Astronomy set 2 honors – Flashcards

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Which of the following correctly lists our "cosmic address" from small to large?
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Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe
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An astronomical unit is
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Earth's average distance from the Sun
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Rank the following items according to their size (diameter) from left to right, from largest to smallest
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universe, local supercluster, local group, Milky Way, solor system, Sun, Jupiter, Earth
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Rank the following items that describe distances from longest distance (left) to shortest distance (right).
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Milky Way to Andromeda, Sun to Milky Way, Earth to Alpha Centauri, Orion Nebula, one light-year, distance across our solor system, AU
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If we represent the solar system on a scale that allows us to walk from the Sun to Pluto in a few minutes, then:
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the planets would all be marble size or smaller and the nearest stars would be thousands of miles away.
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The age of the current universe is about:
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14 billion years.
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Could we see a galaxy that is 50 billion light-years away?
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No, because a galaxy could not possibly be that far away.
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The star Betelgeuse is about 600 light-years away. If it explodes tonight,
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we won't know about it until 600 years from now.
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How long in seconds does it take light to travel from the Moon to Earth?
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1.28 s
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How long in seconds does it take light to travel from the Sun to Earth?
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499 s
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How old is the age of our solar system?
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one-third of the age of the universe.
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On the cosmic calendar, which compresses the history of the universe into a single year, about when did Earth form?
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in early September
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In winter, Earth's axis points toward the star Polaris. In spring:
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the axis also points toward Polaris
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The North Celestial Pole is 35.0 ∘ above your northern horizon. This tells you that:
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you are at latitude 35.0 ∘ N.
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When it is summer in Australia, the season in the United States is
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winter.
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Which of the following has a latitude of 23½ N?
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the Tropic of Cancer
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Which of the following has a latitude of 23½ S?
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the Tropic of Capricorn
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Which of the following has a latitude of 0?
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the Equator
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Which of the following has a latitude of 66½ N?
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Arctic Circle
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Which of the following has a latitude of 90 N?
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North Pole
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The Summer Solstice occurs in the Northern Hemisphere when the Sun is directly overhead
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the Tropic of Cancer 23½ N.
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The Summer Solstice occurs in the Southern Hemisphere when the Sun is directly overhead
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the Tropic of Capricorn 23½ S
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The Winter Solstice occurs in the Southern Hemisphere when the Sun is directly overhead
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the Tropic of Cancer 23½ N
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The Winter Solstice occurs in the Northern Hemisphere when the Sun is directly overhead
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the Tropic of Capricorn 23½ S
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The Winter Solstice in the Southern Hemisphere occurs on
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June 21 - 22
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The Vernal Equinox in the Northern Hemisphere occurs on
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March 21 - 22
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The Autumnal Equinox in the Southern Hemisphere occurs on
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March 21 - 22
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If the Sun rises precisely due east:
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it must be the day of either the spring or fall equinox.
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Waxing Crescent
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visible near wester horizon about an hour after sunset sets 2-3 hours after the Sun sets
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Waning Crescent
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visible near easter horizon just before sunrise occurse about 3 days before new moon
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Full Moon
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occurs 14 days after the new moon rises at about the time the Sun sets visible due south at midnight
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The phase of the Moon
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is the same for all observers over the Earth's surface. is caused by sunlight reflected off the Moon's surface.
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A week after full moon, the Moon's phase is:
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third quarter
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A full moon
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rises at sunset. is high in the sky at midnight sets at dawn. is approximately the opposite direction in the sky to the Sun.
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A solar eclipse can occur
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only at new moon. only during daytime when the Moon passes between the Earth and the Sun
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A lunar eclipse can occur
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only at full moon. only at night. when the Earth passes between the Moon and the Sun.
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A lunar eclipse can be seen
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by all observers on the nighttime side of Earth.
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What conditions are required for a lunar eclipse?
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The phase of the Moon must be full, and the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun.
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A total solar eclipse can be seen
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only by observers in a narrow band on the daytime side of the Earth's surface.
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A solar eclipse viewed from Earth can be total because when viewed from the Earth's surface
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the Sun and the Moon have approximately the same angular size.
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What is the ecliptic?
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the path the Sun appears to trace around the celestial sphere each year
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When we see Saturn going through a period of apparent retrograde motion, it means
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Earth is passing Saturn in its orbit, with both planets on the same side of the Sun.
