Astronomy 110 Final

The declination of a star in our sky

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Terms in this set (490)

The angle between the celestial equator and the star, measured along a great circle Passing through both celestial poles.

The angle between your zenith and your horizon is

90°.

The Sun rises due east in the sky when viewed

from any site on the Earth, but ONLY on the first day of spring and the first day of
fall.

Two celestial coordinates, which together describe a star's position precisely in our sky, are:

right ascension and declination

Which of the following lines or points is always directly over your head, no matter where on the Earth you go?

The Zenith

The nightly motion of objects across our sky from horizon to horizon is caused by

the rotation of the Earth on its axis.

As an observer moves toward increasing latitude, the number of circumpolar stars

Increases.

An observer on the equator will be able to see what fraction of the overall sky over a period of one year?

100%

$Image: An observer on the equator will be able to see what fraction of the overall sky over a period of one year?$

Where would you have to be in order to see the north celestial pole directly over your head (i.e., in your zenith)?

At the North Pole of the Earth

Leap years, containing an extra day, are necessary because

the length of a year is not an exact number of days.

The ecliptic can be defined asthe path traced out by the Sun in our sky over one year against the background starsThe ecliptic crosses the celestial equatorat two points, known as equinoxesWhat will the right ascension of the Sun be on June 21 of this year?6 hours 0 minutesIf the Earth's spin axis were to be perpendicular to the plane of its orbit (the ecliptic), seasonal variations on the Earth wouldbe nonexistentFrom the Earth's North Pole, how long will the Sun remain above the horizon once it first appears at the beginning of spring?About 6 monthsWhen the Sun is at one of the equinoxes,day and night are of equal length everywhere on the Earth.At the summer solstice in the northern hemisphere, the Sunreaches its highest angle in the sky for the whole year.Precession isThe slow coning motion of the spin axis of the Earth, similar to that of a spinning top.Why do we see different phases of the Moon?Because the illuminated half of the Moon becomes more or less visible from Earth as the Moon orbits the EarthAt approximately what time will the new Moon rise?Close to sunriseEquinoxThe two days of the year on which neither hemisphere is tilted toward or away from the sunWhen will the first-quarter Moon rise, approximately?NoonWhen does a full Moon rise, approximately?At SunsetWhy is the period between two successive full Moons NOT equal to the Moon's orbital period, or sidereal month?Because the Earth-Moon system is also orbiting the SunA solar eclipse occurs on the Earth whenthe Moon casts a shadow on the Earth.What is the phase of the Moon during a total solar eclipse?NewIn view of the elliptical orbits of the Earth and the Moon, which of the following conditions will result in the longest period of totality during a total solar eclipse?The Earth is farthest from the Sun when the Moon is closest to the Earth.EquatorAn imaginary circle around the middle of the earth, halfway between the North Pole and the South PolePrime MeridianAn imaginary line passing through the Royal Observatory in Greenwich, England, which marks the 0° line of longitude.Blue LightHot planetRed LightCold planetThe summer triangleThree stars, Deneb, Altair, and VegaSiriusThe brightest starDeclinationA measure of how far north or south an object is from the celestial equatorRight AscensionThe angular distance eastward along the celestial equator from the vernal equinox to the intersection of the hour circle that passes through the bodyTh constellations through which the Sun moves throughou the year as it travels along the ecliptic are calledThe zodiac constellations.sidereal dayTime for 360 degree turn (23 hours, 56 minutes, and 4 secondsUmbraIntense shadowPenumbrapartial shadowIn the geocentric model of the solar system developed by PtolemyThe planets move in circular epicycles while the centers of the epicycles move in circular orbits around the EarthWhen observing planetary motions from the Earth, the phrase "retrograde motion" refers toA slow westward motion of the planet from night to night compared to the background stars.Solar planets abbreviationMVEMJSUNThe Copernican system for planetary motions isSun-centered, with the planets moving in perfect circles around the Sun.When a planet is seen at opposition, it is alwaysat its closest point to the Earth.What is the difference between the synodic and sidereal periods of a planet?The synodic period refers to the planet's period with respect to the Earth's motion, whereas the sidereal period is the true period with respect to the background stars.Kepler's first law states that a planet moves around the Sunin an elliptical orbit, with the Sun at one focus.Kepler's second law states that a planet moves fastest when itis closest to the Sun.Kepler's second law statesA line joining a planet to the Sun sweeps out equal areas in equal times.Kepler's third law can be described in which of the following ways?The larger the orbit, the longer it takes for the planet to complete one revolution.Kepler's third law tells us thatthe square of a planet's period in years is the same number as the cube of its semimajor axis in AU.Galileo's early observations of the sky with his newly made telescope includedthe discovery of the phases of VenusWhich of the following statements CORRECTLY states the significance of Galileo's observation that Jupiter has satellites (moons)?It showed that bodies can orbit an object other than the Earth.According to Newton's first law,if no net force is acting upon an object, then both the object's speed and direction of travel will be constant.The acceleration of an object is defined asthe rate of change of its velocity.Which of the following four objects or persons is NOT accelerating?An Olympic swimmer exerting considerable force to maintain a constant speed in a straight line through the waterTwo spaceships that have different masses but rocket engines of identical force are at rest in space. If they fire their rockets at the same time, which ship will speed up faster?The one with the lower massAn unbalanced force acting on an object will ALWAYS cause it tochange its speed or its direction of travel or both.Which of the following statements is a CORRECT version of Newton's third law? (Action & ReactionWhenever some object A exerts a force on some other object B, B must exert a force of equal magnitude on A in the opposite direction.A person standing on a bathroom scale sees a reading on the scale of 148 pounds. This person is acted on bytwo forces of equal size acting in opposite directions.The force of gravity between two objects is proportional tothe product of their masses.How was the planet Neptune discovered?It was discovered by mathematical prediction using Newton's laws.Which fundamental particle is believed to create the physical property called "mass" when it interacts with other particles?The Higgs Boson particleDeferentrespectfulRetrograde motionthe apparent backward movement of a planetInferior ConjuctionVenus or mercury lies between the earth and sunParallaxthe apparent change in position of an object when seen from different placesTycho Brahe(1546-1601) established himself as Europe's foremost astronomer of his day; detailed observations of new star of 1572.The Higgs BosonThe particle that helps to explain why matter is made of mass is...PerhelionWhen the planet is closest to the sun.AphilionWhen the planet is the farthest from the sun.Newton's first law of Inertiaan object at rest will stay at rest, an object that is moving will stay moving unless disturbed by an un balenced force.Newton's second lawF=massNewton's third lawEvery