question

Which of the following correctly lists our "cosmic address" from small to large?

answer

Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe

question

An astronomical unit is

answer

Earth's average distance from the Sun

question

Rank the following items according to their size (diameter) from left to right, from largest to smallest

answer

universe, local supercluster, local group, Milky Way, solor system, Sun, Jupiter, Earth

question

Rank the following items that describe distances from longest distance (left) to shortest distance (right).

answer

Milky Way to Andromeda, Sun to Milky Way, Earth to Alpha Centauri, Orion Nebula, one light-year, distance across our solor system, AU

question

If we represent the solar system on a scale that allows us to walk from the Sun to Pluto in a few minutes, then:

answer

the planets would all be marble size or smaller and the nearest stars would be thousands of miles away.

question

The age of the current universe is about:

answer

14 billion years.

question

Could we see a galaxy that is 50 billion light-years away?

answer

No, because a galaxy could not possibly be that far away.

question

The star Betelgeuse is about 600 light-years away. If it explodes tonight,

answer

we won't know about it until 600 years from now.

question

How long in seconds does it take light to travel from the Moon to Earth?

answer

1.28 s

question

How long in seconds does it take light to travel from the Sun to Earth?

answer

499 s

question

How old is the age of our solar system?

answer

one-third of the age of the universe.

question

On the cosmic calendar, which compresses the history of the universe into a single year, about when did Earth form?

answer

in early September

question

In winter, Earth's axis points toward the star Polaris. In spring:

answer

the axis also points toward Polaris

question

The North Celestial Pole is 35.0 ∘ above your northern horizon. This tells you that:

answer

you are at latitude 35.0 ∘ N.

question

When it is summer in Australia, the season in the United States is

answer

winter.

question

Which of the following has a latitude of 23½ N?

answer

the Tropic of Cancer

question

Which of the following has a latitude of 23½ S?

answer

the Tropic of Capricorn

question

Which of the following has a latitude of 0?

answer

the Equator

question

Which of the following has a latitude of 66½ N?

answer

Arctic Circle

question

Which of the following has a latitude of 90 N?

answer

North Pole

question

The Summer Solstice occurs in the Northern Hemisphere when the Sun is directly overhead

answer

the Tropic of Cancer 23½ N.

question

The Summer Solstice occurs in the Southern Hemisphere when the Sun is directly overhead

answer

the Tropic of Capricorn 23½ S

question

The Winter Solstice occurs in the Southern Hemisphere when the Sun is directly overhead

answer

the Tropic of Cancer 23½ N

question

The Winter Solstice occurs in the Northern Hemisphere when the Sun is directly overhead

answer

the Tropic of Capricorn 23½ S

question

The Winter Solstice in the Southern Hemisphere occurs on

answer

June 21 - 22

question

The Vernal Equinox in the Northern Hemisphere occurs on

answer

March 21 - 22

question

The Autumnal Equinox in the Southern Hemisphere occurs on

answer

March 21 - 22

question

If the Sun rises precisely due east:

answer

it must be the day of either the spring or fall equinox.

question

Waxing Crescent

answer

visible near wester horizon about an hour after sunset sets 2-3 hours after the Sun sets

question

Waning Crescent

answer

visible near easter horizon just before sunrise occurse about 3 days before new moon

question

Full Moon

answer

occurs 14 days after the new moon rises at about the time the Sun sets visible due south at midnight

question

The phase of the Moon

answer

is the same for all observers over the Earth's surface. is caused by sunlight reflected off the Moon's surface.

question

A week after full moon, the Moon's phase is:

answer

third quarter

question

A full moon

answer

rises at sunset. is high in the sky at midnight sets at dawn. is approximately the opposite direction in the sky to the Sun.

question

A solar eclipse can occur

answer

only at new moon. only during daytime when the Moon passes between the Earth and the Sun

question

A lunar eclipse can occur

answer

only at full moon. only at night. when the Earth passes between the Moon and the Sun.

question

A lunar eclipse can be seen

answer

by all observers on the nighttime side of Earth.

question

What conditions are required for a lunar eclipse?

answer

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.