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What do astronomers mean by a constellation?
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A constellation is a region in the sky as seen from Earth.
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How many arcminutes are in a full circle?
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21,600
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1.296×106
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1,296,000
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The Moon's angular size is about 1/2∘. What is this in arcminutes?
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30.0 arcminutes
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The Moon's angular size is about 12∘. What is this in arcseconds?
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1800 arcseconds
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Stars that are visible in the local sky on any clear night of the year, at any time of the night, are called
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circumpolar
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What is stellar parallax
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It is the slight back-and-forth shifting of star positions that occurs as we view the stars from different positions in Earth's orbit of the Sun.
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How would a star's parallax change as its distance from Earth increases
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The parallax shift decreases as the star's distance from Earth increases
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Keplar's first law
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The orbit of a planet is an ellipse with the Sun at one of the two foci.
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Keplar's Second Law
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A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
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Keplar's Third Law
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The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.
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The point along a planet's orbit where it is closest to the Sun is called the orbit's
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perihelion.
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Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler's second law:
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Earth travels faster in its orbit around the Sun in January than in July.
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Jupiter orbits the Sun at an average distance of 5.203 AU and takes 11.86years to complete each orbit. Based on these facts, which statement is true?
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11.86^2=5.203^3
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You discover an asteroid that orbits the Sun with the same 1-year orbital period as Earth. Which of the following statements must be true?
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The asteroid's average (semimajor axis) distance from the Sun is 1AU
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All of the following statements are true. Which one can be explained by Kepler's third law?
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Venus orbits the Sun at a faster orbital speed than Earth.
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According to Kepler's third law (p2 = a3), how does a planet's mass affect its orbit around the Sun?
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A planet's mass has no effect on its orbit around the Sun.
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All the following statements are true. Which one follows directly from Kepler's third law (p 2 = a 3)?
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Venus orbits the Sun at a slower average speed than Mercury.
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From Kepler's third law, an asteroid with an orbital period of 8 years lies at an average distance from the Sun equal to
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4 astronomical units
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Suppose a comet orbits the Sun on a highly eccentric orbit with an average (semimajor axis) distance of 1 AU. How long does it take to complete each orbit, and how do we know?
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Each orbit takes about 1 year, which we know from Kepler's third law.
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The Earth is instantly replaced in its orbit by a speck of dust. Which statement best describes the subsequent orbital motion of that piece of dust?
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The dust particle will continue in the same orbit as the Earth did, orbiting the Sun in 1 year.
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He discovered what we now call Newton's first law of motion.
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Galileo
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You want to test how the mass of a ball affects its rate of fall. Which of the following ball drop trials (matched mass and drop heights) would best test this question?
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Mass of 0.5 kg, height 20 m; mass of 5.0 kg, height 20 m
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HOW WE SEE THE UNIVERSE
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> light and other electromagnetic radiation >other particle radiation (eg electrons) >meteorites, rock samples, dust >objects in the same direction when observed from Earth in general are not close to each other or interacting with each other
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Dark may mean
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• 1. nothing there or • 2. something there but not emitting or • 3. something in path absorbing the light
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• in Earth lab we can't investigate
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ultrahigh temperatures, ultra-strong gravity, gravity over very large distances, effect of very long times
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Astronomical Unit (AU)
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average distance between Earth and Sun = 150 million km
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Light Year
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distance light travels in one year = 9.5 x 1012 km = 63,000 AU
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Light from the Sun takes about
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8 minutes to reach Eart
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Moon
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300,000 km or 1 light-second away
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Sun 1 AU
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8 min 20 seconds away
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Pluto about 39 AU
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5 light-hours away
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Heliopause 90 AU