action has an equal and opposite reactionInferior planetsMercury, Venus are closer to sun than earthSuperior planetsPlanets further from the sun than Earth; Mars, Jupiter, Saturn and Uranus.When Venus at superior conjunction?It is at its greatest distance from the EarthEccentricitiesodd behaviorElectromagnetic radiation, moving through space with the speed of light, consists ofoscillating electric and magnetic fields, always inseparable, always having the same frequency and wavelength, and traveling in the same direction.What is the relationship between color and wavelength for light?Wavelength increases from violet to red.In which of the following parameters does a photon of blue light NOT differ from a photon of yellow light, in a vacuum?SpeedWhat is the one fundamental difference between X rays and radio waves?Their wavelengths are very different.Our present understanding of the nature of light is that itdisplays behavior of both waves and particlesVisible light occupies what position in the whole electromagnetic spectrum?Between infrared and ultravioletWhich of the following wave effects is NOT electromagnetic in nature?Seismic wavesThe two ranges of electromagnetic radiation for which the Earth's atmosphere is reasonably transparent arevisible and radio radiationThe main reason for building large optical telescopes on the Earth's surface isto collect more light from faint objects.What is refraction of light?The change in direction of a light ray as it passes at an angle from one transparent material to another which has a different optical densityA Newtonian telescope usesone curved mirror and one flat mirror at a 45° angle to the first mirror axisA Cassegrain reflecting telescope is constructed using aconcave primary mirror followed by a smaller convex secondary mirror that reflects light back through a hole in the primary mirror.What is the magnification of a Newtonian telescope that has a primary mirror of diameter 0.25 m and focal length of 2 m when used with an eyepiece of focal length 25 mm and an optical diameter of 5 mm?80 timesIn general, doubling the diameter of an optical telescope willquadruple the light-gathering power and double the angular resolution.What is a CCD (charge-coupled device)?An array of small light-sensitive elements that can be used in place of photographic film to obtain and store a pictureHow does the speed of light in a substance such as glass compare to the speed of light in a vacuum?The speed of light in glass is slower than the speed of light in a vacuum.What is the main optical element of a refracting telescope?A lensA refracting telescope has an objective lens of focal length 40 cm and a diameter of 10 cm, and an eyepiece of focal length 5 cm and diameter 1 cm. What is the magnifying power of this telescope?8xWhat is the reason for the fact that a reflecting telescope used at prime focus does NOT suffer from chromatic aberration?All wavelengths of light are reflected by the same amount irrespective of color.Which of the following types of telescopes is most seriously affected by chromatic aberration?A refracting telescopeA spherical mirror suffers from spherical aberration becausedifferent parts of the mirror focus the light at different distances from the mirror.The major cause of blurring and unsharp images of objects observed through very large telescopes, at the extreme limit of magnification, isair turbulence in the Earth's atmosphere.The best Earth-based sites for modern large astronomical telescopes, which provide the least seeing effects upon astronomical images, areon the tops of high mountains, above a large fraction of the disturbing atmosphereWhy was adaptive optics developed?To compensate for image distortion caused by the Earth's atmosphereHow does angular resolution for a given diameter of telescope depend on wavelength?Angular resolution worsens as wavelength increases.The main reason that the angular resolution of a 20-m diameter radio telescope is worse than that of a 0.5-m diameter optical telescope is thatangular resolution gets worse as wavelength increasesHow is interferometry used in radio astronomy?Signals from two or more different radio telescopes are combined to produce a single image of greater angular resolution than from any one telescope alone.Telescopes are placed in space to view distant galaxies primarilyto avoid the absorption and distortion of the light or other radiations within the atmosphere of the Earth.Parabolathe graph of a quadratic functionHyperbolaThe set of all points in the plane such that the absolute value of the difference of the distances from two given points in the plane, called foci, is constant.The change in direction as light travels from one medium into another is calledRefractionthe resulting spread of colorscalled a spectrum (plural, spectra).Christiaan HuygensSaid light is a wave and it does not change directions when intersecting with another beam of lightThe constant speed of light in a vacuumHas been measured to be 299,792.458 km/sEinstein proposed that light travels aswaves enclosed in discrete packets, now called photonsthe shorter the wavelengththe higher a photon's energyA megahertz isa million hertz or a million cycles per secondIn experiments with electric sparks in 1888, Hert succeeded in producingelectromagnetic radiation few centimeters in wavelength, now known as radi waves.Nanometerone billionth of a meterInfrared radiationElectromagnetic waves with wavelengths that are longer than visible light but shorter than microwaves.The doppler effectas a wave source approaches, an observer encounters waves with a higher frequency. As the wave source moves away, an observer encounters waves with a lower frequency.TWO BASIC TYPES OF TELESCOPES1.Reflecting Telescopes use a mirror to gather and collect light. 2.Refracting Telescopes use a lens to gather and collect light.The Kelvin scale measurestemperature in Celsius-sized degrees above absolute zero which is -273cTo a physicist, a blackbody is defined as an object thatabsorbs all radiation that falls upon it.The star Vega has a higher surface temperature than the Sun. If so, then, with IR referring to infrared and UV referring to ultraviolet,Vega emits more IR and more UV flux than the Sun.Wien's law, relating the peak wavelength (Lamada) max of light emitted by a dense object to its temperature T, can be represented byLamada max T = ConstantWhy does the Sun look red when it is setting?The Earth's atmosphere scatters shorter wavelength light more easily than longer, so more red light is left to reach our eyes.A spectrograph is a scientific instrument thatspreads out light from a source into its component colors or spectrum.The dark absorption lines in the solar spectrum are causedby a cooler layer of gas overlying the hot solar surface, which contains many elements, including hydrogen, helium, magnesium, calcium, iron, etc.An atom consists ofnegatively charged electrons moving around a very small but massive, positively charged nucleus.The position of an element in the periodic table, its atomic number, is equal tothe number of protons in the nucleus of the atom.Two different isotopes of the element selenium will havethe same number of protons but a different number of neutronsO III isdoubly ionized oxygen (an oxygen atom that has lost two electrons).The majority of the mass of ordinary matter resides inthe nuclei of atomsIn Bohr's model of the hydrogen atom, light is emitted wheneveran electron jumps from an upper to a lower energy level or orbit.The Balmer series of visible spectral emissions from hydrogen gas arises from transitions in which electrons jump between energy levelsfrom higher levels to the first excited level, n = 2.The observed change in wavelength of light due to the Doppler effect occursONLY when the light source has a radial velocity (i.e., motion toward or away from the observer).Proper motion isthe motion of a star or other object across (at right angles to) the line of sight.The radial