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CSET Earth & Space Sciences (219) study materials
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CSET Earth & Space Sciences (219) practice questions

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Question 1Astronomy

Which process powers the Sun's energy output and converts hydrogen into helium in its core?

  1. Nuclear fusion through the proton-proton chain Correct answer.
  2. Gravitational contraction alone
  3. Chemical combustion of hydrogen with oxygen
  4. Nuclear fission of heavy elements

Explanation

The Sun's core fuses hydrogen nuclei into helium, releasing energy through the proton-proton chain, which dominates in stars of the Sun's mass. This fusion requires extreme temperature and pressure to overcome electrostatic repulsion between nuclei.

Question 2Astronomy

The Sun's visible surface, where sunspots appear, is called the:

  1. Convective zone
  2. Chromosphere
  3. Corona
  4. Photosphere Correct answer.

Explanation

The photosphere is the layer from which visible light escapes and where sunspots are observed. It lies beneath the chromosphere and above the convective zone.

Question 3Astronomy

A star's spectral class is most directly determined by which observable property?

  1. Its distance from Earth
  2. Its proper motion
  3. Its surface temperature Correct answer.
  4. Its radial velocity

Explanation

Spectral classes (O, B, A, F, G, K, M) reflect the ionization and absorption-line patterns that depend primarily on surface temperature. Distance, motion, and velocity do not set spectral type.

Question 4Astronomy

Kepler's second law states that a planet sweeps out equal areas in equal times. This implies that a planet moves:

  1. Fastest when farthest from the Sun
  2. Fastest when closest to the Sun Correct answer.
  3. At constant speed throughout its orbit
  4. Slowest when closest to the Sun

Explanation

Equal areas in equal times means the planet covers more arc length when near the Sun, so its orbital speed is greatest at perihelion. This reflects conservation of angular momentum along the orbit.

Question 5Astronomy

Which planet has the most massive ring system in the solar system?

  1. Jupiter
  2. Uranus
  3. Neptune
  4. Saturn Correct answer.

Explanation

Saturn possesses the largest and most massive ring system, composed mainly of water-ice particles. The other giant planets have faint or narrow ring systems by comparison.

Question 6Astronomy

The apparent daily motion of stars across the sky is primarily caused by:

  1. Earth's revolution around the Sun
  2. The precession of Earth's axis
  3. Earth's rotation on its axis Correct answer.
  4. The proper motion of stars

Explanation

Earth's rotation once per day makes the celestial sphere appear to turn, producing diurnal motion of stars. Revolution, precession, and proper motion operate on much longer timescales.

Question 7Astronomy

A lunar eclipse can occur only when the Moon is in which phase?

  1. Third quarter
  2. Full Moon Correct answer.
  3. First quarter
  4. New Moon

Explanation

A lunar eclipse happens when Earth passes between the Sun and the Moon, casting its shadow on the Moon. This geometry occurs only at full Moon, when the Moon is opposite the Sun.

Question 8Astronomy

The Hertzsprung-Russell diagram plots stars by luminosity against which quantity?

  1. Distance
  2. Surface temperature or spectral class Correct answer.
  3. Mass
  4. Age

Explanation

The H-R diagram uses luminosity (or absolute magnitude) on the vertical axis and temperature or spectral class on the horizontal axis. Stars cluster along the main sequence and in giant and dwarf regions.

Question 9Astronomy

A galaxy classified as a spiral typically has which combination of features?

  1. An irregular clumpy structure with no symmetry
  2. A central bulge, a flattened disk, and spiral arms Correct answer.
  3. A smooth ellipsoidal shape with no disk
  4. Only old stars in a spherical halo with no disk

Explanation

Spiral galaxies contain a central bulge, a rotating flattened disk, and spiral arms rich in gas and young stars. This distinguishes them from ellipticals and irregulars.

Question 10Astronomy

Astronomers infer the presence of dark matter in galaxies primarily because:

  1. Galaxies show no gravitational lensing
  2. The cosmic microwave background is uniform
  3. Rotation curves remain flat at large radii Correct answer.
  4. It emits strongly in visible light

Explanation

Observed rotation speeds of galaxies stay roughly constant far from the center, implying more mass than the visible stars and gas provide. This discrepancy is a key line of evidence for dark matter.

Question 11Astronomy

The cosmic microwave background radiation is best interpreted as:

  1. Relic radiation from the hot early universe Correct answer.
  2. Emission from interstellar dust
  3. Light from the first stars
  4. Synchrotron radiation from galaxies

Explanation

The CMB is relic radiation released when the universe cooled enough for neutral atoms to form, allowing photons to travel freely. Its near-perfect blackbody spectrum at about 2.7 K supports this interpretation.