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13 light-hours away
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edge of the Solar System
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100,000 AU or ~ 1.5 light-year away
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nearest star visible with naked eye α-Centauri
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275,000 AU or ~ 4.3 light years away
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Solar system and Earth
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4.6 - 5 billion years old
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Universe
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13.8 billion years old
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EARTH'S SPIN AXIS
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today axis is 23½° to the perpendicular to plane of Earth's orbit around the Sun • today axis points toward Polaris (the North Star) • direction of axis precesses with 26,000 year cycle • direction of axis nutates between about 22° - 24½° with 42,000 year cycle
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SOLSTICES
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June 21/22 Sun overhead Tropic of Cancer (23½ º N latitude) midsummer in northern hemisphere and midwinter in southern hemisphere • December 21/22 Sun overhead Tropic of Capricorn (23½ º S) midwinter in northern hemisphere and midsummer in southern hemisphere
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EQUINOXES
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Sun overhead at Equator (0º latitude) • equal 12 hrs daylight, 12 hrs night everywhere on Earth • Sun rises due east and sets due west • March 21/22 and September 22/23 (Autumnal and Vernal)
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sidereal day
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time Earth spins until stars appear again in same positions on sky; ~ 23 hr 56 min;
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solar day
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time Earth spins until Sun appears again in same position on sky; ~ 24 hours (longer than sidereal day)
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year
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time until Sun appears in same position relative to fixed stars as seen by observer on Earth; 365 ¼ solar days
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New Moon
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sunlit portion of Moon faces away from Earth • Sun and Moon in same direction from Earth • New Moon rises at dawn with Sun and sets at sunset • Crescent Moon when near New Moon
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Full Moon
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• sunlit portion of Moon faces Earth • Sun and Moon in opposite directions from Earth • Full Moon rises at sunset and sets at dawn • Gibbous Moon when near Full Moon
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First Quarter (Waxing Moon)
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• rises at noon and sets at midnight
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Third Quarter (Waning Moon)
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• rises at midnight and sets at noon
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Sidereal Month
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• period of Moon's revolution around Earth • 27 1/3 days
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Synodic Month
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• period for Moon to cycle through phases as viewed from Earth • greater than sidereal month because meanwhile Earth is moving around Sun • 29 ½ days • Moon rises 50 minutes later each night
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LUNAR DAY
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• 27 1/3 Earth days • any place on Moon's surface has ~ 2 weeks daylight then 2 weeks night • equals sidereal month same face of Moon always points toward Earth Moon is tidally locked to Earth (originally Moon rotated faster but Earth's tidal pull slowed Moon's rotation)
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LUNAR ORBIT
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• plane of lunar orbit inclined at 5 ° to plane of Earth's orbit around Sun (ecliptic plane) • nodes = point(s) where lunar orbit plane intersects ecliptic plane • orientation of lunar orbit stays fixed relative to fixed stars nodes move relative to Earth as Earth goes around Sun
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ECLIPSES
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one body passes through shadow of another body • by coincidence angular size of Sun as seen from Earth roughly equals angular size of Moon as seen from Earth (both about 0.5°) • occurs when Earth, Sun and Moon are aligned (syzygy) and Moon is at or near node • Moon Earth Sun aligned at node about twice a year lunar eclipse at Full Moon and solar eclipse at New Moon about twice a year (typically 4 eclipses per yr but can be up to 7) • Saros Cycle - eclipse cycle repeats every 18 yr 11 1/3 days (but solar eclipses not visible at the same place on Earth each time)
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umbra
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dark shadow see Total Eclipse
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penumbra
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shadow not as dark (because some light bent in Earth's atmosphere
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LUNAR ECLIPSE
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• Earth moves between Sun and Moon • Moon moves through Earth's shadow • can only happen at Full Moon (during nighttime on Earth) • can be seen by everyone on nighttime side of Earth, totality last ~ 1 hour • Moon looks red (red light is scattered less than blue light in Earth's atmosphere)
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• Total Lunar Eclipse
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whole of Moon moves through umbra
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• Partial Lunar Eclipse
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part of Moon moves through umbra
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Penumbra Lunar Eclipse =
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Moon moves through penumbra only
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SOLAR ECLIPSE
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• Moon is between Earth and Sun; Earth moves through Moon's shadow • can only happen at New Moon (during daylight on Earth) • Total Solar Eclipse = observer in Moon's umbra • Partial Solar Eclipse = observer in Moon's penumbra • Annular Solar Eclipse = Moon's umbra doesn't reach Earth
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Path of Totality
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• total eclipse only seen by people in narrow (< 275 km) path of umbra on Earth's surface • in path see Moon move across Sun sky darkens at totality sharp drop in temperature see Sun's outer atmosphere (chromosphere) totality lasts less than about 7 minutes Sun gradually becomes visible again
