred-Spirals Contain an elongated "bar" of stellar and interstellar material passing through the center and extending beyond the bulge, into the disk. The spiral arms project from near the ends of the bar rather than from the bulge (as they do in normal spirals). Designated by the letters SB and subdivided into the a, b, and c groups. Other than the presence of the bar, exactly the same as normal spirals. Milky Way's bulge has some central elongation, and probably contains a bar. F15-06 Ellipticals Have no spiral arms and no obvious disk. Other than a dense central nucleus, often exhibit little internal structure. As with spirals, stellar density increases sharply in the central nucleus. Denoted by the letter E. Slightly flattened systems are denoted E0, and the most elongated ellipticals are denoted E7. Note that galaxy shape can be difficult to determine based on visual appearance alone. Large range in size and number of stars of ellipticals. Giant ellipticals range up to a few megaparsecs in diameter. Dwarf ellipticals may be as small as one kiloparsec in diameter. Dwarf ellipticals outnumber their larger counterparts 10 to 1, but make up a smaller percentage of total mass compared to their larger cousins. Dwarf ellipticals are not simply small ellipticals, but represent an entirely different class of galaxy. F15-07 Ellipticals Some giant ellipticals contain disks of gas and dust in which stars are forming. These are likely the results of mergers between gas-rich galaxies. Such mergers alter the appearance of galaxies. In between an E7 elliptical and Sa spiral are a class of galaxies known as S0 galaxies (no bar) and SB0 galaxies (bar present). Also called lenticular galaxies. Contain a stellar disk, but no gas or dust. S0s are likely closely related to ellipticals. Irregulars Any galaxy that's not an elliptical or spiral. Tend to be rich in interstellar gas and young, blue stars. Lack any regular structure. Tend to be smaller than spirals and larger than dwarf ellipticals. Most common irregulars are the dwarf irregulars. Dwarf ellipticals and dwarf irregulars combined make up the vast majority of galaxies and are often found near a larger "parent" galaxy. Two subclasses: Irr I and Irr II. Irr I look like misshapen spirals, such as the Large and Small Magellanic Clouds (satellite galaxies of our Milky Way). Contain ongoing star formation. Irr II galaxies are much more rare, and often have an "explosive" or filamentary appearance. Probably the result of interaction between two more normal systems. F15-12 The Hubble Sequence Hubble regarded the tuning fork as an evolutionary sequence from left to right. We still refer to ellipticals as early-type galaxies, and spirals as late-type galaxies. However, there is no direct evolution from one type to another for an isolated system. Galaxy collisions may however change the structure of a galaxy from one type to another. F15-10 Hubble Tuning Fork Galaxy Classification and Properties: Lecture Tutorial (p. 139) breakout_GalaxyClassification_mosaic1a F15-02 breakout_GalaxyClassification_mosaic1a breakout_GalaxyClassification_mosaic2a 1 2 3 4 5 6 7 8 F15-01 Clusters of Galaxies Local Group - group of galaxies containing the Milky Way and Andromeda among others, a little over 1 Mpc in diameter. Contains 45 known galaxies. Galaxy cluster - a group of galaxies held together by their mutual gravitational attraction. Virgo Cluster - contains more than 2500 galaxies, extending about 3 Mpc across. Figure15-14 Active Galaxies 20 to 25 percent of all galaxies don't fit well into Hubble's classification scheme. Some of these galaxies are among the most energetic objects known. Their luminosities can be thousands of times that of the Milky Way. At visible wavelengths, such objects look like normal galaxies. At other wavelengths, they look drastically different. Galactic Radiation Normal galaxies emit most of their radiation at visible wavelengths (stellar radiation). Active galaxies emit most of their light at wavelengths both shorter and longer than visible (nonstellar radiation). The term active galaxy refers to a system where the abnormal activity is related to violent events occurring in or near the galactic nucleus. Such systems are known as active galactic nuclei. Three types: Seyfert galaxies, radio galaxies, and quasars. Seyfert Galaxies Named for Carl Seyfert, who first observed them in 1943 from Mount Wilson Observatory. Resemble normal spiral galaxies. Most of the energy is emitted from the galactic nucleus. Brightest Seyfert nuclei are 10 times more energetic than the entire Milky Way. 75% of Seyferts emit most of their radiation in the infrared (dust is re-emitting higher energy radiation it has absorbed). Energy emission often varies in time - by as much as 50% in under a year -- the source must be very compact (1 ly across since an object cannot flicker in less time than radiation takes to cross it). Figure15-19 Radio Galaxies Emit large amounts of energy in the radio portion of the electromagnetic spectrum. Centaurus A is one example. The emission does not come from a compact nucleus, but from two huge extended regions called radio lobes (which extend in size comparable to the entire Local Group). Radio lobes jet out from the center - possibly expelled from the nucleus due to a galaxy merger. Despite their name, they actually radiate more energy at short wavelengths. Figure15-21 Common Features of Active Galaxies Compact nucleus Jets Signs of interactions with other galaxies Quasars Brightest known objects in the universe. Known as "quasi-stellar objects" (QSO or quasars for short) due to star-like appearance. Look like stars since they are so far away from us. Radiation is nonstellar and may vary over time. Some show jets and extended emission features. Most emit their energy in the infrared. Believe they are the cores of distant active galaxies (galaxies are too faint to be seen). Figure15-29 Common Properties of Active Galactic Nuclei They have high luminosities. Their energy emission is mostly nonstellar. Their energy output can be highly variable. They often exhibit jets and other signs of explosive activity. Their optical spectra may show broad emission lines, indicating rapid internal motion within the energy-producing region. Energy Production Supermassive black hole - large amounts of energy are produced as matter spirals down onto the central object. Matter emits large amounts of radiation as it is heated to high temperatures due to friction within the accretion disk. Instabilities in the accretion disk can cause varying energy output. Jets are a common feature of accretion flows, although not sure how they are formed (linked to strong magnetic fields). Figure15-30 Energy Emission Emission spans infrared to X rays. Much of the higher energy radiation is absorbed by dust and then emitted in the infrared (reprocessing). Synchrotron radiation - produced as particles spiral around magnetic field lines. Not related to the temperature of the radiating object. Figure15-33 Galaxy Collisions Top left is an image of the Cartwheel galaxy. The ring of young stars was likely created as a smaller galaxy passed through the disk of the larger one. Bottom left is an image of two interacting galaxies, which will eventually merge into one (a billion years from now). No human will ever witness an entire galaxy collision as the process takes many millions of years. Figure16-06 Figure16-07 Galaxy Collisions Computers can simulate a galaxy collision in a matter of hours. Galaxies in clusters collide quite often. In small groups, the galaxies move slowly and tend to stick together and merge. In large groups, the galaxies move more quickly and pass through each other without merging. In a few billion years, Andromeda (our nearest large neighbor) will collide with the Milky Way (it's moving 120 km/s towards us). Figure16-08 Galaxy Collisions While a collision will wreak havoc on the large scale structure of a galaxy, the individual stars remain unaffected. The stars in a galaxy are so small compared to the distances in between them, that the stars in two colliding galaxies generally never come into actual contact. The stars may be pulled / pushed to new locations due to the gravitational interactions, but they do not (in general) run into each other. Galaxy Formation and Evolution We know of no simple evolutionary connections among the various categories in Hubble's classification scheme. The theory of galaxy