Question 12Astronomy

A star with apparent magnitude 1 and a star with apparent magnitude 6 differ in brightness by roughly a factor of:

  1. 100 Correct answer.
  2. 1000
  3. 10
  4. 5

Explanation

The magnitude scale is logarithmic: a difference of 5 magnitudes corresponds to a brightness ratio of exactly 100. Therefore the magnitude 1 star is about 100 times brighter.

Question 13Astronomy

The main-sequence lifetime of a star is primarily determined by its:

  1. Rotation rate
  2. Color index alone
  3. Distance from Earth
  4. Mass Correct answer.

Explanation

More massive stars have far greater fuel reserves but consume them at a disproportionately higher rate, so they live shorter lives. Mass therefore dominates main-sequence lifetime.

Question 14Astronomy

The greenhouse effect on Venus has produced a surface environment characterized by:

  1. Extremely high surface temperature and pressure Correct answer.
  2. A thin cold atmosphere with liquid water
  3. A strong magnetic field shielding the surface
  4. Frequent liquid sulfuric acid rain reaching the ground

Explanation

Venus has a dense carbon dioxide atmosphere that traps heat, yielding surface temperatures around 460 degrees Celsius and pressures about 90 times Earth's. Sulfuric acid clouds evaporate before reaching the surface.

Question 15Astronomy

A comet's ion tail points away from the Sun because it is driven by:

  1. The comet's own outgassing momentum
  2. The comet's rotation
  3. Gravitational attraction to Jupiter
  4. Solar wind and radiation pressure Correct answer.

Explanation

The ion tail consists of charged particles pushed antisunward by the solar wind and radiation pressure, so it always points away from the Sun. The dust tail curves differently due to orbital motion.

Question 16Astronomy

The reason we always see the same face of the Moon from Earth is that the Moon:

  1. Orbits Earth once per day
  2. Does not rotate on its axis
  3. Rotates once per orbit around Earth Correct answer.
  4. Rotates twice per orbit around Earth

Explanation

The Moon is tidally locked: its rotation period equals its orbital period, so the same hemisphere always faces Earth. This is synchronous rotation, not an absence of rotation.

Question 17Astronomy

A newly discovered star shows strong hydrogen absorption lines and a surface temperature near 10,000 K. Its spectral class is most likely:

  1. A Correct answer.
  2. O
  3. G
  4. M

Explanation

A-type stars have surface temperatures near 7,500 to 10,000 K and exhibit their strongest hydrogen absorption lines. O stars are much hotter and M stars much cooler.

Question 18Astronomy

Two galaxies have the same intrinsic luminosity, but one appears 25 times fainter than the other. Using the inverse-square law, the fainter galaxy is approximately how many times farther away?

  1. 12.5
  2. 625
  3. 25
  4. 5 Correct answer.

Explanation

Apparent brightness falls as the inverse square of distance, so a brightness ratio of 25 corresponds to a distance ratio of the square root of 25, which is 5. The fainter galaxy is five times farther.

Question 19Astronomy

Earth's seasons arise primarily because:

  1. Earth's rotation rate changes seasonally
  2. The Sun's luminosity changes over the year
  3. Earth's rotational axis is tilted relative to its orbital plane Correct answer.
  4. Earth's distance from the Sun varies significantly

Explanation

The 23.5-degree tilt of Earth's axis changes the angle and duration of sunlight at each latitude through the year. Distance variations are relatively small and do not explain opposite seasons in the two hemispheres.

Question 20Astronomy

The cosmic distance ladder relies on parallax only for relatively nearby stars because:

  1. Distant stars do not exhibit proper motion
  2. Parallax measures brightness rather than distance
  3. Parallax angles become too small to measure accurately at great distances Correct answer.
  4. Distant stars do not emit visible light

Explanation

Parallax angle decreases with distance, and beyond a certain range the shift is smaller than observational uncertainty. Farther distances therefore require standard candles and other methods.

Question 21Astronomy

The Sun's energy is transported from the core to the surface through which sequence of zones?

  1. Radiative zone, then convective zone Correct answer.
  2. Convective zone, then radiative zone
  3. Photosphere, then core
  4. Corona, then chromosphere

Explanation

Energy generated in the core diffuses outward through the radiative zone and then is carried by convection through the outer convective zone to the photosphere. The order reflects the changing opacity and temperature gradient.

Question 22Astronomy

Observations of type Ia supernovae at high redshift led to which conclusion about the universe?

  1. It is static and unchanging
  2. It is contracting toward a big crunch
  3. Its expansion rate is exactly zero
  4. Its expansion is accelerating Correct answer.

Explanation

Distant type Ia supernovae appear fainter than expected for a decelerating universe, implying that cosmic expansion is speeding up. This acceleration is attributed to dark energy.