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EARTH-MOON SYSTEM
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• Earth's rotation rate has been slowing over time + Moon has been gradually moving further away from Earth + lunar month has been gradually lengthening due to Moon's and Sun's tidal friction on Earth • day ~ 11 hours 2.5 Gya • day ~ 21 hours 500 Mya • day = 24 hours today • Moon formed at 20,000 km from center of Earth, today at 384,000 km from Earth
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PLANETS
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• see disk, doesn't twinkle like a star, moves relative to background stars • along ecliptic • usually move eastward relative to background stars • Retrograde Motion - occasionally planet appears to move in opposite direction • planets orbiting between Earth and Sun never reach overhead (zenith) at night when viewed from Earth : Mercury's maximum elevation is 28°, Venus's is 47° • Conjunction = planet and Sun are aligned when viewed from Earth (Earth+Sun+planet or Earth+planet+Sun in line) • Opposition = planet is in opposite direct to Sun when viewed from Earth (only can happen if planet's orbit is beyond Earth's orbit)
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OBSERVING STARS
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• Celestial Sphere • Celestial Equator = extension of Earth's equator on sky • Celestial North and South Poles = extension of Earth's polar axis on sky • Horizon • Zenith = directly overhead • Meridian = North-South Line thru zenith • Celestial Equator, Celestial Poles • Horizon, Zenith, Meridian • Azimuth = direction along horizon from North • Altitude = elevation above horizon • to measure angular size of non-pointlike object or angular distance between objects • 1° = 60 arc minutes = 60' • 1' = 60 arc seconds = 60'' • Stretch out your arm hand span ~20°, finger width ~ 1°, closed fist ~10° Note: angular size or angular distance does not equal real size or distance (which is angle times distance to object(s) from Earth) • stars rise in easterly direction and set in westerly direction (rise 4 minutes earlier each night) • near North Celestial Pole, circumpolar stars don't set but move anticlockwise about North Star (Polaris) • altitude of North Celestial Pole (Polaris Angle) = latitude of your location on Earth • in Jacksonville never see stars near South Celestial pole
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Ecliptic
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Sun (and planets) moves along ecliptic from point of view of observer on Earth
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Zodiac
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Constellations along Ecliptic
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Constellation
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group of stars near each other on sky as seen by observer on Earth - may or may not be near each other in space
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PRE-HISTORY ASTRONOMY
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• marking seasons (preparing for winter, seasonal floods and droughts, hunting and gathering, agriculture) may have been more important at mid- and high latitudes • daily time-keeping eg sundials or something with regular motion or regular change • 'magical' power of prediction (eclipses, lunar calendar), prediction often conferred political power • navigation over land and sea • end of last glacial period ~ 13,000 - 11,500 yrs ago • Pleistocene-Holocene impact(s)?
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EVIDENCE?
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• rock, cave and other art • buildings/structures eg astronomical alignments in woodhenges and stonehenges? • folk stories, myths, legends, early religious texts eg Old Testament look for stories whose basic characteristics match natural astronomical or climatic or geophysical events even if embellishments or interpretations in story seem fanciful, look for same event appearing in multiple stories or sources
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Aristarchus (~260BC)
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proposed Earth is spherical and rotates on its axis and revolves around the Sun; noted Moon shines by reflected sunlight; deduced distances to Moon and Sun in Earth radii (from eclipse geometry) Eratosthenes (~240BC) calculated Earth's radius by comparing difference in Sun's altitude at two different latitudes
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Hipparchus
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- early star catalog
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Planetary Motion
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most Greek models had planets orbitting Earth (Aristotle (geocentric world view) and Plato (perfect motion is circular))
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Ptolemaic Model (100AD)
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geocentric planetary orbits + epicycles to explain planet retrograde motion
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Nicholas Copernicus (1473 - 1543 AD)
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• Sun-centered model but used circular orbits • planets go around the Sun in circle orbits • used difference between synodic and sidereal period to find distance between planet and Sun
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Tycho Brache (1546 - 1601 AD)
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• 30 years of systematic naked-eye observations of planets, moons, stars
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Johannes Kepler (1571 - 1630 AD)
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• mathematically analyzed Tycho Brache's data Kepler's Laws of Planetary Motion
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KEPLER'S FIRST LAW
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The orbit of each planet is an ellipse with the Sun at one focus
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Perihelion
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closest point in orbit to Sun
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Aphelion
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farthest point in orbit from Sun
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KEPLER'S SECOND LAW
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The line from a planet to the Sun sweeps out equal area in equal times as the planet orbits around the Sun planet moves faster when it is closer to the Sun planet moves slower when it is further away from the Sun
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KEPLER'S THIRD LAW
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The square of a planet's orbital period (P) is directly proportional to the cube of the average distance (A) between the planet and the Sun P^2 = A^3 when write P in Earth years and A (the semimajor axis of the orbital ellipse) in AU planets closer to the Sun have shorter 'years' planets further from the Sun have longer 'years'
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GALILEO