question

A total solar eclipse can be seen

answer

only by observers in a narrow band on the daytime side of the Earth's surface.

question

A solar eclipse viewed from Earth can be total because when viewed from the Earth's surface

answer

the Sun and the Moon have approximately the same angular size.

question

What is the ecliptic?

answer

the path the Sun appears to trace around the celestial sphere each year

question

When we see Saturn going through a period of apparent retrograde motion, it means

answer

Earth is passing Saturn in its orbit, with both planets on the same side of the Sun.

question

What do astronomers mean by a constellation?

answer

A constellation is a region in the sky as seen from Earth.

question

How many arcminutes are in a full circle?

answer

21,600

question

1.296×106

answer

1,296,000

question

The Moon's angular size is about 1/2∘. What is this in arcminutes?

answer

30.0 arcminutes

question

The Moon's angular size is about 12∘. What is this in arcseconds?

answer

1800 arcseconds

question

Stars that are visible in the local sky on any clear night of the year, at any time of the night, are called

answer

circumpolar

question

What is stellar parallax

answer

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.

question

How would a star's parallax change as its distance from Earth increases

answer

The parallax shift decreases as the star's distance from Earth increases

question

Keplar's first law

answer

The orbit of a planet is an ellipse with the Sun at one of the two foci.

question

Keplar's Second Law

answer

A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

question

Keplar's Third Law

answer

The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

question

The point along a planet's orbit where it is closest to the Sun is called the orbit's

answer

perihelion.

question

Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler's second law:

answer

Earth travels faster in its orbit around the Sun in January than in July.

question

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?

answer

11.86^2=5.203^3

question

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?

answer

The asteroid's average (semimajor axis) distance from the Sun is 1AU

question

All of the following statements are true. Which one can be explained by Kepler's third law?

answer

Venus orbits the Sun at a faster orbital speed than Earth.

question

According to Kepler's third law (p2 = a3), how does a planet's mass affect its orbit around the Sun?

answer

A planet's mass has no effect on its orbit around the Sun.

question

All the following statements are true. Which one follows directly from Kepler's third law (p 2 = a 3)?

answer

Venus orbits the Sun at a slower average speed than Mercury.

question

From Kepler's third law, an asteroid with an orbital period of 8 years lies at an average distance from the Sun equal to

answer

4 astronomical units

question

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?

answer

Each orbit takes about 1 year, which we know from Kepler's third law.

question

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?

answer

The dust particle will continue in the same orbit as the Earth did, orbiting the Sun in 1 year.

question

He discovered what we now call Newton's first law of motion.

answer

Galileo

question

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?

answer

Mass of 0.5 kg, height 20 m; mass of 5.0 kg, height 20 m

question

HOW WE SEE THE UNIVERSE

answer

> 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

question

Dark may mean

answer

• 1. nothing there or • 2. something there but not emitting or • 3. something in path absorbing the light

question

• in Earth lab we can't investigate

answer

ultrahigh temperatures, ultra-strong gravity, gravity over very large distances, effect of very long times

question

Astronomical Unit (AU)

answer

average distance between Earth and Sun = 150 million km

question

Light Year

answer

distance light travels in one year = 9.5 x 1012 km = 63,000 AU

question

Light from the Sun takes about

answer

8 minutes to reach Eart

question

Moon

answer

300,000 km or 1 light-second away

question

Sun 1 AU

answer

8 min 20 seconds away

question

Pluto about 39 AU

answer

5 light-hours away

question

Heliopause 90 AU

answer

13 light-hours away

question

edge of the Solar System

answer

100,000 AU or ~ 1.5 light-year away

question

nearest star visible with naked eye α-Centauri

answer

275,000 AU or ~ 4.3 light years away

question

Solar system and Earth

answer

4.6 - 5 billion years old

question

Universe

answer

13.8 billion years old

question

EARTH'S SPIN AXIS

answer

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

question

SOLSTICES

answer

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

question

EQUINOXES

answer

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)

question

sidereal day

answer

time Earth spins until stars appear again in same positions on sky; ~ 23 hr 56 min;