Question 23Astronomy

A main-sequence star of about 20 solar masses will most likely end its life as:

  1. A white dwarf
  2. A black hole Correct answer.
  3. A brown dwarf
  4. A planetary nebula with no remnant

Explanation

Very massive stars exhaust their fuel and collapse, and if the remnant exceeds the neutron-star limit, it forms a black hole. Lower-mass stars leave white dwarfs, while the most massive undergo core collapse.

Question 24Astronomy

The observed abundance of light elements such as helium and deuterium in the universe is best explained by:

  1. Supernova explosions in the recent past
  2. Cosmic ray spallation in interstellar space
  3. Stellar nucleosynthesis alone
  4. Big Bang nucleosynthesis in the first few minutes Correct answer.

Explanation

The roughly 25 percent helium abundance and the deuterium-to-hydrogen ratio match predictions of nucleosynthesis during the first few minutes after the Big Bang. Stellar processes cannot account for the primordial helium fraction.

Question 25Astronomy

A Cepheid variable's period is directly related to its luminosity, which allows astronomers to use it as a standard candle. This relationship is most useful because it lets observers determine a Cepheid's:

  1. Chemical composition directly
  2. Age from its pulsation amplitude
  3. Distance from its period and apparent brightness Correct answer.
  4. Surface temperature directly

Explanation

The period-luminosity relation gives intrinsic luminosity from the observed period, and combining that with apparent brightness yields distance. Cepheids therefore serve as key rungs on the distance ladder.

Question 26Astronomy

The celestial equator is best described as which of the following?

  1. The path the Sun traces against the background stars over a year
  2. The circle on the celestial sphere located 23.5 degrees from the celestial poles
  3. The great circle passing through the celestial poles and the observer's zenith
  4. The projection of Earth's equator onto the celestial sphere Correct answer.

Explanation

The celestial equator is the great circle on the celestial sphere that lies in the same plane as Earth's equator, so it is the projection of Earth's equator outward. The ecliptic is the Sun's annual path, and the meridian is the observer's north-south great circle. The circles 23.5 degrees from the poles are the tropics, not the celestial equator.

Question 27Astronomy

A star is observed to have a parallax angle of 0.1 arcsecond. What is its distance from Earth?

  1. 10 parsecs Correct answer.
  2. 100 parsecs
  3. 1 parsec
  4. 0.1 parsec

Explanation

Distance in parsecs is the reciprocal of the parallax angle in arcseconds, so d = 1/0.1 = 10 parsecs. A parallax of 1 arcsecond corresponds to 1 parsec, and smaller parallaxes correspond to larger distances. The other choices invert or misapply this relationship.

Question 28Astronomy

Which statement correctly describes the relationship between a star's color and its surface temperature?

  1. Bluer stars are hotter, following the pattern of blackbody radiation. Correct answer.
  2. Bluer stars are cooler because blue light has lower energy than red light.
  3. All stars have nearly the same color because they are all blackbodies.
  4. Color is unrelated to surface temperature and depends only on the star's mass.

Explanation

A star's continuous spectrum approximates a blackbody, and Wien's law shows that hotter blackbodies peak at shorter wavelengths. Therefore blue stars have higher surface temperatures than red stars. Color is not determined by mass alone, and blackbody colors vary strongly with temperature.

Question 29Astronomy

Which of the following is the most likely fate of a white dwarf that accretes enough mass to exceed the Chandrasekhar limit?

  1. It gradually cools and becomes a brown dwarf.
  2. It erupts as a type II supernova powered by core collapse.
  3. It explodes as a type Ia supernova, leaving no remnant. Correct answer.
  4. It collapses directly into a black hole without a visible explosion.

Explanation

A white dwarf supported by electron degeneracy pressure becomes unstable when its mass approaches about 1.4 solar masses. Carbon fusion ignites explosively, producing a type Ia supernova that disrupts the star completely. Type II supernovae instead arise from core collapse in massive stars.

Question 30Astronomy

Which of the following best describes the process of nuclear fusion in the core of the Sun?

  1. Hydrogen nuclei capture electrons to form neutrons and release energy.
  2. Carbon nuclei fuse to form iron, releasing energy.
  3. Four hydrogen nuclei combine to form one helium nucleus, releasing energy. Correct answer.
  4. One helium nucleus splits into four hydrogen nuclei, absorbing energy.

Explanation

The Sun's core converts hydrogen to helium mainly through the proton-proton chain, in which four protons effectively combine into one helium nucleus. The product has slightly less mass than the reactants, and the mass difference appears as energy. Fission and electron capture are not the dominant energy source in the Sun.

Question 31Astronomy

Which property of a telescope is most important for resolving fine detail in a distant galaxy?

  1. The magnification of the eyepiece
  2. The aperture diameter of the telescope Correct answer.
  3. The focal length of the telescope
  4. The light-gathering power of the human eye

Explanation

Angular resolution is limited by diffraction and improves as the aperture diameter increases, so a larger aperture resolves finer detail. Magnification and focal length affect image scale but cannot overcome the diffraction limit. The eye's light-gathering power is irrelevant to the telescope's resolution.