formation is still very much in its infancy. Complicating the picture are the numerous collisions and mergers a galaxy can experience during its lifetime. Galaxy Interactions Left alone, a galaxy will evolve as predicted by stellar evolution. However, few galaxies remain in isolation their entire lifetimes. Interactions can rearrange a galaxy's stars, as well as trigger a sudden burst of new star formation. See above for examples of starburst galaxies, where the interaction induced star formation is extremely intense. Encounters may also "divert fuel" to a central black hole, powering violent activity in some galactic nuclei. Figure16-11 Galaxy Interactions Computer simulations have shown that dark matter halos surrounding galaxies are crucial to galaxy interactions. Galactic cannibalism - when a less massive galaxy interacts with a more massive galaxy, the more massive galaxy takes matter from the less massive one. Galaxy interactions between similarly (but not exactly the same) sized disk galaxies can produce the appearance of spiral arms. The entire event takes several hundred million years. Figure16-13 Making the Hubble Sequence While collisions are random events, and not a true evolutionary process, they can form one type of galaxy from another. If two comparable disk galaxies collide, the resulting galaxy (after a merger) will be an elliptical. If a large galaxy merges with a smaller one, the large galaxy maintains its original form. Spiral galaxies are more common in less dense regions of the universe - their disks are easily destroyed by collisions and mergers, which are much more common in the centers of galaxy clusters (regions of high density). Black Holes and Active Galaxies Since quasars are much more common at greater distances from us, they must have been more prevalent in the past than they are today. Quasars represent an early stage of galaxy evolution denoted by large activity, after which galaxies calm down. The Quasar Epoch Where did the supermassive black holes which form quasars come from? We're not yet sure. Since quasars "eat" about a thousand solar masses of material per year, they could not maintain their luminosities for very long. Quasars likely run out of fuel after a few million years. So, most quasars were relatively brief events that occurred a long time in the past. To make a quasar, we need a black hole and enough fuel to power it. Fuel (gas and stars) was in abundance in the early universe. But, how do you get a supermassive black hole? One possibility - smaller (more normal sized) black holes merged in galaxy centers. Another likely event - when galaxies collide and merge, so do their central black holes. Earliest known quasars formed 13 billion years ago. The height of the quasar epoch occurred 11 billion years ago. The Quasar Epoch In 2002, Chandra (X-ray observatory) discovered a binary black hole. The two massive black holes are falling in toward each other, and are predicted to merge in about 400 million years. See top left. This is the first direct evidence that such events do actually happen. Since distant galaxies are much fainter than their quasar centers, it's difficult to discern any galactic structure in quasar images. See top right for Hubble images of a quasar and its parent galaxy (first time a host galaxy was actually seen). Active galaxies tend to be in clusters. Quasar activity appears to be intimately linked to interactions and collisions in galaxy clusters. Figure16-14 Figure16-15 Active and Normal Galaxies Rapid decline in number of quasars marks the end of the quasar epoch - roughly 10 billion years ago. Today, the number of quasars has dropped to virtually zero (recall the closest one to us is hundreds of megaparsecs away). The black holes don't vanish - so galaxies should still have central black holes after the quasars have run out of fuel. The black holes become active again when given new sources of fuel - this is what happens for active galaxies. Matter gets near the black hole, and a previously normal galaxy becomes active once again. Active Galaxy Formation The largest black holes tend to be found in the most massive galaxies. The most massive black holes power the brightest active galactic nuclei. These galaxies formed from major mergers of large galaxies, which would result in ellipticals. So radio galaxies should be associated with ellipticals. Smaller mergers would have formed spirals and the less active Seyferts.

Size and scale of the Universe: Reference Points Solar System - Sun, planets, asteroids, comets Galaxy - hundreds of billions of stars, gas and dust Clusters of galaxies - millions of galaxies Universe - everything! solarsystem mw_aat Ulta Deep Field universe What is the Universe? Everything we can know about is part of the universe. Everything we do know about is part of the universe. Everything! solarsystem mw_aat Ulta Deep Field universe Galaxies are redshifted! In 1903 at Lowell Observatory in Flagstaff, Arizona, Vesto Slipher was the first to measure the redshift of a spiral nebula (now known as a galaxy). Slipher realized that the redshift of the spectrum of the spiral nebula (galaxy) meant that it was moving away from us at a very high speed. slipher F15-28 Recall: The amount the lines in a spectrum are shifted indicates how fast the galaxy is moving. ALL Galaxies have redshifts - farther from us greater redshifts! Many other scientists made observations similar to Slipher's. In 1929, Edwin Hubble and Milton Humason put their observations together in a way that led to the first realization that the universe changes - in fact, the universe is expanding! hubble humason F15-29 Addison Wesley IF20.18 ALL Galaxies have redshifts - farther from us greater redshifts! F15-29 The units of the slope of the line in the Hubble Plot are Speed/Distance OR (Distance/Time) / Distance OR 1/Time SO the inverse of the slope is a unit of "Time". What time is it? THE AGE OF THE UNIVERSE!!!!!! F17-06 the more distant the object the farther back in time we are seeing it the faster it is moving away from us and the bigger its redshift. Does the Universe Change? Einstein published his theory in two steps: special theory of relativity (1905)...how space & time are interrelated general theory of relativity (1915)...relationship between gravity and space & time EinsteinPictureSpaceTimeII young_einstein einstein4 Albert Einstein (1879 - 1955) "Nature conceals her secrets because she is sublime, not because she is a trickster." Space and Time Hermann Minkowski (1864 - 1909) German physicist Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality. The Universe is four-dimensional A good way to think of the universe is to use Einstein's description of space-time, the four dimensional fabric that makes up our universe. The universe has three spatial dimensions (length, width, height) and one temporal (time) dimension spaceTime_Panet SpaceTimesideView Space-time and Gravity Albert Einstein stunned the scientific world in 1915... with publication of his general theory of relativity it illustrates how space-time can be used to describe the behavior of how mass and light interact - in a way its an explanation of how gravity works Isaac Newton saw gravity as a mysterious "force." even Newton had problems accepting this concept of "action at a distance" -- how the force of gravity is transmitted through space Einstein theorized that the "force" of gravity arises from distortions of spacetime itself! Matter Warps spacetime like weights on a taut rubber sheet. The greater the amount of mass, the greater the warping of spacetime. fS302 Matter Warps Spacetime The Strength of Gravity The greater the amount and concentration of mass (density), the more that spacetime warps, the stronger gravity becomes. The distance away from the center that space-time will be curved is the same for all three objects. White dwarf causes steeper curvature at Sun's former position. Black hole creates infinitely deep hole in the fabric of space-time but still warps out to the same distance. Nothing can escape from within the event horizon of the Black hole. fS316 Black Hole Space Time space time fabric Matter tells space-time how to curve. Curved space-time tells light and matter how to move. Mass and Spacetime Orbits can now be explained in a new way. an object will travel on as straight a path as possible through spacetime fS314 Warping of Space-time and Black Holes Black Holes, Light and Space time. even though it has