question

solar day

answer

time Earth spins until Sun appears again in same position on sky; ~ 24 hours (longer than sidereal day)

question

year

answer

time until Sun appears in same position relative to fixed stars as seen by observer on Earth; 365 ¼ solar days

question

New Moon

answer

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

question

Full Moon

answer

• 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

question

First Quarter (Waxing Moon)

answer

• rises at noon and sets at midnight

question

Third Quarter (Waning Moon)

answer

• rises at midnight and sets at noon

question

Sidereal Month

answer

• period of Moon's revolution around Earth • 27 1/3 days

question

Synodic Month

answer

• 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

question

LUNAR DAY

answer

• 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)

question

LUNAR ORBIT

answer

• 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

question

ECLIPSES

answer

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)

question

umbra

answer

dark shadow see Total Eclipse

question

penumbra

answer

shadow not as dark (because some light bent in Earth's atmosphere

question

LUNAR ECLIPSE

answer

• 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)

question

• Total Lunar Eclipse

answer

whole of Moon moves through umbra

question

• Partial Lunar Eclipse

answer

part of Moon moves through umbra

question

Penumbra Lunar Eclipse =

answer

Moon moves through penumbra only

question

SOLAR ECLIPSE

answer

• 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

question

Path of Totality

answer

• 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

question

EARTH-MOON SYSTEM

answer

• 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

question

PLANETS

answer

• 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)

question

OBSERVING STARS

answer

• 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

question

Ecliptic

answer

Sun (and planets) moves along ecliptic from point of view of observer on Earth

question

Zodiac

answer

Constellations along Ecliptic

question

Constellation

answer

group of stars near each other on sky as seen by observer on Earth - may or may not be near each other in space

question

PRE-HISTORY ASTRONOMY

answer

• 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)?

question

EVIDENCE?

answer

• 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

question

Aristarchus (~260BC)

answer

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

question

Hipparchus

answer

- early star catalog

question

Planetary Motion

answer

most Greek models had planets orbitting Earth (Aristotle (geocentric world view) and Plato (perfect motion is circular))

question

Ptolemaic Model (100AD)

answer

geocentric planetary orbits + epicycles to explain planet retrograde motion

question

Nicholas Copernicus (1473 - 1543 AD)

answer

• 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

question

Tycho Brache (1546 - 1601 AD)

answer

• 30 years of systematic naked-eye observations of planets, moons, stars

question

Johannes Kepler (1571 - 1630 AD)

answer

• mathematically analyzed Tycho Brache's data Kepler's Laws of Planetary Motion

question

KEPLER'S FIRST LAW

answer

The orbit of each planet is an ellipse with the Sun at one focus

question

Perihelion

answer

closest point in orbit to Sun

question

Aphelion

answer

farthest point in orbit from Sun

question

KEPLER'S SECOND LAW

answer

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

question

KEPLER'S THIRD LAW

answer

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'

question

GALILEO

answer

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

question

Acceleration

answer

= 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

question

Momentum

answer

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

question

Force

answer

mass x acceleration

question

Mass

answer

is amount of matter ('weight' is force of gravity acting on mass on weighing scales)

question

Four Fundamental Forces of Nature

answer

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

question

Other Macroscopic Forces

answer

friction, drag, push, pull

question

FIRST LAW

answer

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

question

SECOND LAW:

answer

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

question

THIRD LAW:

answer

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

question

Angular Momentum = m r v

answer

where r is distance from focus of orbit to body of mass m and velocity v

question

Torque = r F

answer

if force F is perpendicular to r

question

Torque = 0

answer

if force F is parallel to r

question

Conservation of Angular Momentum:

answer

angular momentum is conserved if net torque on body is zero

question

m r v = constant for a given planet in its orbit

answer

(because the force of gravity is always perpendicular to planet's velocity and so torque is zero)

question

when r is small, v is large

answer

(ie planet moves faster when closer to Sun)

question

when r is large, v is smal

answer

l (ie planet moves slower when further from Sun)

question

Conservation of Energy

answer

can't create or destroy energy, can only change from one form to another

question

kinetic energy

answer

energy of motion E = ½ mv2

question

radiative energy

answer

E µ f µ 1/λ (where f is frequency, λ is wavelength of light)