velocity of a star or other object is measured byobserving the Doppler shift of spectral lines in the light from the object.A "red-hot" objectis the coolest of all glowing bodies.When it is hot enough, like a fire or the Sun, λmax is in the range ofvisible light, giving a hot object its characteristic color.AtomsMICROSCOPIC COMPONENTS MADE UP OF PARTICLES ELECTRONS, PROTONS AND NEUTRONS.ELECTRONSNegatively charged subatomic particlesPROTONSIn the nucleus of an atom, positively chargedNEUTRONSthe particles of the nucleus that have no chargeBLACKBODY RADIATIONthe radiation emitted by a blackbody, which is a perfect radiator and absorber and emits radiation based only on its temperatureAs the object heats up, itgets brighter, emitting more photons of all colors (wavelengths).WHEN FIRST HEATED THE POKER GLOWSDIMMLY AND IS REDAS THE TEMPERATURE RISES, THE POKERBECOMES BRIGHTER AND GLOWS ORANGEAT HIGHER TEMPERATURES THE POKER BECOMESEVEN BRIGHTER AND GLOWS YELLOWStars, molten rock, and iron bars are approximations of an important class of objects that scientists callblackbodiesThe bigger an object is,the brighter it is at all wavelengths.Wein's Displacement Lawhotter objects radiate at shorter wavelengthsContinuous spectrumblackbody emits light at all wavelengthsAbsorption lines spectrumatoms in gas cloud absorb light of certain wavelengths, producing dark lines in the spectrumEmission line spectrumatoms in gas cloud reemit absorbed light energy at the same wavelengths at which they absorbed it)SeleniumSe 34 Atomic mass: 78.96NUCLEUSTINY AND MASSIVE CENTER CONTAINING PROTONS AND NEUTRONSTHE ELECTRON CLOUDEXTENDS FAR FROM THE NUCLEUSVega ismoving toward us (blueshift) with a speed of 14km/s (determined from the amount of the shift).The major constituents of the Earth's atmosphere are77% nitrogen and 21% oxygenBillions of years ago, the Earth's atmosphere was composed primarily of carbon dioxide. What happened to much of this carbon dioxide?It was dissolved into the Earth's oceans.The presence of oxygen in the Earth's atmosphere is thought to result directly from what type of process?Biological activity of plants and animalsAn "ozone hole" isa region of the stratosphere above the South Pole where ozone levels occasionally drop to very low levels.What is the most important reason why we need the ozone layer above us?It shields us from harmful solar ultraviolet radiation.In which layer of the Earth's atmosphere does all of the weather occur?The troposphereHow was the Mid-Atlantic Ridge formed?Molten rock pushed up from the Earth's interior and forced two crustal plates apartWhat is the cause of the great mountain ranges on the Earth, such as the Rockies, the Andes, and the Himalayas?A collision of two tectonic plates that are moving at different velocities across the face of the EarthOn the Earth, the majority of earthquakes occuralong the boundaries of major tectonic plates.The motions of large portions of the Earth's surface, the "plates," are caused byconvective flow of material in the Earth's interior.The Earth's mantle, the semi-molten layer below the crust, is composed largely of what chemical materials?Minerals rich in iron and magnesiumWhat is believed to be the composition of the Earth's core?Essentially pure ironWhat is the relationship between the mantle and the crust of the Earth?New crust is formed by magma rising from the mantle in some places, and old crust is pushed back down into the mantle in other places.The magnetic field of the Earth is caused byelectric currents flowing in the molten core.What causes the phenomenon of the aurora?Charged particles from the magnetosphere strike atoms in the upper atmosphere, causing them to emit characteristic colors of light.What is the diameter of the Moon compared to that of the Earth?About 1/4 of the diameter of the EarthMost of the craters on the Moon were formed bybombardment by interplanetary meteoritic materialMaria areancient lava flood-plains.What is the name of a long, winding crack in a lunar mare?A rilleMost of the mountain ranges on the Moon arethe circular edges and rims of large maria that have been formed by impacts from large objects.A regolith isa layer of pulverized rock on the surface of a planet or other object.Water has recently been discovered on the Moon in the form ofice in deep craters near the north pole, perpetually shaded from sunlight.Which of the following theories is now considered to be the most likely for the formation of our Moon?Collision-ejection theory, where an interplanetary collision knocked material into orbit around the Earth that eventually formed into the present-day MoonHow many "tidal bulges" are there on the Earth caused by the Moon's gravity?Two, one facing (almost) directly toward the Moon and one (almost) directly away from the MoonWhich of the following describes the dynamics of the Earth-Moon system?The Earth's rotation is slowing down, whereas the Moon is moving slowly outward away from the Earth.The first earth's sphereTroposphereThe second Earth's sphereStratosphereThe third Earth's sphereMesosphereThe fourth Earth's Sphere and finalIonosphereAt one point, the continents are believed to have been together, in the form of a supercontinent calledPangaea.Why is it relatively difficult to observe details on the surface of Mercury from the Earth?Because it is a small object that always appears close to the Sun in our skyWhich of the following statements about the similarities of Mercury and our Moon is NOT true?They both have large, circular, and relatively flat basins or maria on parts of their surfacesMercury, unlike the Moon, has extensive plains between the craters. The reason for this is thought to be thatthe plains on Mercury are older than the maria on the Moon. Thus, more time has elapsed during which cratering has erased evidence of earlier maria on MercuryHow do we know the Caloris Basin on Mercury was formed late in the period of intense bombardment?The basin contains very few craters.The impact that formed the Caloris Basin on Mercury also created intense seismic waves that disrupted the surface of Mercury on the opposite side of the planet. Which other solar system feature is known to have involved a major impact with a similar result?Mare Orientalis on the MoonMercury is unique among the inner planets in havingan iron core that occupies almost half its volume.Both Mercury and the Earth have global magnetic fields. Compared to the Earth, which feature is Mercury known to lack that is thought necessary for generating such a field?Rapid planetary rotationWhy has Mercury become locked into a 3-to-2 spin orbit coupling, instead of a 1-to-1 coupling like the Moon around the Earth?Mercury's orbit is very eccentric, so its orbital speed varies while its rotation rate remains constant, and this prevents a 1-to-1 lock.Mercury's atmosphere isalmost non-existentThe conditions on the surface of Venus area high pressure, high temperature, carbon dioxide atmosphere.The clouds in the atmosphere of Venus consist primarily ofdroplets of sulfuric acidThe main reason for the very high temperature (750 K) on the surface of the planet Venus is thought to bethe absorption of visible radiation by the Venusian surface and the subsequent trapping of infrared radiation emitted by the surface by the atmosphere and clouds.The overall geography of the Venus surface has been determined largely byradar techniques from orbiting spacecraftThe most common surface features on Venus arevolcanoes and lava flows.Venus rotatesin the opposite direction as the Earth, but very slowly.Mars has a period and direction of rotation that area little longer than 24 hours and in the same direction as the Earth.What is the principal reason we have no volcanoes on the Earth anywhere near the size of Olympus Mons?Because of tectonic activity on the Earth, a volcano does not sit over the same spot for long periods and continue to grow.Hot-spot volcanism is a process thatproduces gigantic volcanoes on Venus