no mass, light will be affected by warped space-time its path through space will be bent within the event horizon, it cannot climb out of the hole Black Holes, Matter and Space time... the tidal forces are tremendous the object would be "stretched and squeezed and time would slow down" f1711_a f1713 Evidence for Space Time and General Relativity - Gravitational Lensing Light will always travel at a constant velocity. therefore, it will follow the straightest possible path through space-time if spacetime is curved near a massive object, so will the trajectory of light During a Solar eclipse in 1919, two stars near the Sun... were observed to have a smaller angular separation than is usually measured for them at night at other times of the year This observation verified Einstein's theory... fS321 curvature Gravitational Lensing Since that time, more examples of gravitational lensing have been seen. They usually involve light paths from quasars & galaxies being bent by intervening galaxies & clusters. fS322 fS323a fS323b Einstein's Cross an Einstein ring galaxy directly behind a galaxy Spacetime for All The reality of spacetime is the same in all reference frames. we cannot visualize the 4D spacetime since we can't see through time we perceive a 3D projection (view) of spacetime while spacetime is the same for all observers, their 3D perceptions of it (e.g. space & time) can be very different fS307a fS307b By analogy... we can all agree on the shape & size of this book in 3 dimensions But... the following 2D projections (views) of the same book all look very different SO WHAT IS THE POINT!! What is Einstein's theory of what the universe is composed of and how does it explain gravity and how the universe is changing? Remember the Universe, composed of a fabric of space-time, is expanding. 1 - 2 - 3 - 4 Dimensions A point moved in one direction creates a line (1D). A line moved in a direction 90º to itself creates a plane (2D). A plane moved in a direction 90º to itself creates a space (3D). A space moved in a direction 90º to itself creates a 4D space. Unfortunately we can not perceive this 4-D hyperspace...any space > 3D fS306 dimension... an independent direction of possible motion The Rules of Geometry fS313a fS313b fS313c flat (Euclidean) geometry spherical (curved-in) geometry saddle-shaped (curved-out) geometry The geometry you know is valid when drawn on a flat surface. The rules change if the surface is not flat. The Universe and Spacetime Galaxies are moving away from us. Galaxies that are further away are moving faster. The universe is expanding! The expansion of the Universe creates more space and time balloonuniversesmall balloonuniverselarge As the universe expands, is the solar system expanding with it? Yes, if new spacetime is forming, then there is more space between all objects than there used to be. Yes, if new spacetime is forming, then all objects are being pushed apart. No, since the solar system is held together with gravity, the objects within it cannot be moved further apart. What about the galaxies - are they expanding as well? It's the same thing as with the solar system - gravity keeps the galaxies the same size. Yes, there's more spacetime between all of the objects in the universe. So there's more empty space between the objects in a galaxy. The Universe is expanding The redshifts of galaxies is evidence that the universe is expanding. balloonuniversesmall balloonuniverselarge The Universe is expanding If the universe is expanding, it must have been smaller in the past. If it was smaller in the past, then there must have been a beginning for the universe Working backwards, what would the universe be like at the beginning? Hot, dense, tiny balloonuniversesmall The Big Bang marks the time when the Universe began In the 1940s, based on Hubble's Law, George Gamow proposed that the universe began in a colossal explosion In the 1950s, the term BIG BANG was coined by an unconvinced Sir Fred Hoyle The BIG BANG is the event that marks the time when the universe began. The BIG BANG is the event that marks the time when the universe began - the beginning of the expansion. But what did the universe look like at the beginning? All of the universe as we know it now, was once a single point-like location of infinite Temperature and Energy but was NOT composed of any Matter. balloonuniversesmall balloonuniverselarge What happened after the Big Bang? What evidence is there to support the idea of a Big Bang? ~380,000 years after the event of the Big Bang, the Universe cooled to a temperature of 3,000 K, and light, which could not propagate until then, began to spread in all directions. Working backwards, we should be able to see some evidence of this signature of light (blackbody radiation) at the time of the early universe. The light released then, almost 14 billion years ago, can still be observed now. The 3,000 Kelvin temperature of the early Universe has dropped to a temperature today of 2.735 K (Blackbody peak in the microwave) - This is known as the Cosmic Microwave Background Radiation!!! The cosmic microwave background radiation that fills all space is evidence for the BIG BANG F17-01 F17-02 F17-00 F17-03 The Blackbody spectrum of the Cosmic Microwave Background Radiation reveals a temperature of 2.735K The microwave background radiation is evidence to support the ideas that: The Universe was once much hotter, denser and smaller. There were times during the early universe when light could not freely travel through space. The Universe began during an event we call the Big Bang. The Universe is approximately 14 billion years old. WMAP_MicrowaveBackground F17-00 COBE WMAP Cosmic Microwave Background Radiation So what does the WMAP ("the best baby picture of the Universe ever taken") tell us? The first generation of stars in the Universe first ignited only 200 million years after the Big Bang, much earlier than many scientists had expected. The new microwave background observations precisely peg the age of the Universe at 13.7 billion years old, with a remarkably small one percent margin of error. The Universe includes 4% atoms (ordinary matter), 23% of an unknown type of dark matter, and 73% of a mysterious dark energy. The new measurements even shed light on the nature of the dark energy, which acts as a sort of an anti-gravity affecting the rate of expansion of the Universe. We might not only be expanding, but the expansion might be accelerating. The Universe - Expansion and the Big Bang The observation that galaxies are moving away from us, tells us that the universe is expanding The observation of the Cosmic Microwave Background Radiation supports the idea that the Universe stated with an event called the The BIG BANG which marks the time when the universe began its expansion from a single point-like location of infinite Temperature and Energy but was NOT composed of any Matter. The Universe is a Blackbody and the Cosmic Microwave Background Radiation tells us that the current average temperature of the Universe is 2.73K. Which corresponds with an age of the universe of approximately 13.7 billion years Olber's Paradox Assume that the universe is infinite in spatial extent and unchanging in time. Then, every line of sight must eventually lead to a star (assuming universe is uniformly populated with galaxies). Stars further away are dimmer but greater in number (the number of stars we see increases as the square of the distance). The brightness of stars decreases as the square of the distance. These two effects should balance, so stars at all distances contribute equally to the total amount of light received on Earth. Implication - no matter where you look in the sky, it should be bright! This idea, combined with fact that the night sky isn't bright, is known as Olber's paradox. So why is the sky dark at night? Either the universe is finite in extent, or it evolves in time, or both. The Birth of the Universe Hubble's law describes the expansion of the universe - all galaxies are rushing away from us according to: Recession velocity = H0 x distance H0 = 70 km/s/Mpc We can determine how long it has taken a galaxy to move away from us using Hubble's law: Time = distance / velocity = distance / (H0 x distance) = 1 / H0. This comes out to an age of 14 billion years. Hubble's law implies that 14 billion years ago, all galaxies lay on top of each other. The Birth of the Universe Almost unanimous view among astronomers: everything in