question

mass energy

answer

E = mc2

question

potential energy

answer

(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)

question

Thermal Energy

answer

kinetic energy of many particles eg gas particles

question

Temperature

answer

average kinetic energy per particle

question

FORCE OF GRAVITY

answer

• 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

question

Gravitational Potential Energy

answer

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

question

• Kepler 1:

answer

Newton mathematically showed bound orbits (of planets, moons, satellites) are ellipses and unbound orbits are parabolae and hyperbolae

question

Kepler 2:

answer

conservation of angular momentum

question

Kepler 3

answer

P2 µ A3 from equations (observe orbits and use to determine mass of binary stars etc)

question

Free‐Falling

answer

= 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)

question

Total Orbital Energy = Kinetic Energy + Gravitational Potential Energy

answer

• 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)

question

ESCAPE VELOCITY

answer

minimum launch velocity an object must have to reach an infinite distance from the planet (ie to escape to Deep Space)

question

Low Earth Orbit (LEO)

answer

• 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)

question

Medium Earth Orbit (MEO or ICO)

answer

• 2,000 ‐ 36,000 km above Earth's surface • speed 11,000 ‐ 27,000 km/h • orbital period 2 - 24 hours • eg GPS

question

Geostationary Orbit (GEO)

answer

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

question

Geosynchronous Orbit

answer

• orbital period = 24 hours • 36,000 km above Earth's surface • if orbit is tilted satellite will not be geostationary

question

Launch

answer

• 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

question

TIDES

answer

tides and tidal stress are due to the difference in gravity felt at two different locations

question

Moon

answer

• 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

question

Spring Tide

answer

= high tide increased when Earth + Moon + Sun roughly aligned ‐ occurs twice a month

question

Neap Tide

answer

high tide decreased when Moon at right angles to Sun ‐ occurs twice a month

question

TIDAL FRICTION

answer

• 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

question

Wavelength λ

answer

distance between 2 crests or 2 troughs

question

Frequency f =

answer

= number of crests passing per unit time

question

Speed of Light

answer

constant = 3 x 108 m s-1 = wavelength x frequency

question

• Energy of Light

answer

increases as frequency increases or wavelength decreases

question

ATOM

answer

• 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

question

isotope

answer

same number of p, different number of n

question

radioactive

answer

unstable combination of p+n in nucleus

question

electrons

answer

• 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

question

• continuous spectrum

answer

m (eg thermal emission from warm body)

question

emission lines

answer

at specific wavelengths (bright lines)

question

absorption lines

answer

at specific wavelengths (dark lines in spectrum)

question

THERMAL RADIATON

answer

• emitted by every object with a temperature T greater than 0°K

question

Stefan-Boltzmann Law:

answer

Each square meter of a hotter object radiates more light at all wavelengths than a colder object ( µ T 4 )

question

Wien's Law:

answer

Hotter objects emit light with a higher average energy ie radiation from a hotter object peaks at a shorter wavelength and higher frequency

question

DOPPLER SHIFT

answer

• approaching object's light is 'blueshifted' to shorter wavelength (and higher frequency) • receding object's light is 'redshifted' to longer wavelength (and lower frequency)

question

Light-collecting area:

answer

• 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

question

Angular resolution

answer

= 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

question

Magnification

answer

• goes as diameter of telescope larger telescopes have greater magnification

question

REFRACTING TELESCOPE

answer

• 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

question

REFLECTING TELESCOPE

answer

• uses large curved primary mirror to collect and smaller secondary curved mirror to focus light • largest telescopes today are reflectors

question

INTERFEROMETER

answer

• 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

question

GROUND-BASED TELESCOPES

answer

• ability to observed light is affected by atmospheric turbulence and absorption

question

Best Sites for Submillimeter, Infrared and Visible Telescopes:

answer

• mountain tops, above clouds and water vapor • away from light pollution • good year-round weather

question

Adaptive Optics:

answer

• to cancel out atmospheric distortions which cause stars to 'twinkle'

question

Radio:

answer

• 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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