and Mars but chains of smaller volcanoes on the Earth (e.g., the Hawaiian Islands).What are the Valles Marineris?A large rift valley system associated with the great volcanoes on MarsThe reddish color of Mars is probably due tothe glow from the very high temperature surface on the sunlit parts of Mars.Mars experiences similar seasonal changes to those on the Earth becauseits spin axis is tilted at about the same angle to its orbital plane as is the Earth's axisAtmospheric pressure at the surface of Mars, compared to the atmospheric pressure at the Earth's surface, isless than 1/100.the polar caps on Mars are most likely made up ofwater and carbon dioxide icesTomorrow's (and most day's) weather forecast for Mars is likely to besunny, possible thin, high clouds, windy.The moons of Mars areirregularly shaped, cratered, and groovedThe pressures of the atmospheres at the surfaces of Mercury, Venus, and Mars, in terms of the pressure at the surface of the Earth (known as 1 atmosphere), are0; almost 100 atmospheres; 1/100 atmosphereWhich of the following are the youngest?The oldest craters on VenusMercury also hasnumerous long cliffs, called scarps, believed to have formed when the planet cooledMercury's iron coretakes up a much larger percentage its volume than that of Earth.ProgradeThe counterclockwise spin of a planet or moon as seen from above the planet's North Pole.calderaa large volcanic craterdust devilA tornado in the desert that stretches from ground to cloudnorthern vastnessRelatively young, crater free terrain in the Northern hemisphere of MarsScarpcliff on Mercury; similar to those on Earth but much higher.southern highlandsHeavily cratered (Mars)The two moons of Mars,Deimos and Phobos, are small and non-spherical in shape. These are planetesimals captured by Mars.The extreme heating of Venus' surface is caused bythe greenhouse effectWhat is the mass of Jupiter compared to other objects in the solar system?Twice the mass of all other planets combinedWhat characteristic features are seen on the visible surface of Jupiter?Light and dark bands parallel to the equatorWhat are the light-colored bands on Jupiter called?ZonesWhat is the Great Red Spot on Jupiter?A large, long-lived, anticyclonic storm that is maintained by the differential rotation of Jupiter's atmosphereWhich feature of Jupiter leads to the confinement of its clouds in very narrow bands around the planet?Its rapid rotationThe composition of the clouds that we see on Jupiter issimilar to those of the Earth (water droplets and crystals of frozen water) in the lower levels, but very different (e.g., ammonia crystals and other chemicals) in the higher levels.Which of the following chemicals is the most abundant in the outer atmosphere of Jupiter?NH3 (ammonia)The predominant large-scale atmospheric circulation pattern on Jupiter is characterized bystrong winds blowing parallel to the equator, but in opposite directions at different latitudes.The low average density of Jupiter (about 1300 kg/m3 compared with that of water, 1000 kg/m3) indicates that this planet is composed mainly ofhydrogen, in liquid or gaseous form.What is the source of Jupiter's intense magnetic field?Electric currents in Jupiter's liquid hydrogen layerHow does the magnetosphere of Jupiter compare to that of the Earth?It is much larger because of Jupiter's large magnetic field and the weakness of the solar wind at Jupiter's orbital distance from the Sun.How many moons are now known to orbit Jupiter?At least 67 moonsHow many moons of Jupiter were seen by Galileo?4, with his new telescopeThe overall interior structure of the Jovian planets is expected to befour-layered: a rocky core, a semi-fluid ice layer, a liquid mantle of hydrogen, and a gaseous hydrogen and helium atmosphere.Which is the largest planetary satellite in the solar system?Jupiter's satellite Ganymede"Markings" on the surface of Saturn aresimilar in appearance to those on Jupiter, but much less distinct.The physical structure of Saturn's rings isa sequence of many thousand separate ringlets consisting of ice blocks and ice-coated rock.Saturn's moon Titan is different from all other moons of the planets becauseit possesses a thick atmosphere.What is the appearance of Saturn's satellite Titan when viewed from space?Its surface is not visible under a featureless cloud cover.The major constituent of the atmosphere of Titan (the largest moon of Saturn) isnitrogen, N2.What is the visual appearance of Uranus from space?Blue-green and featurelessBy what angle is the rotation axis of Uranus tilted from the vertical to its orbit?98°Which planets rotate about their axes in a retrograde direction?Venus, Uranus, and PlutoWhat is believed to be the basic structure of the interior of Uranus?A rocky core, a thick layer of highly compressed liquid water, a thick outer layer of liquid hydrogen, and a thin gaseous atmosphereHow were the rings of Uranus discovered?From the Earth, when each ring momentarily blocked the light from a background starMiranda, a satellite of Uranus,appears to have been reassembled from separate parts after being shattered by an impact.How was Neptune discovered?By a careful application of Newton's laws to the somewhat irregular motions of UranusWhat is the visual appearance of Neptune from space?Blue-green with white, high-altitude clouds and dark stormsNeptune's predominantly blue appearance is caused byabsorption of the red end of the spectrum of reflected sunlight by the methane in its atmosphere.Which ONE of the following four statements applies to ALL FOUR of the Jovian planets?They are thought to have substantial rocky coresWhich planets are believed to have a thick layer of water mixed with ammonia and methane in their interiors?Uranus and NeptuneThe electrically charged particles that produce electric currents and therefore magnetic fields when they move inside Uranus and Neptune aremolecules such as ammonia (NH3), which become ionized when in solution in water.What is the typical thickness of Saturn's rings?2 kmTriton, the largest satellite of Neptune, hasa surface of ice with frozen lakes, plumes of escaping gas, and few craters.The effect of tidal forces caused by Triton on Neptune as it moves in its retrograde orbit will lead to Tritonspiraling in toward Neptune to eventual destruction by differential tidal forces on the moon.How was the planet Pluto discovered?By searching photographs of the sky for an object that moved against the background of distant starsWhat is the moon of the planet Pluto called?CharonWhat is unique about the Pluto-Charon system, compared to all other planets in the solar system?Both Pluto and Charon are in synchronous rotation, so each object maintains the same face toward the other object at all times.What is the probable composition of both Pluto and its satellite, Charon, based on their average densities?About half rock and half iceIo,the closest moon to Jupiter, is covered with many active volcanoes.Ganymede,the largest satellite in the solar system, is even larger than Mercury.Roche limitthe closest distance from the center of a planet that a satellite can approach without being pulledshepherd moonA moon that orbits right on the inside of a ring and thus contorts its shapeThe asteroid belt exists between the orbits of the planetsMars and JupiterIf all the material in the asteroid belt were to be combined to produce a planet, how big would it be?About 1500 km in diameter, significantly smaller than the MoonThe number of asteroids with diameters greater than 100 km isabout 230.The total number of asteroids orbiting the Sun among the planets is estimated to bemore than a million.How would a typical asteroid appear on a time exposure photograph of the sky as it orbited the Sun if the camera were tracking the background stars.It would produce a short trail as it moved slowly against the background stars.Where do the Trojan asteroids orbit the Sun?In circular orbits at the same orbital distance as JupiterWhat is the difference