the universe - matter and radiation alike - was confined to a single point at 14 billion years ago. The point exploded, flying apart at high speeds (the Big Bang) marking the beginning of the universe. The present locations and velocities of the galaxies are a direct consequence of that primordial blast. The solution to Olber's paradox - we can only see a finite extent of the universe (even if it's infinite) - that which lies within 14 billion light-years. Anything further would not have had time to reach us. Where did the Big Bang occur? At a single point in the center of the universe. Everywhere in the universe all at once. At a point outside of our universe. We see galaxies moving away from us in all directions. Are we at the center of the universe? Yes, that's the only way most everything else can move away from you. No, we are not at the center of the universe, but the universe does have a center somewhere. No, no matter where you are located at, you would see most other galaxies moving away from you. It's a trick question - the universe has no center. The Universe on the Largest Scales No evidence for structures larger than about 200 Mpc (1 pc is 3 ly, so 200 Mpc is 6,000,000 ly). Universe appears to be homogenous on large scales (the same everywhere) and isotropic (the same in all directions). Cosmological principle - assumptions that the universe is both homogenous and isotropic on large scales. Implications - the universe has no edge (would break homogeneity) and no center (would break isotropy). Distribution of galaxies from the Sloan Digital Sky Survey. The Cosmological Redshift The cosmological redshift is a consequence of the changing size of the universe (not related to velocity at all, unlike the Doppler shift). A photon is attached to the expanding fabric of space, so the photon is lengthened (redshifted). Often think of this as Doppler shift, even though it's not completely correct. The redshift of a photon measures the amount by which the universe has expanded since that photon was emitted. Therefore, redshift can be used to express time. Two Futures The universe can either expand forever, or it can start to contract in the future back into a singularity (the big crunch). The present time is the point at which the two curves above intersect. What determines which future the universe will have? Density! A high density universe contains enough mass to stop the expansion and reverse it. In reality, there may be other factors involved other than just gravity alone. The Shape of the Universe Space is curved (not flat!). The degree of curvature depends on the total density of the universe. This density includes everything (visible matter, dark matter, energy, etc.). The ratio of the universe's actual density to the critical density (the distinction between future expansion or contraction) is called the cosmic density parameter 0. High-density universe (0>1) - universe is closed (space curves so much it bends back in on itself) - think of the surface of a sphere (although this is not quite correct - we need another dimension added to the sphere to be a more accurate picture). A sphere is said to have positive curvature. A low-density universe (0<1) would look akin to a saddle (again, need an extra dimension to make this correct). This is called an open universe. A critical universe (0=1) has no curvature, it is flat. This is the only universe in which Euclidean geometry works on large-scales. The Density of the Universe Most of the matter in the universe is dark (we can only detect it through its gravitational effects on matter we can see). Most believe the amount of dark matter will not raise the density above about 30% the critical value (in other words, most likely, the universe will expand forever). Cosmic Acceleration Using type 1 supernovae, we can measure the expansion. If the universe were decelerating, objects further away should be receding faster than predicted by Hubble's law. In a denser universe, gravity is more effective at slowing the expansion, so the effect would be greater. Supernovae measurements actually indicate that the expansion is accelerating - something other than gravity is acting on the universe. Known as dark energy, this other (yet unknown) force carries energy but has a repulsive effect on the universe, causing empty space to expand. Leading candidate - the cosmological constant. This is an additional vacuum pressure force associated with empty space and effective only on very large scales. This is neither required nor explained by any known laws of physics. It was first introduced by Einstein (who later called it his biggest blunder). Its influence increases as the universe expands. Cosmic Composition Consensus (as of early 2006) is that we are at the critical density. Density is made up of matter (mostly dark) and dark energy. Best estimate - matter accounts for 27% of the total, with dark energy accounting for the remaining 73%. Such a universe will expand forever, and is perfectly flat. The Age of the Universe Globular star clusters - oldest objects in existence, roughly 10 to 12 billion years old. Their ages are not consistent with a critical-density universe without dark energy. This gives an independent verification of currently held cosmology beliefs. Matter and Radiation At the present moment, the density of matter in the universe greatly exceeds the density of radiation. We live in a matter-dominated universe. Early on, the universe was radiation-dominated. According to current theory, the density associated with dark energy remains constant as the universe expands - even though it is important now, it was unimportant in the early universe. The Formation of Nuclei and Atoms According to Big Bang theory, at the very earliest times the cosmos consisted entirely of radiation. During the first minute or so, temperatures were high enough that individual photons of radiation had sufficient energy to transform themselves into matter in the form of elementary particles. This period saw the creation of all the basic building blocks of matter we know today. Everything we see around us formed out of radiation as the early universe expanded and cooled. Helium Formation No matter where you look, stars all have at least around 25% helium by mass. This base level of helium is primordial - created during the early, hot epochs of the universe. The production of elements heavier than hydrogen by nuclear fusion shortly after the Big Bang is called primordial nucleosynthesis. The cosmic elemental abundance was set within 15 minutes after the Big Bang (once the universe cooled and thinned too much, fusion reactions ceased). Nucleosynthesis and the Composition of the Universe Heavy hydrogen, known as deuterium (nucleus contains one proton and one neutron) was produced on the way to making the primordial helium. The left-over amount of deuterium is another indication of the density of the universe. But it only tells us the density of normal matter. Most matter is made up of dark matter, exotic particles whose existence we have yet to conclusively demonstrate in the lab. The Formation of Atoms Period during which nuclei and electrons combined to form atoms is called the epoch of decoupling. Early on, electrons interacted with the radiation. A photon could not travel far without being scattered off by an electron, so the universe was opaque to radiation. During decoupling, the universe became transparent. Decoupling happened when the universe was 400,000 years old. The Horizon and Flatness Problems Horizon problem - Some regions of the universe that have very similar properties are too far apart to have exchanged information within the age of the universe. Flatness problem - There is no natural way to explain why the density of the universe is so close to the critical density. The Epoch of Inflation Grand unified theories - electromagnetism, and the strong and weak forces were all joined into one "superforce." The universe remained in "unified" formation a little too long, and this resulted in the epoch of inflation during which an enormous pressure overcame gravitation. During inflation, the universe doubled in size every 10-34 s or so. The entire episode lasted only 10-32 s, but during this time the universe grew in size by a factor of about 1050. Implications for the Universe Inflation solves the horizon problem - it took places that had already had time to communicate and moved them far apart. Inflation also solves the flatness problem - any curvature that existed before inflation has been spread out so much that the universe now appears effectively flat. The Formation of Large-Scale Structure in the Universe All present large-scale structure in the universe grew from small inhomogeneities (slight deviations from perfectly uniform density). Dark matter clumped first as it interacts least with everything else. Normal matter was drawn to the regions of highest density. Thus, normal matter clumped where dark matter already had. COBE detected slight variations in the background radiation, consistent with the clumping of matter.