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bolstered Copernicus and Kepler with observations made using telescopes (eg observed phases of Venus which proved Venus orbits Sun) • experimentally showed by dropping objects off a tall building that all objects at the same location are accelerated at the same rate by a gravitational force • deduced that an object moves at constant velocity if not acted on by external agent
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Acceleration
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= rate of change of velocity ie rate of change of speed and/or velocity's direction • gravitational acceleration at Earth's surface is 9.8 ms‐2 directed toward center of Earth • orbiting planet continuously changes its direction so planet must be acceleratin
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Momentum
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mass x velocity Momentum and force have a magnitude and a direction Momentum of body changes only if body is acted on by net force
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Force
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mass x acceleration
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Mass
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is amount of matter ('weight' is force of gravity acting on mass on weighing scales)
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Four Fundamental Forces of Nature
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Gravity Electric/magnetic Force Strong Nuclear Force Weak Nuclear Force • gravity is most important force on large scales (Universe is electrically neutral on large scales) • strong and weak nuclear forces are important in stars and the Early Universe
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Other Macroscopic Forces
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friction, drag, push, pull
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FIRST LAW
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If no net force acts on a body, body will continue to move with constant velocity or remain at rest A free object in the Universe moves in a straight line
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SECOND LAW:
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Net force acting on body = mass of body x acceleration of body = rate of change of body's momentum Orbiting planet is accelerating and so must be acted on by force momentum is conserved if net force on body is zero
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THIRD LAW:
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Any force is always accompanied by an equal and opposite reaction force (of same magnitude but opposite direction) Sun pulls on planet and planet pulls equally on Sun Fire the back engine of rocket to make rocket move forward
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Angular Momentum = m r v
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where r is distance from focus of orbit to body of mass m and velocity v
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Torque = r F
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if force F is perpendicular to r
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Torque = 0
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if force F is parallel to r
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Conservation of Angular Momentum:
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angular momentum is conserved if net torque on body is zero
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m r v = constant for a given planet in its orbit
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(because the force of gravity is always perpendicular to planet's velocity and so torque is zero)
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when r is small, v is large
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(ie planet moves faster when closer to Sun)
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when r is large, v is smal
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l (ie planet moves slower when further from Sun)
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Conservation of Energy
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can't create or destroy energy, can only change from one form to another
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kinetic energy
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energy of motion E = ½ mv2
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radiative energy
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E µ f µ 1/λ (where f is frequency, λ is wavelength of light)
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mass energy
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E = mc2
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potential energy
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(which can be converted to kinetic or radiative energy) eg energy stored in battery or energy stored in gravitational field (gravitational potential energy depends on location in gravitational field)
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Thermal Energy
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kinetic energy of many particles eg gas particles
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Temperature
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average kinetic energy per particle
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FORCE OF GRAVITY
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• inverse square law; measure distance d from center of mass M • stronger if decrease separation or if larger mass; weaker if increase separation or if smaller mass • always attractive, points towards other body
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Gravitational Potential Energy
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eg released as kinetic energy or heat as giant gas cloud collapses under its own gravity (ie when d decreases) • eg rocket must supply potential energy to overcome gravity when launched off planet
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• Kepler 1:
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Newton mathematically showed bound orbits (of planets, moons, satellites) are ellipses and unbound orbits are parabolae and hyperbolae
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Kepler 2:
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conservation of angular momentum
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Kepler 3
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P2 µ A3 from equations (observe orbits and use to determine mass of binary stars etc)
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Free‐Falling
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= falling in gravitational field eg cut cable in elevator • Planets are free‐falling toward Sun • Space Shuttle in orbit is free‐falling towards Earth (makes astronaut feel weightless relative to Shuttle but astronaut is still accelerating in Earth's gravitational field)
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Total Orbital Energy = Kinetic Energy + Gravitational Potential Energy