between an Apollo asteroid and an Amor asteroid?Apollo asteroids cross the orbit of the Earth, whereas Amor asteroids cross the orbit of Mars but not the Earth's orbit.The Kuiper belt isa flat or donut-shaped distribution of distant comets around the Sun, extending out about 50 AU.Most comet nuclei are believed to bepieces of dusty ice left over from the formation of the solar system.Comet tails are the result ofmelting and evaporation of ices from the comet coreA comet's tailalways points away from the Sun, regardless of the motion of the comet.The orbits of comets arerandomly oriented in the solar system and can extend far beyond the orbit of PlutoA meteoroid is the name used to describe a solid particle thatis drifting around in space.A meteor shower results fromthe Earth passing through debris of an old comet.Which are the most common types of meteoroids in space?StonesThe most common meteorites to hit the Earth arethe stony meteorites.What fraction of the material arriving on the Earth from outer space is in the form of iron meteorites?B) A few %What fraction of the material arriving on the Earth from outer space is in the form of stony meteorites?95%Stony-iron meteorites are believed tooriginate from differentiated asteroids (in which iron sank to the center).Why are carbonaceous chondrites thought to be original material that formed in the early solar nebula?Their minerals contain up to 20% water, which would have evaporated away if the chondrite had been strongly heated.What is the likely connection between the metal iridium and the demise of the Earth's dinosaur population?Iridium is found in meteorites but is rare on the Earth. The existence of a world-wide layer of it suggests a large meteor impact during the dinosaur age. This probably raised enough dust to block out sunlight and kill the dinosaurs.The approximate temperature of the visible surface of the Sun is5800 K.Granulation on the surface of the Sun is caused byconvective currents carrying heat from beneath the surface.What is the reason why the edge of the Sun's visible disk is darker than the center?We see into shallower layers of the Sun near the edge; the gas is cooler there and so emits less light.What are the names of the three layers in the Sun's atmosphere, in order from lowest to highest?Photosphere, chromosphere, coronaWhat is the solar wind?Material from the corona, accelerated out into spaceSunspots arecooler, darker regions on the Sun's surface.How can we characterize the rotation of the Sun?Differential rotation, with the equator rotating faster than the polesThe sunspot cycle on the Sun isan irregular build-up and decay in the number of sunspots averaging about 11 years, which occasionally fails for a time when no spots appear.Why are sunspots cooler than the rest of the Sun's surface?Sunspots mark the places where the magnetic field lines penetrate the Sun's photosphere. The hot solar plasma beneath is repelled from these field lines and thus inhibit the flow of heat to the surface at these points.An arching column of gas suspended over a sunspot group is called aprominence.Where on the Sun do solar flares occur?Only within sunspot groupsThe solar wind isa gentle outflow of solar material, mostly protons and electrons, that is always moving outward from the Sun.What is the energy source for the Sun?Thermonuclear fusion in the coreFrom which fusion reaction does the Sun derive its power?4H to HeHow much longer can the Sun continue to generate energy by nuclear reactions in its core?About 5 billion yearsTo what do the words "hydrostatic equilibrium" in the Sun refer?The balance of gravity inward and gas pressure outwardThe order of the layers or parts of the Sun, as radius increases, isradiative zone, convection zone, photosphere, chromosphere, and corona.Before 1998, what results were obtained in the detection of solar neutrinos?Only about 1/3 of the expected number of neutrinos were observed, compared to theoretical models of the Sun.Recent solar neutrino experiments have confirmed the suspicion that the explanation for the apparent shortfall in neutrino detection rates over the last 30 years was because2/3 of the solar neutrinos had transformed into types of neutrinos that were undetectable by old detection techniques.The corona of the Sun has a temperature that isabout 1 to 2 million K.Stellar parallax isthe apparent shift seen in the position of a nearby star against more distant stars as we orbit the Sun.Parallax of a nearby star is used to estimate itsdistance from the EarthHow far out into space can we determine stellar distances using telescopes on the Earth if we can only measure stellar parallax values as small as 0.01 arcsec?100 pcApparent magnitude is a measure ofthe brightness of a star, as seen from the Earth.Absolute magnitude is defined as the apparent magnitude that a star would have ifIt were located at exactly 10 pc from the Earth.What is a star's luminosity?The total energy emitted by the star into all space per second, measured in wattsWhy are Balmer absorption lines very weak in the spectra of stars with low surface temperatures, significantly below 10,000 K, for example?Because atoms need electrons that have been excited by high-temperature collisions to the n = 2 level in order to undergo Balmer absorptionSpectral types of stars (e.g., O, B, A, F, G, K, and M) define uniquely theirsurface temperaturesWhich of the following sequences of stellar spectral classifications is in correct order of increasing temperature?M, K, G, F, A, B, OThe symbol He II refers to ahelium atom that has lost one electron.How many electrons are missing from the ionized silicon atom Si IV?ThreeWhat are the two physical parameters of stars that are plotted in the Hertzsprung-Russell diagram?Luminosity and surface temperatureWhat fraction of the stars surrounding the Sun are main-sequence stars?Almost all of them, about 90%What is the physical reason why astronomers can find the luminosity class (I, II, III, IV, or V) of a star using the star's spectrum?The absorption lines in the spectrum are affected by the density and pressure of the star's atmosphereWhich of the following spectral-luminosity classes corresponds to a red supergiant?M2 IWhat is spectroscopic parallax?The distance to a star measured using the spectral-luminosity class of the star and the inverse square lawHow do astronomers measure the masses of stars?By observing the motion of two stars in a binary star systemTo determine the sum of the masses of a visual binary star system, we need to measurethe period and the semi-major axis.The relationship between mass and luminosity of stars on the main sequence is thatthe larger the stellar mass, the larger the luminosity.The radial-velocity curve of a star in a binary star system is a plot against time ofthe variation of Doppler shift of its spectral lines and hence of its speed toward or away from us.An eclipsing binary system consists oftwo stars that periodically eclipse each other, as seen from the Earth.What is a parsec3.26 light-years/ parallax of one arcsecondThe closer the star is to us,the greater the parallax angleProxima Centauri isabout 40 trillion kilometers (25 trillion miles) away. It takes light about 4 years to reach the Earth from there.How luminous is the Sun compared with other stars?The most luminous stars are about a million times brighter and the least luminous stars are about a hundred thousand times dimmer than the Sun.What colors are stars?Stars are found in a wide range of colors, from red through violet, as well as white.Interstellar extinction isthe reduction of the apparent brightness of stars by scattering and absorption of their light by intervening interstellar clouds.What are the two most abundant elements in the universe?Hydrogen and heliumHow is gas distributed in interstellar space?In clumps, concentrated in interstellar cloudsWhat is the characteristic color of a reflection nebula?BlueA reflection nebula is made visible byblue light