Cosmic Evolution Cosmic evolution: Includes seven major evolutionary phases in the history of the universe: particulate, galactic, stellar, planetary, chemical, biological, and cultural evolution. The continuous transformation of matter and energy that has led to the appearance of life and civilization on Earth. What are some characteristics of life? In other words, how do you decide if something is alive? What do we mean by life? Hard to define what we mean by life. Characteristics of living organisms: They can react to their environment and can often heal themselves when damaged. They can grow by taking in nourishment from their surroundings. They can reproduce, passing along some of their own characteristics to their offspring. They have the capacity for genetic change and can therefore evolve from generation to generation to adapt to a changing environment. Life in the Universe The general case in favor of extraterrestrial life is summed up in what are sometimes called the assumptions of mediocrity: Because life on Earth depends on just a few basic molecules. Because the elements that make up these molecules are (to a greater or lesser extent) common to all stars. If the laws of science we know apply to the entire universe (which we assume), then, given sufficient time, life must have originated elsewhere in the cosmos. The opposing view maintains that intelligent life on Earth is the product of a series of extremely fortunate accidents (astronomical, geological, chemical, and biological events unlikely to have happened anywhere else in the universe). Life on Earth Building blocks of life as we know it - amino acids and nucleotide bases (organic, carbon-based, molecules). Amino acids build proteins and nucleotide bases form genes. In 1953, the first scientist proved that you could make amino acids and nucleotide bases from simpler ingredients that would have existed on a young Earth (water, methane, carbon dioxide, and ammonia). Can synthesize biological molecules through nonbiological means. However, these experiments have yet to create a living organism. An Interstellar Origin Suggested that there wasn't enough raw material on Earth for the reactions to occur at a significant rate to form organic material. An alternate possibility - the organic material was produced in interstellar space and arrived on Earth in the form of interplanetary dust and meteors that didn't burn up during their descent through the atmosphere. Large amounts of organic material were detected on comets Halley and Hale-Bopp. How do you decide if something alive is intelligent? Diversity and Culture However it got here, we know life did appear. Anthropologists believe that intelligence is strongly favored by natural selection. Perhaps most important was the development of language. This allowed for cultural evolution (the changes in the ideas and behavior of society). Life as We Know It Generally taken to mean carbon-based life that originated in a liquid-water environment, or life as it is on Earth. In our solar system, Europa and Titan both hold the possibility of harboring life. Most likely planet to harbor life (or to have had it in the past) is Mars. Need to keep in mind that life as we know it can exist in extremely hostile environments (and does on Earth as well). The Drake Equation Statistical equation that gives the probability of intelligent life existing elsewhere in the universe. Several of the factors are a matter of opinion. Important as it divides a huge problem into more workable chunks. We'll go through each of the factors individually. Which of the following factors would you expect to see in the Drake equation? Fraction of stars with planetary systems Fraction of planets on which life arises Average lifetime of a technologically competent civilization All of the above A and B only Rate of Star Formation Milky Way has roughly 100 billion stars now shining and is 10 billion years old. Using the above figures, we have a star formation rate of 10 stars per year. This is probably a fairly good average rate, even though we know it's varied over time. Fraction of Stars Having Planetary Systems If condensation theory is correct, then planetary systems are a natural result of the star formation process. We assign a value near 1 to this factor - we think essentially all stars have planetary systems. We already have proof of other planetary systems, and the number known will just increase as technology improves, so we're not simply being overly optimistic here. Number of Habitable Planets per Planetary System Habitable zone - three-dimensional zone of comfortable temperatures that surrounds every star. Have to exclude the majority of binary star systems. Have to exclude all but 10% of the systems we've found so far as large Jupiter-like planets with interior orbits would destabilize any terrestrial planets' motion. We assign a value of 1/10 to this factor (or 10%). Fraction of Habitable Planets on which Life Arises If the chemical reactions that led to the complex molecules that make up living organisms are completely random, then this factor is probably close to 0. Lab experiments indicate that these reactions aren't completely random (some are more favored than others), so maybe life isn't so rare. We'll be optimistic and go with a value near 1 for this factor. Fraction of Life-Bearing Planets on which Intelligence Arises One school of thought sees natural selection as a universal process and the development of intelligence as inevitable, making this factor nearly 1. The opposing side says that intelligent life has existed on Earth a relatively short period of time compared to simple life, so it's probably rare, making this factor very small. We'll be optimistic and assume the value is nearly 1. Fraction of Planets on which Intelligent Life Develops and Uses Technology If the rise of technology is inevitable, given enough time, then this factor is close to 1. If it is not inevitable, then this factor could be much less than 1. Based on the fact that several tool-using societies arose independently at several places on Earth, we'll go with technology being inevitable and take this factor to be close to 1. Average Lifetime of a Technological Civilization Combining our factors thus far in the Drake equation (10 x 1 x 1/10 x 1 x1 x 1 = 1), we can say that: The number of technologically intelligent civilizations now present in the Milky Way galaxy = lifetime of a technologically competent civilization in years. So if average lifetime is 1000 years, then there are 1000 civilizations present. If the average age is less than a few thousand years, then civilizations are unlikely to have the time to communicate with even their nearest neighbors. Dr. Frank Drake is the Director of the SETI Institute's Center for the Study of Life in the Universe and also serves on the Board of Trustees of the SETI Institute as Chairman Emeritus. In 1960, as a staff member of the National Radio Astronomy Observatory, he conducted the first radio search for extraterrestrial intelligence. He is a member of the National Academy of Sciences where he chaired the Board of Physics and Astronomy of the National Research Council (1989-92). Frank also served as President of the Astronomical Society of the Pacific. He was a Professor of Astronomy at Cornell University (1964-84) and served as the Director of the Arecibo Observatory. He is Emeritus Professor of Astronomy and Astrophysics at the University of California at Santa Cruz where he also served as Dean of Natural Sciences (1984-88). In his spare time Frank enjoys cutting gem stones and growing orchids. Frank has three grown sons and two daughters in college. Both daughters are superb ballet dancers. http://www.seti.org Meeting Our Neighbors Let's assume the average lifetime of a technological civilization is 1 million