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• Total orbital energy is constant if object is not disturbed (ie orbiting object can't spontaneously change orbit) must fire rocket engine to boost orbital energy and move rocket into different orbit • gravitational encounter with another object can disturb orbit eg Jupiter's gravity can change comet's orbit around Sun • atmospheric drag (friction due to air particles) can cause satellite to lose energy and its orbit to decay (so need to fire booster engines to maintain orbit)
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ESCAPE VELOCITY
ESCAPE VELOCITY
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minimum launch velocity an object must have to reach an infinite distance from the planet (ie to escape to Deep Space)
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Low Earth Orbit (LEO)
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• 160 ‐ 2,000 km above Earth's surface • speed 27,000 km/h • orbital period 90 minutes - 2 hours • eg International Space Station (386 km)
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Medium Earth Orbit (MEO or ICO)
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• 2,000 ‐ 36,000 km above Earth's surface • speed 11,000 ‐ 27,000 km/h • orbital period 2 - 24 hours • eg GPS
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Geostationary Orbit (GEO)
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stays above fixed point on Earth's surface orbital period = 24 hours • must be in equatorial plane • 36,000 km above Earth's surface • speed 11,000 km/h • eg TV satellites
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Geosynchronous Orbit
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• orbital period = 24 hours • 36,000 km above Earth's surface • if orbit is tilted satellite will not be geostationary
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Launch
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• currently requires about 30kg of fuel (and $10,000) to launch 1 kg of payload into LEO • save fuel and money by launching in eastward direction to take advantage of rotational speed of Earth (1,700 km/h at equator) • ideally launch over ocean for safety About 3,000 satellites in orbit about Earth
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TIDES
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tides and tidal stress are due to the difference in gravity felt at two different locations
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Moon
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• water bulges on side of Earth closest to Moon (pull strongest) + water bulges away on other side of Earth (pull weakest) solid Earth rotates through two tidal bulges usually 2 high tides and 2 low tides each day
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Spring Tide
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= high tide increased when Earth + Moon + Sun roughly aligned ‐ occurs twice a month
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Neap Tide
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high tide decreased when Moon at right angles to Sun ‐ occurs twice a month
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TIDAL FRICTION
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• gradually slows Earth spin (day was much shorter early in Earth's history) and slightly increases distance between Moon and Earth (increasing lunar period) • slowed down Moon's spin so that now same face of Moon always faces Earth
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Wavelength λ
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distance between 2 crests or 2 troughs
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Frequency f =
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= number of crests passing per unit time
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Speed of Light
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constant = 3 x 108 m s-1 = wavelength x frequency
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• Energy of Light
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increases as frequency increases or wavelength decreases
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ATOM
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• n neutrons + p protons + e electrons • nucleus = n + p • electric force between p and e; strong and weak nuclear forces between n and p • number of p determines chemical species • number of p and n determines mass and atomic mass number • chemical interactions and bonds in molecules (compounds of 2 or more atoms) involve electrons
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isotope
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same number of p, different number of n
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radioactive
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unstable combination of p+n in nucleus
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electrons
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• electrons in atom can only have certain energies • electron can move between energy levels only if it absorbs or emits light of the precise wavelength which matches the energy difference electron moves up in energy level if it absorbs light of the precise wavelength; electron moves down in energy level if it emits light of the precise wavelength • if electron gains enough energy to escape atom, call the atom an ion which has been ionized
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• continuous spectrum
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m (eg thermal emission from warm body)
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emission lines
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at specific wavelengths (bright lines)
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absorption lines
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at specific wavelengths (dark lines in spectrum)
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THERMAL RADIATON
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• emitted by every object with a temperature T greater than 0°K
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Stefan-Boltzmann Law:
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Each square meter of a hotter object radiates more light at all wavelengths than a colder object ( µ T 4 )
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Wien's Law:
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Hotter objects emit light with a higher average energy ie radiation from a hotter object peaks at a shorter wavelength and higher frequency
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DOPPLER SHIFT
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• approaching object's light is 'blueshifted' to shorter wavelength (and higher frequency) • receding object's light is 'redshifted' to longer wavelength (and lower frequency)
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Light-collecting area:
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• determines how much light from a source is captured by telescope determines faintest object telescope can see • increases as square of diameter eg 10m telescope collects 25 times more light than 2m telescope
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Angular resolution