preferentially scattered by dust grains.Which of the following is true about open clusters?The motions of individual stars are such that all open clusters will eventually disperse.New stars are formed fromhuge, cool dust and gas clouds.What is the typical temperature inside the dense core of a giant molecular cloud that is collapsing to form a star?10 KThe characteristics of an open cluster of stars area few hundred members, often very young and still embedded in the gas and dust from which they were formed.Protostars arevery young objects still contracting before becoming true stars.What is the most important process causing a protostar to stop accreting mass?Radiation and particles from the hot protostar push infalling matter away from the protostar.The "evolutionary track" of a star representschanges in its luminosity and temperature on a graph of these two parameters as the star ages.A brown dwarf isan object intermediate between a planet and a star, with not enough mass to begin nuclear reactions in its core.What is believed to prevent stars from having masses greater than a few hundred solar masses?The temperature becomes so high that the excess mass is pushed back into space by radiation from the star.If we plotted the stars in a YOUNG star cluster on a Hertzsprung-Russell diagram, we would expect to seethe more massive stars on the main sequence and the less massive stars above the main sequence.The definition of a main-sequence star is onein which nuclear fusion reactions generate sufficient energy to oppose further condensation of the star.The "zero-age main sequence" describes the sequence of stars in the Hertzsprung-Russell diagramthat have just reached the main sequence.The total time that the Sun will spend as a main-sequence star isabout 10 billion years (10,000,000,000).The stars that last longest arethose with the smallest mass.Why does the core of the Sun contain more helium and less hydrogen than the surface of the Sun?Thermonuclear reactions have converted much of the original hydrogen in the core into helium.The next stage in a star's life after the main-sequence phase isthe red-giant phase.What makes a red giant star so large?The hydrogen-burning shell is heating the envelope and making it expand.How large will the Sun be as a red giant?About 1 AU radius (out to the Earth's orbit)What happens to the helium-rich core of a star after the core runs out of hydrogen?It contracts and heats up.When is electron degeneracy pressure important in a star?Just before the start of helium burning in the coreThe study of stars in clusters has especially helped astronomers to understandstellar evolution, the development of stars with timeThe characteristic of a globular cluster of stars ishundreds of thousands of members, all very old and generally metal-poor.Which of the following stars are metal-rich?Population I starsWhat is the "turnoff" point for a star cluster?The point in the Hertzsprung-Russell diagram occupied by the highest-mass main-sequence stars in the clusterWhat is a Cepheid variable star?A high-mass star that pulsates regularly in brightnessWhat characteristic of Cepheid variables makes them extremely useful to astronomers?Their absolute magnitude is related directly to their period of pulsation.Nuclear fusion reactions of helium produce primarilycarbon and oxygen nuclei.In a star's evolutionary life, the asymptotic giant branch (AGB) is thehelium shell fusion phase.In the process of helium shell fusion in low-mass stars near the end of their lives, the star moves upward and to the right on the asymptotic giant branch of the Hertzsprung-Russell diagram. In this process, the star isexpanding, cooling, and becoming more luminous.A planetary nebula isa gas shell, the atmosphere of a red giant star, slowly expanding away from the core of the star.In what manner does an isolated white dwarf generate energy?An isolated white dwarf does not generate energy.The characteristics of interiors of white dwarf stars aremainly carbon and oxygen nuclei supported by electron-degeneracy pressure in a volume about the size of the Earth.White dwarf stars are supported from gravitational collapse bydegenerate-electron pressure.There is a mass limit for a star in the white-dwarf phase, the Chandrasakhar limit, beyond which the electron-degeneracy pressure can no longer support the star against its own gravity. This mass limit is1.4 solar masses.The mechanism that gives rise to the phenomenon of the nova ismatter from a companion star falling onto a white dwarf in a close binary system, eventually causing a nuclear explosion on the dwarf's surface.Each successive stage of core nuclear reactions in a massive star lasts for considerably less time than the previous stage (e.g., for a 25-solar-mass star, carbon fusion lasts for 600 years, while neon fusion lasts for only 1 year). One reason for this is thatthe more massive the nuclei, the fewer there are of them to react together.A high-mass star near the end of its life undergoes successive cycles of energy generation within its core in which gravitational collapse increases the temperature to the point where a new nuclear fusion cycle generates sufficient energy to stop the collapse. This process does not work beyond the silicon-fusion cycle that produces iron. Why is this?Fusion of iron nuclei into heavier nuclei requires energy rather than producing excess energy and therefore will not produce the additional gas pressure to halt the collapse.During its life, a massive star creates heavier and heavier elements in its core through thermonuclear fusion, leading up to silicon and iron. What is the fate of the iron that is created?It is torn apart by high-energy photons at the end of the star's life.What is the source of most of the heavy elements on the Earth and in our own bodies?Explosive nucleosynthesis during supernova explosions of massive starsWhat are cosmic rays?Atomic nuclei and other subatomic particles traveling through space at more than 90% of the speed of lightA Type II supernova isthe explosion of a massive star after silicon fusion has produced a core of iron nuclei.Type II supernovae show prominent lines of hydrogen in their spectra, whereas hydrogen lines are absent in spectra of Type Ia supernovae. Why is this? (Hint: Think about the type of star that gives rise to each of the two types of supernova.)Massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen.What is a pulsar?A rapidly rotating neutron star, producing beams of radio energy and occasionally of X rays and visible lightWhat prevents a neutron star from collapsing and becoming a black hole?Gravity in the neutron star is balanced by an outward force due to neutron degeneracy.The Oppenheimer-Volkov limit to the amount of mass in a neutron star before neutron degeneracy pressure is unable to withstand the force of gravity and the neutron star is crushed out of existence into a black hole isabout 3 solar masses.A black hole is so named becauseno light can escape from it due to its powerful gravitational field.As time progresses, the pulse rate for most solitary pulsars isslowing down since rotational energy is being used to generate the pulses.The source of the beams of electromagnetic radiation (including light in some cases) emitted by pulsars ischarged particles traveling along the magnetic axes of rotating neutron stars; the particles emit light as they are accelerated.How must an object be moving for us to be able to use the theory of special relativity to describe the object?It must be moving at a constant speed in a straight line; how fast it is moving is not importantTwo spaceships are traveling past the Earth at 90% of the speed of light, in opposite directions (i.e., they are approaching each other). One turns on a searchlight, which is seen by scientists aboard the other. What speed do the scientists measure for this light (c = speed of light in a vacuumCSuppose you are in a spaceship traveling toward the Earth at 95% of the speed of