years. The Drake equation tells us that there are 1 million such civilizations and we estimate their distances to be about 100 light-years apart from one another. Two-way communication would then take 200 years. Could we ever meet them? The speed of the fastest space probes is 50 km/s. It would take us 50,000 years just to reach Alpha Centauri (one of the closest stars). A distance of 100 light-years would take a million years to travel. Radio Searches A cheap way to make contact across interstellar space is to use electromagnetic radiation - fastest means of transferring information from one place to another. Radio is the best bet as its least affected by interstellar dust, etc. Possible to detect "waste" radio emissions as well (like the TV and radio emissions from Earth). The Water Hole Suppose that a civilization has decided to assist searchers by actively broadcasting its presence to the rest of the galaxy. At what frequency should we listen for such an extraterrestrial beacon? The constituents of water (which is thought to be necessary for life), H atoms and OH molecules, radiate near 18 and 20 cm (radio wavelengths). Radio wavelengths interact the least with gas and dust, making the galaxy largely transparent to them. This region of wavelengths is called the "water hole." In the same region of wavelengths, there's the least "static" or noise from other sources (stars and interstellar clouds). Commonly known by the acronym SETI (search for extraterrestrial intelligence), radio searches have been underway since the late 1990s. No signals of extraterrestrial life have been detected. A Telescopes is a tool used to gather light from objects in the universe. There are two different types of telescopes: A refracting telescope uses a glass lens to concentrate incoming light. A reflecting telescope uses mirrors to concentrate incoming starlight. Which of the following is the most important feature of a telescope? Ability to gather light. Ability to see fine detail. Ability to magnify the image. Three main functions of a telescope Most important!! Gather More Light - (bigger Is better) making objects appear brighter followed by to see fine detail (called resolution) and least important, magnify magnification = (objective lens focal length / eyepiece lens focal length) F03-11 A larger objective lens provides a brighter (not bigger) image F03-11 F03-11 F03-11 If you pass white light through a prism, it separates into its component colors. F03-01A ROY G B I V spectrum long wavelengths short wavelengths F03-05 But visible light is only one type of electromagnetic radiation (light) emitted by stars Astronomers are truly interested in the entire spectrum of light! Consider Orion as Seen in Different Wavelengths of light! orion_IR Observations at other wavelengths are revealing previously invisible sights F03-34 UV Ordinary visible Infrared Map of Orion region Sun as seen in visible light from Earth (right) and from space in X-rays by satellites (left) latest_sxt solef F03-30 Radio wavelength observations are possible from Earth's surface F03-31 The Very Large Array (VLA) in New Mexico Differences in the temperature and density of small portions of Earth's atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle. Earth's atmosphere hinders astronomical research F03-24 High above Earth's atmosphere, the Hubble Space Telescope provides stunning details about the universe em_spectrum_observatories Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth's atmosphere. F03-06 Not all EM radiation can penetrate Earth's atmosphere. Tutorial: Telescopes and Earth's Atmosphere pg. 51 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask me or another group. Which is the correct reasoning for why a gamma ray telescope located in Antarctica that is to be used to look for evidence of black holes in the centers of galaxies would not get funded? There is no way to detect the presence of a black hole. Gamma rays are too energetic to detect with a telescope. You can't build a functioning telescope in Antarctica. Gamma rays don't penetrate Earth's atmosphere. Imagine you're the head of a funding agency that can afford to build only one telescope. Which of the three proposed telescopes below would be best to support? A gamma ray telescope in Antarctica. A radio telescope in orbit above the Earth. A visible telescope located high on a mountain in Peru. An ultraviolet telescope located in the Mojave desert. mcdon_fac_struve mcdon_fac_struve_dome het_dome_front mcdon_fac_hjsmith mcdon_fac_hjsmith2_dome McDonald Observatory (Fort Davis, TX) A Few Astronomy Factoids (Or: So You Think You Want to be an Astronomer) Research quality images are monochromatic. Astronomy research is not the safest, but is much safer than it once was due to the use of CCDs over photographic plates. Astronomy research is time consuming and expensive. Astronomers spend more time in front of a computer than at a telescope. Professional astronomers rarely ever actually look through an eyepiece. What is light? In the 17th Century, Isaac Newton argued that light was composed of little particles while Christian Huygens suggested that light travels in the form of waves. In the 19th and 20th centuries Maxwell, Young, Einstein and others were able to show that Light behaves both like a particle and a wave depending on how you observe it. What does light do? Light transfers energy from place to place. Light transfers information from place to place. Everything we know about astronomical objects, we have learned through the analysis of light. Scottish physicist James Clerk Maxwell showed mathematically in the 1860s that light must be a combination of electric and magnetic fields. F03-04 In 1905, Einstein calculated the energy of a particle of light (photon) and proposed the photoelectric effect. Ephoton = hc/l Sphere e- Light horizontal photon But, where does light actually come from? Light comes from the acceleration of charged particles (such as electrons and protons) Waves Wave - (general definition) a pattern that repeats itself cyclically in both time and space Electromagnetic radiation travels through space in the form of waves - a wave is a way in which energy is transferred from place to place without physical movement of material from one location to another. A wave is not a physical object. Wave period - number of seconds needed for the wave to repeat itself at some point in space (time from crest to crest). Wavelength - the number of meters needed for the wave to repeat itself at a given moment in time (length from crest to crest). Amplitude - maximum departure of the wave from the undisturbed state (maximum height). Frequency - number of crests passing any given point per unit time (= 1 / period). Wave Motion Period is given in seconds, frequency is 1/seconds or Hz (Hertz). Wave velocity - a wave moves a distance equal to one wavelength in one period. Velocity = wavelength x frequency Speed of light in a vacuum is constant and is called "c" - it equals 3.0 x 108 m/s. Lecture Tutorial: EM Spectrum (p. 47) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask me or another group. Diffraction and Interference Diffraction - bending of a wave around a barrier (light shining around a corner, etc.). Interference - when two or more waves interact. Interference can be constructive (the waves add) or destructive (the waves subtract, or even cancel each other out completely). So how do we actually get light? F04-12 An atom consists of a small, dense nucleus (containing protons and neutrons) surrounded by electrons - Model Proposed by Niels Bohr 1913 The electron should be thought of as a distribution or cloud of probability around the nucleus that, on average, behaves like a point particle on a fixed circular path. 920424670__atom2 Interactions Between Charged Particles Electrons - negatively charged. Protons - positively charged. Like charges repel, unlike charges attract. Electric field - extends outward from a charged particle. The electric field extends outward in a wave if the particle is moving - we can learn about the particle from afar from studying this wave. Electromagnetic Waves Electromagnetic waves are caused by changing electric and magnetic fields (magnetic fields accompany magnetized objects, just like electric fields accompany charged objects). We learn about distant stars from their electromagnetic waves (radiation). Since the speed of light is finite and constant, when we say an object