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= smallest angular separation between 2 objects on sky which telescope can still resolve as 2 distinct objects • larger telescopes have higher resolution (goes as diameter) • theoretically limited by diffraction; resolution weakened by Earth's atmosphere • Hubble Space Telescope: usually 0.05'' in visible; up to 0.007'' in UV
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Magnification
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• goes as diameter of telescope larger telescopes have greater magnification
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REFRACTING TELESCOPE
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• uses glass lenses to collect and focus light • place eye or detector (camera, CCD, spectrograph) at focus of lens system • hard to support very large lenses; chromatic aberration
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REFLECTING TELESCOPE
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• uses large curved primary mirror to collect and smaller secondary curved mirror to focus light • largest telescopes today are reflectors
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INTERFEROMETER
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• mirror in segments separated by distance • increased angular resolution but lightcollecting power unchanged • radio telescopes up to microarcsecond resolution • optical and near-IR measurements up to milliarcsecond resolution • can also use change in position of mirror segment due to Earth's rotation and revolution
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GROUND-BASED TELESCOPES
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• ability to observed light is affected by atmospheric turbulence and absorption
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Best Sites for Submillimeter, Infrared and Visible Telescopes:
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• mountain tops, above clouds and water vapor • away from light pollution • good year-round weather
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Adaptive Optics:
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• to cancel out atmospheric distortions which cause stars to 'twinkle'
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Radio:
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• long wavelengths so need very large 'mirror' (metal antenna); ground-based telescopes • stars, galaxies, pulsars, cool hydrogen gas
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Microwave:
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• upper atmosphere or space-based telescopes • relic Big Bang radiation
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Infrared:
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• spaced-based and ground-based telescopes (limited by water vapor in Earth's atmosphere) • cold gas clouds, dust, protostars, very distant redshifted galaxies
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Visible:
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• ground-based and space-based telescopes
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Ultraviolet:
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• space-based telescopes • hot young massive stars or very old stars and galaxies near end of their life, hot interstellar gas, chemical evolution of galaxies
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X-ray:
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• space-based and balloon telescopes • neutron stars, black holes, very hot gases, active galactic nuclei, quasars, galactic jets
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Gamma-ray:
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• space-based and balloon telescopes • gamma ray bursts (most are the collapse of very large stars at great distances from Earth)
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Ultra-High Energy:
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• light and other particles • very large ground-based telescopes detect interaction of ultra-high energy particles with Earth's atmosphere
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Einstein 1905:
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• speed of light c = 3 x 10 8 ms-1 for all inertial (non-accelerating) observers • Laws of Physics are the same for all inertial observers • mass is also energy E = mc 2 • no object with mass can travel at the speed of light (takes infinite energy for massive object to reach c) • length contraction, time dilation
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Length Contraction:
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• object appears longest to observer at rest relative to object • object appears shorter to moving observer
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Time Dilation:
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• time interval between events increases for observer moving relative to events
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What is our place in the universe?
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Easrth is a planet orbiting the Sun. Our Sun is one of more than 100 billion stars in the Milky Way Galaxy. Our galaxy is one of more than 70 galaxies in the Local Group. The Local Group is part of the Local Supercluster, which is one small part of the universe.
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How big is the universe?
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If the Sun is as large as a grapefruit, Earth is a ballpoint that orbits 15 meters away; the nearest stars are thousands of kilometers away. Our galaxy contains 100 billion stars. The observable universe contains 100 billion galaxies and the total number of stars is comparable to the number of grains of dry sand on all the beaches of earth.
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How did we come to be?
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The Big Bang happened and the universe is constantly expanding except in localized regions where gravity has caused matter to collapse into galaxies and stars. The Big Band produced hydrogen and helium. The other elements are produced by stars and recycled within galaxies from one generation of stars to the next.
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Ho do our lifetimes compare to the age of the universe
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The cosmic clendar that compresses the history of the universe into 1 year, humans are just a few seconds old.
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How is Earth moving through space?
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Earth rotates on its axis once each day and orbits the Sun once a year. At the same time, we move with our Sun in random directions relative to other stars in our local solar neighborhood, while the galaxy's rotation carries us around the center of the galaxy every 230 million years.
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How do galaxies move within the universe?
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Galaxies move essentially at random within the Local Group, but all galaxies beyond the Local Group are moving away from us. More distant galaxies are moving faster, which tells us that we live in an expanding universe.
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