light. Compared to when your ship was at rest on Mars, what length do you measure for your spaceship?The same as when it was on MarsSuppose you see a spaceship with a clock on it hurtling past you at 80% of the speed of light. As it goes by, the second hand on the ship's clock ticks off five seconds. How much time elapsed on your clock while this was happening?More than five secondsWhich statement best describes the "fabric" of space and time as outlined by the classical physics of Newton?Space is perfectly uniform, filling everywhere like a fixed network, while time passes at a uniform rate for all observersHow does a gravitational field affect the passage of time?Clocks in a gravitational field run slower than clocks farther from the center of the field when viewed by an observer who is also farther from the center of the field.According to general relativity, why does the Earth orbit the Sun?Space around the Sun is curved, and the Earth follows a geodesic in this curved space.Which of the following is the lower limit for a main-sequence star that will eventually form a black hole?25 solar massesA black hole can be thought of asa region with such a large mass density that even electromagnetic radiation cannot escape.In reference to black holes, a singularity isa place where a nonzero mass occupies zero volume.What is the event horizon of a black hole?The "surface" from inside of which nothing can escapeWhat is the Schwarzschild radius of a black hole?The distance from its singularity to the point where nothing can escape from the black holeWhat is a Schwarzschild black hole?Any non rotating black holeWhat name is given to a rotating black hole?A Kerr black holeIn terms of black holes, what is a wormhole?A direct connection from a rotating black hole to another part of spacetimeWhich of the following techniques has been successful in identifying good candidates for a black hole in our Galaxy?The detection of X rays from a binary star undergoing mass exchange, where masses of component stars can be determinedI always thought nothing could escape from a black hole, yet astronomers are locating black hole candidates by the X rays they emit. How can X rays be coming from a black hole?The X rays come from a highly compressed region in an accretion disk outside the event horizon of the black hole.Where would you look for a supermassive black hole?In the center of a galaxyWhat is a primordial black hole?A black hole created during the formation of the universeIf nothing can ever leave a black hole, can the mass of a black hole ever decrease?Yes, if particle-antiparticle pairs are created outside the event horizon out of gravitational energy from the black hole and one particle enters the event horizon while the other escapesWhat important role do Cepheid variables stars have in astronomy?Distance measurements to distant galaxiesWhy are we able to see only a relatively small part of our Galaxy, the Milky Way Galaxy?Distant stars are obscured by dust in interstellar space.The method used by Harlow Shapley in 1917 to estimate the Sun's location in our Galaxy was the measurement ofthe locations of globular clusters around the Galaxy.When distances were carefully measured from the Earth to globular clusters above and below the Milky Way plane (where our view of them is not obscured by interstellar dust and gas), their distribution was found to bespherically symmetric about a point in the constellation Sagittarius and concentrated in that direction.Radio waves of 21-cm wavelength originate from which component of the interstellar medium?Cool, neutral atomic hydrogenWhich type of radiation has been most effective in evaluating the spiral arm structure of our Galaxy?21-cm radio emission from electron "spin-flip" transitions in cool hydrogen gasWhat quantum transition occurs inside a hydrogen atom to produce a 21-cm radio photon?An electron in the ground atomic state reverses its direction of spin with respect to that of the proton.When we measure the narrow line emissions of hydrogen at 21-cm radio wavelengths along a particular line of sight through the disk of our Galaxy, we can tell the distances to different hydrogen clouds becauseclouds at different distances have different Doppler shifts because of the rotation of the Galaxy.Which of the following components of the Galaxy best outline the spiral arms of the Galaxy?Young O and B stars, dust, and gasWhen we look out into the plane of the Galaxy, how far can we see?About 10,000 lyThe dimensions of the disk of our Milky Way Galaxy arediameter 100,000 ly; thickness 2000 ly.Where is the solar system located in our Galaxy?In the galactic diskWhat is the significance of the object Sagittarius A* ("Sagittarius A-star") in our Galaxy?It appears to be the actual nucleus of the Galaxy.What type of object has been proposed to explain the tremendous activity detected at the center of our Galaxy?A supermassive black holeWhat evidence now exists for a supermassive black hole at the center of our Galaxy?Very rapid motion of matter close to the nucleus of the Galaxy, requiring a very massive body to hold it in orbitWhich of the following statements correctly describes the rotation of our Galaxy?The disk rotates differentially (objects farther from the center take longer to complete an orbit than objects closer to the center), and the halo objects have random orbits with no net rotation of the halo about the center of the Galaxy.The time for the Sun to orbit the galactic center once in its motion in the Galaxy is230 million years.How do we obtain an estimate of the amount of mass that is inside the Sun's orbital path in our Galaxy?By applying Kepler's law to the motion of the Sun and other nearby starsThe present estimate for the total mass of our Galaxy in units of solar mass is about10*12The presence of a very large amount of unseen ("dark") matter in the halo of our Galaxy is deduced fromthe rotation curve of our Galaxy, in which orbital speeds of stars in the outer regions of the Galaxy are significantly higher than is predicted by Kepler's law in which the value for the observed mass in the Galaxy is used.What fraction of the mass of our Galaxy appears to be in the form of dark matter, which we cannot see but can detect through its gravitational influence?About 10%What is microlensing?The focusing of starlight by the gravitational fields of "small" objects like planets or brown dwarfsIn a recent survey of stars in the sky, it was found that occasionally a star that is normally of constant brightness will slowly brighten and then fade back to its original brightness again over the space of several weeks. What is believed to be the cause of this change in brightness?Microlensing by compact objects such as brown dwarfs passing in front of the starWhat physical process has allowed astronomers to measure the overall number and distribution of brown dwarfs in our Galaxy?Their gravitational fields can bend the light from background stars.What has microlensing told us about the role of brown dwarfs in the Galaxy?They cannot be a major component of the dark matter in the Galaxy.In the Hubble classification scheme for spiral galaxies, the tightness of the winding of the spiral arms appears to be related directly tothe size of the central bulge of the galaxy.The typical diameter of a spiral galaxy is about10*5 ly.What mechanism is believed to produce flocculent spiral galaxies?Self-propagating star formation, where star formation occurs in burstsWhat mechanism is believed to produce grand-design spiral galaxies?Density waves in the interstellar mediumWhat is the designation given to a galaxy with a large nuclear bulge and tightly wound arms starting from a bar through the nuclear bulge?SBaHow do most spiral galaxies rotate?The arms trail as the galaxy rotates (arms point backward).What is an elliptical galaxy?A galaxy with an elliptical outline and a smooth distribution of brightness with no structure apparent in the galaxyIn which category of galaxy