is 3 LY away (where 1 LY is the distance light travels in a year), we are looking at light that left the star 3 years ago. Photons (light-waves) are emitted from an atom when an electron moves from a higher energy level to a lower energy level. Photons can also be absorbed by an atom when an electron moves from a lower energy level to a higher energy level. F04-05 Each chemical element produces its own unique set of spectral lines when it is excited F04-06 Tutorial: Light and Atoms - p. 65 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask me or another group. If an electron in an atom moves from an orbit with an energy of 5 to an orbit with an energy of 10, a photon of energy 5 is emitted a photon of energy 15 is emitted. a photon of energy 5 is absorbed. a photon of energy 15 is absorbed. None of the above Which of these shows the atom emitting the greatest amount of light? There are three types of spectra. Continuous Spectrum Hot/Dense Energy Source Dark horizontal prism Emission Line Spectrum Dark horizontal prism Hot low density cloud of Gas Absorption Line Spectrum Cooler low density cloud of Gas Hot/Dense Energy Source prism Dark horizontal Tutorial: Types of Spectra - p. 63 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask me or another group. All stars produce dark line absorption spectra. Vega Absorption spectrum graph film So what do we learn from light? The Blackbody Spectrum Intensity - amount of strength of radiation at any point in space. Blackbody - an object that absorbs all radiation falling upon it. Blackbody curve - describes the distribution of re-emitted radiation. Blackbody objects absorb radiation and then re-emit that radiation if it is too remain in a steady state (does not increase or decrease in temperature). Wien's Law - wavelength of peak emission 1 / temperature Stefan's Law - total energy radiated per second temperature4 Temperature We can use blackbody curves as thermometers to determine the temperatures of distant objects (thanks to Wien's law - which relates the wavelength of peak emission to the temperature of the object). Figure02-11 Spectroscopy Spectral lines are indicators of chemical composition. As such, they can be used to identify the chemical composition of any body that emits (or absorbs) light. This is how we know the composition of the sun and other stars. The Doppler Effect (Apparent wavelength / True wavelength) = (True frequency / Apparent frequency) = 1 + (Recession velocity / Wave speed) Objects moving toward us are blueshifted (higher frequency) and objects moving away from us are redshifted (lower frequency). By determining the amount of shift in spectral lines, we can determine an object's recessional velocity (in general how fast it's moving away from us, or sometimes how fast it's moving towards us). The recessional velocity (this applies only to objects moving away from us) relates directly to the object's distance from us, giving us a new way to measure distance. Real Life Examples of Doppler Effect Doppler Radar (for weather) Airplane radar system Submarine radar system Ok, anything with radar Radar gun, used by Law Enforcement Officers... Doppler Effect When something which is giving off light moves towards or away from you, the wavelength of the emitted light is changed or shifted. V=0 Doppler Effect "Along the line of sight" means the Doppler Effect happens only if the object which is emitting light is moving towards you or away from you. An object moving "side to side" or perpendicular, relative to your line of sight, will not experience a Doppler Effect. Astronomy Application redshift redshift redshift Lecture Tutorial: Doppler Shift (p. 75) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on and write complete thoughts into your LT. If you get stuck or are not sure of your answer, ask me or another group. The Doppler Effect causes light from a source moving away to: be shifted to shorter wavelengths. be shifted to longer wavelengths. change in velocity. Both a and c above Both b and c above You observe two spectra (shown below) that are redshifted relative to that of a stationary source of light. Which of the following statements best describes how the sources of light that produced the two spectra were moving? BLUE RED Source A is moving faster than source B. Source B is moving faster than source A. Both sources are moving with the same speed. It is impossible to tell from looking at these spectra. Spectral Line Analysis The composition of an object is determined by matching its spectral lines with the laboratory spectra of known atoms and molecules. The temperature of an object emitting a continuous spectrum can be measured by matching the overall distribution of radiation with a blackbody curve. The (line-of-sight) velocity of an object is measured by determining the Doppler shift of its spectral lines. An object's rotation rate can be determined by measuring the broadening (smearing out) of its spectral lines. The pressure of the gas in the emitting region of an object can be measured by its tendency to broaden spectral lines. The magnetic field of an object can be inferred from a characteristic splitting it produces in many spectral lines when a single line divides into two (known as the Zeeman effect). Detectors CCDs (charge-coupled devices), much like what is found in your digital cameras, are used to produce images with telescopes (CCD is placed where the eyepiece would normally go). CCDs replaced photographic plates as the standard imaging detector. CCD data is manipulated using various computer software packages. Image Processing Images taken on research quality CCDs are always monochromatic - the colors are added in after the fact. Say you take data through a blue filter (which blocks out all but blue light) and then through a red and green filter. You can assign each image its color and then add the three images to produce a "true color" image. (True color means that's how the object imaged would look if you could view it yourself up close.) Light-Gathering Power A telescope's light-gathering power increases as the square of its diameter. The more light you can gather, the shorter your exposure times. So you use a larger telescope (larger mirror diameter) to observe fainter objects. Resolving Power Resolution - ability to form distinct separate images of objects lying close together in the field of view. The better the resolution, the more detail you can see. In astronomy, we talk about the separation of objects on the sky, or the angular resolution. Atmospheric Blurring Atmospheric turbulence can blur the light from a star (or galaxy, etc.) as the light passes through the atmosphere. Astronomers use the term seeing to describe this blurring effect. The smaller the seeing, the crisper your image. Good seeing means the atmosphere is fairly stable. (Unfortunately, the best seeing often comes along with clouds!) New Telescope Design Two techniques - both used to improve seeing. Active optics - changes the set-up (mirror temperature, airflow, etc.). See below left. Adaptive optics - changes the shape of the mirror (mirror resembles a "honeycomb" shape with many small mirrors making up the primary mirror - each mirror can be moved independently to achieve the best focus). Usually focus telescope using a laser. See below right. The Value of Radio Astronomy Sun is a weak radio source, so radio observations can cover nearly the entire sky. Observations can be made during daytime to within a few degrees of the sun. While visible light can be blocked by gas and dust between us and the object, radio waves usually pass through unaffected. One drawback - usually has poor angular resolution. Interferometry Two or more telescopes are used in tandem to observe the same object at the same time (telescopes combined in such a way are called an interferometer). The effective diameter is equivalent to the distance between the outermost dishes. The larger diameter results in much better angular resolution. Infrared and Ultraviolet Astronomy Infrared telescopes are often optical telescopes used with detectors sensitive to longer wavelengths. There are only a few windows (wavelengths) where IR radiation is not absorbed by the atmosphere. Ultraviolet observations have to be done from space since UV radiation is mostly blocked by Earth's atmosphere. High Energy Astronomy X-ray telescopes are space based. Currently, we have the Chandra X-ray Observatory. Gamma ray telescopes