do we find the largest galaxies in the universe?Elliptical galaxiesWhich of the following types of galaxies contains primarily population II, metal-poor, low-mass, long-lived stars?Elliptical galaxiesAn astronomer studying a cluster of galaxies finds a galaxy that is round and has a disk and central bulge like a spiral galaxy, but has no spiral arms. How should the astronomer classify this galaxy?S0The overall distribution of galaxies through space is now found to havegalaxies concentrated on the surface of huge open spaces or voids, like soap bubbles.A supercluster of galaxies isa cluster of galaxy clusters.What is the Local Group?A cluster of about 40 galaxies of which the Milky Way is a memberWhat is a rich cluster of galaxies?A cluster containing thousands of galaxiesWhat is a poor cluster of galaxies?A cluster containing a few dozen galaxiesA rich, regular cluster of galaxies differs from a rich, irregular cluster in that ithas fewer spirals and more elliptical and S0 galaxies than an irregular cluster.Collisions between galaxiescan and do occur relatively frequently over cosmological times.What is believed to be the origin of starburst galaxies?A recent collision with another galaxy has triggered a wave of star formation.What is believed to be the origin of giant elliptical galaxies?They grew by devouring smaller galaxies.Which one of the following statements is true about clusters of galaxies?The observed visible mass of the galaxies in the cluster is about 10 times too small to hold the cluster together.Many rich, regular clusters of galaxies contain substantial amounts of very hot, intergalactic gas. What is believed to have produced this hot gas?Collisions between galaxies in the clusterThe Hubble law indicates thatthe farther galaxies are receding faster than the nearby galaxies.Which of the following speeds is described by Hubble's law?The speeds of superclusters of galaxies"Standard candles," which are important for finding distances to remote galaxies, arestars and other objects of known intrinsic brightness.What is the brightest "standard candle" found so far, and therefore the one that is visible to the greatest distance?Type Ia supernovaeWhat is the Tully-Fisher relation?The brighter the galaxy, the wider the 21-cm radio emission line.The following distance-measuring techniques, arranged in order of the distance for which they are most effective, from smallest to greatest, arespectroscopic parallax, Cepheid variables, Tully-Fisher relation, and Type Ia supernovae.Why is the universe expanding?because space-time itself is expanding, carrying the galaxies with it.What is the "cosmological redshift"?The stretching of the wavelengths of photons as they travel through expanding spaceIn the expansion of the universe, the expansion takes placeonly over distances about the size of a galaxy or larger; consequently, our Galaxy expands, but the solar system does not.According to Hubble's law, how old is the universe (H0 = Hubble's constant)?Age = H0If Hubble's constant is 75 km/s/Mpc, then the age of the universe is 13 billion years. Suppose it were discovered that Hubble's constant is actually larger than 75 km/s/Mpc. What effect would this have on the calculated age of the universe?It would increase the calculated ageHow does the universe behave, according to the steady-state theory?As the universe expands, new matter is created from which new galaxies form, thus maintaining a "steady state."The cosmic background radiation islow-intensity radio noise, with a 3 K blackbody temperature, almost uniform in intensity in all directionsIn relation to the universe, what does "isotropy" mean?The universe looks the same in all directions.What do superstring theories try to explain?The behavior of matter during the Planck time when all four fundamental forces were unifiedHow many fundamental forces are there in nature at the present time under normal conditions?Four: strong, weak, electromagnetic, and gravitationalWhat are the particles that make up protons and neutrons?QuarksHow do we know that the fundamental forces become unified as the energy of particle interactions increases?Because we have actually seen the start of it in high-energy particle accelerators, where the electromagnetic and weak forces become unifiedWithin which time frame from the initial Big Bang do we believe all four fundamental forces of nature were united into a single force?t = 0 to 10-43 sec, the Planck time, when gravity "froze out" of the universeWhat is the isotropy (or horizon) problem?If the universe expanded at the rate originally predicted, then the parts we see in opposite directions would never have been in equilibrium with each other and should not exhibit the degree of isotropy we observe.If the universe had expanded at its original rate beyond the time when the strong nuclear force became a distinct force (about 10-35 sec after the Big Bang), the isotropy problem would have arisen: Parts of the universe we see in opposite directions would never have been in equilibrium with each other and should not exhibit the degree of isotropy we observe. The proposed solution to this problem iscosmic inflationIn cosmology, what is the "inflationary period"?A short period of extremely rapid expansion when the universe was very youngWhy did the formation of particle-antiparticle pairs (such as protons and antiprotons) from gamma rays come to an end within the first second after start of the Big Bang?The gamma-ray energy, decreased as the universe expandedWhere was most of the helium in the universe created?By nuclear reactions during the first three minutes following the Big BangAt an age of 300,000 years, the temperature of the universe had fallen to 3000 K, and electrons could then combine with protons to produce neutral hydrogen gas. What major transition took place in the universe at this time?It became transparent to light for the first time.Why does the observable universe have an "edge"?Because we cannot see any farther out into space than the distance that light has traveled over the lifetime of the universeDuring the formation of the universe, where did the density enhancements come from that subsequently collapsed to form superclusters of galaxies?From quantum fluctuations in the density of matter during the early Big Bang, which were later expanded by inflationThe very small detected irregularities in the uniformity of the cosmic microwave background are considered to be very important in the study of the evolution of our universe becausethey are thought to have led to the development of the present concentrations of matter and energy in superclusters of galaxies.For how long did continuous star formation last in spiral galaxies?Continuously throughout the galaxy's life, right to the present dayIn which of the following universe scenarios will the present universe evolve to a Big Crunch at some time in the future?A closed universeWhat kind of curvature (geometry of space) does the universe have if the universe is open?HyperbolicWhat kind of curvature (geometry of space) does the universe have if the universe is just on the boundary between being open and being closed?FlatWhat kind of curvature (geometry of space) does the universe have if the universe is closed?SphericalWhich parameter of the present universe, more than any other, is considered to be critical in determining the ultimate fate of the universe?The amount of matter and energy in the universeRecent results from very bright supernovae in very distant galaxies seem to indicate that the expansion of the universeis accelerating (speeding up).What is the difference between dark matter and dark energy?Dark matter is attractive and slows the universal expansion, whereas dark energy is repulsive and accelerates the universal expansion.In a primordial, pre-galactic gas cloud, what is believed to have been the most important condition that caused the cloud to become an elliptical galaxy?The initial rate of star formation was high