simply count photons received - no image is produced. Image of supernova remnant. Full Spectrum Coverage Full-spectrum coverage is the complete picture, imaging an object at all possible wavelengths. Setting the Scene: Philosophy of the Time The heavens represent perfection. The heavens are immutable. The circle is the perfect shape. All heavenly motions must be circular. The earth is at the center of the universe. These ideas originated with Aristotle. Ptolemy "The astronomer must try his utmost to explain celestial motions by the simplest possible hypothesis; but if he fails to do so, he must choose whatever other hypotheses meet the case." -Ptolemy of Alexandria (140 A.D.) Wanderers in the Heavens Planets don't maintain a fixed position in the sky. Their brightness varies depending on how far away they are from Earth at any time. Planets appear to speed up and slow down in their motion. Planets also appear at times to move backwards, which is known as retrograde motion (normal motion is to move west to east across celestial sphere). F02-01 West East South Ptolemy tried to crate a model that would account for retrograde motion. He placed the planets in orbits (deferents) on orbits (epicycles) all around the Earth. Epicycle Deferent Earth Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Ptolemy's Epicycles Where is retrograde motion occurring? Planet's Path Ptolemy's Epicycles Where is retrograde motion? Planet's Path Planet's Path "A system of this sort seemed neither sufficiently absolute nor sufficiently pleasing to the mind." --Copernicus On the Ptolemaic system: Why heliocentric NOW??? Renaissance: art literature medicine exploration DFY02-01 Copernicus (1473 - 1543 AD) is known for - First sun centered model of the solar system or universe 2. Was a priest and Lawyer Copernicus devised the first comprehensive heliocentric cosmogony to successfully explain retrograde motion DFY02-01 F02-02 Retrograde motion is an apparent motion caused when one planet moves from being behind another planet to being in front of the other planet. "To demonstrate that the appearances are saved by assuming the Sun at the center and the Earth in the heavens is not the same thing as to demonstrate that in fact the Sun is in the center and the Earth in the heavens. I believe that the first demonstration may exist, but I have grave doubts about the second." --Cardinal Bellarmine (1615) Tycho Brahe (1546-1601) - Had artificial wooden and silver noses Rumored to have died when his bladder burst Being the world's best naked-eye astronomer brahe_uburg Tycho Brahe measured distances using parallax that disproved ancient ideas about the heavens He observed a supernova in 1572 and with this showed that the heavens were both changing and had a dimension of distance; this troubled scholars who previously thought the heavens were unchanging. He showed that comets were objects that occurred in the region of the planets, not in Earth's atmosphere. DFY02-02 Johannes Kepler 1571 - 1630 - He was a deeply religious man and a family man. He was rumored to have hated Tycho Brahe and was in the relationship for the data. With that data he changed the understanding of motion of heavenly bodies forever. He was also a writer, who wrote children stories about the heavens. DFY02-02 Johannes Kepler 1571 - 1630 is Known for - Creating first theoretical model to explain planetary motions F02-06a Kepler's First Law: The orbit of a planet about the Sun is an ellipse with the Sun at one focus. kepler_1 Eccentricity, e how squashed or out of round the ellipse is a number ranging from 0 for a circle to 1 for a straight line e = 0.02 e = 0.7 e = 0.9 What is the shape of Earth's orbit around the Sun? Earth, e = 0.016 F02-07 Kepler's Second Law: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time. Second Law Facts A line drawn from the planet to the Sun sweeps out equal areas in equal times orbital speed is not constant for an ellipse only for a circle planets move faster when near the Sun (perihelion) planets move slower when they are far from the Sun (aphelion) Third Law The size of the orbit determines the orbital period planets that orbit near the Sun have shorter periods than planets that are far from the Sun. Kepler's Laws - Lecture Tutorials: Kepler's Second Law (p. 21) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don't understand what the Lecture Tutorial is asking, ask one for help. According to Kepler's second law, a planet with an orbit like Earth's would: move faster when further from the Sun. move slower when closer to the Sun. experience a dramatic change in orbital speed from month to month. experience very little change in orbital speed over the course of the year. none of the above. Which of the following best describes what would happen to a planet's orbital speed if it's mass were doubled but it stayed at the same orbital distance? It would orbit half as fast. It would orbit less that half as fast. It would orbit twice as fast. It would orbit more than twice as fast. It would orbit with the same speed. Kepler's second law says "a line joining a planet and the Sun sweeps out equal areas in equal amounts of time." Which of the following statements means nearly the same thing? Planets move fastest when they are moving toward the Sun. Planets move equal distances throughout their orbit of the Sun. Planets move slowest when they are moving away from the Sun. Planets travel farther in a given time when they are closer to the Sun. Planets move the same speed at all points during their orbit of the Sun. If a small weather satellite and the large International Space Station are orbiting Earth at the same altitude above Earth's surface, which of the following is true? The large space station has a longer orbital period. The small weather satellite has a longer orbital period. Each has the same orbital period. Galileo - 1564-1642 - DFY02-03 Was blind at the time of his death Was labeled a heretic by the church Made first observations of the sun Galileo's Observations Milky Way There are thousands (billions) more stars in the Milky Way than are visible to the naked eye. Universe is bigger than imagined. saturn A Being with Ears The Bulge of Saturn Saturn is not a sphere. Circles and spheres do not dominate the heavens. The Moon The moon has craters. The moon is not a perfect heavenly body. Sunspots The Sun is not a perfect heavenly body. The Sun rotates about its own axis. Galileo's discoveries of the phases of Venus with his telescope showed that Venus must orbit the Sun and strongly supported a heliocentric model Venus is clearly smallest when it is in the full phase and largest when it is in the new phase. Then Venus must be very far from Earth when it is in the full phase and quite close to Earth when in the new phase - which supports the argument that Venus is orbiting the Sun not Earth. Galileo's telescope revealed phases of Venus which could only occur IF Venus orbits the Sun. F02-08 Galileo's telescope revealed that Jupiter had moons which orbited Jupiter instead of Earth. F02-09b F02-09a Isaac Newton (1642 - 1727) is known for - DFY02-04 Creating first theoretical model for explaining gravity and ..... Newton's Three Laws of Motion First Law - A body remains at rest or moves in a straight line at a constant speed unless acted upon by an outside (net) force. Second Law - (net) Force = mass x acceleration Third Law - Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body. Newton's Law of Gravitation Newton's law of gravitation states: Two bodies attract each other with a force that is directly proportional to the product of their masses and is inversely proportional to the square of the distance between them. Newton's Laws and Kepler's Laws Newton's law of gravitation and his three laws of motion prove all of Kepler's laws. Gravity and Newton's Laws - Lecture Tutorial (p. 29) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don't understand what the Lecture Tutorial is asking, ask for help. Which of the following forces is strongest? The force you exert on the earth. The force the earth exerts on you. This is a trick question: the force you exert on the earth is identical in strength to the force the earth exerts on you. The Circle of Scientific Progress The progression from the complex Ptolemaic model of the universe to Newton's laws is an example of the scientific method in use (the model was changed until it met the observations and made correct predictions).