Question 32Astronomy

Which observation provided the first strong evidence that the universe is expanding?

  1. The measurement of redshifts in the spectra of distant galaxies Correct answer.
  2. The detection of the cosmic microwave background
  3. The discovery of quasars at large distances
  4. The observation of Cepheid variables in the Andromeda Galaxy

Explanation

Hubble's measurements of galaxy spectra showed that most galaxies have redshifts proportional to their distances, indicating expansion. The cosmic microwave background was discovered later and supports the hot Big Bang model. Quasars and Cepheids provided important distance and luminosity information but were not the first evidence for expansion.

Question 33Astronomy

Which of the following is a key characteristic of elliptical galaxies?

  1. They are composed mostly of old stars and have little interstellar gas. Correct answer.
  2. They are always smaller than dwarf irregular galaxies.
  3. They have prominent spiral arms and a central bar.
  4. They contain abundant cold gas and active star formation.

Explanation

Elliptical galaxies generally have smooth, featureless light profiles dominated by old stars, with little cold gas or ongoing star formation. Spiral arms and bars are characteristic of spiral galaxies. Ellipticals range widely in size and can be among the largest galaxies known.

Question 34Astronomy

A star's spectrum shows strong absorption lines of ionized calcium and neutral iron, and its surface temperature is about 5000 K. To which spectral class does this star most likely belong?

  1. O
  2. M
  3. B
  4. G Correct answer.

Explanation

G-type stars have surface temperatures near 5000 to 6000 K and show strong lines of ionized calcium and neutral metals such as iron. O and B stars are much hotter, and M stars are much cooler. The spectral features and temperature therefore point to a G star.

Question 35Astronomy

A star has a luminosity 100 times that of the Sun and a surface temperature twice that of the Sun. By what factor is its radius larger than the Sun's?

  1. 50
  2. 25
  3. 10
  4. 5 Correct answer.

Explanation

Luminosity scales as radius squared times temperature to the fourth power, so L/L_sun = (R/R_sun)^2 (T/T_sun)^4. Substituting 100 = (R/R_sun)^2 times 2^4 = 16 (R/R_sun)^2 gives (R/R_sun)^2 = 6.25, so R/R_sun = 2.5. The factor 5 is not correct because the temperature term is 16, not 4.

Question 36Astronomy

Which sequence correctly orders the stages in the evolution of a Sun-like star after it leaves the main sequence?

  1. Red giant, planetary nebula, white dwarf, protostar
  2. Main sequence, supernova, neutron star, white dwarf
  3. Red giant, white dwarf, planetary nebula, black hole
  4. Main sequence, red giant, planetary nebula, white dwarf Correct answer.

Explanation

A Sun-like star expands to a red giant after exhausting core hydrogen, then sheds its outer layers as a planetary nebula, leaving a white dwarf. Protostars precede the main sequence, and black holes or neutron stars are endpoints for much more massive stars. The correct order is therefore main sequence, red giant, planetary nebula, white dwarf.

Question 37Astronomy

The HR diagram shows a star cluster with a main sequence that turns off at a luminosity about 100 times the Sun's. What does this indicate about the cluster?

  1. The cluster contains no stars more massive than the Sun.
  2. The cluster is composed entirely of white dwarfs.
  3. The cluster is very young because massive stars are still on the main sequence. Correct answer.
  4. The cluster is very old because only low-mass stars remain on the main sequence.

Explanation

The main-sequence turnoff occurs where stars are just exhausting core hydrogen, and more massive stars evolve faster. A turnoff at high luminosity means massive stars are still on the main sequence, so the cluster is relatively young. An old cluster would have a turnoff at lower luminosity.

Question 38Astronomy

Which of the following best explains why the sky is dark at night in an infinite, static universe?

  1. The sky is dark because the universe is static and infinite, as observations confirm.
  2. The sky is dark because interstellar dust absorbs all starlight permanently.
  3. Olbers' paradox shows that an infinite static universe would have a bright sky, so the universe must be finite in age or expanding. Correct answer.
  4. The sky is dark because stars are uniformly distributed and infinitely old.

Explanation

Olbers' paradox notes that in an infinite, eternal, static universe every line of sight would end on a star, making the night sky bright. The observed darkness implies the universe has a finite age or is expanding, so light from distant regions has not had time to reach us. Dust absorption alone cannot solve the paradox because the dust would re-radiate the energy.

Question 39Astronomy

A galaxy is observed to have a redshift corresponding to a recession velocity of 6000 km/s. Using a Hubble constant of 70 km/s/Mpc, what is its approximate distance?

  1. 86 Mpc Correct answer.
  2. 42 Mpc
  3. 8.6 Mpc
  4. 420 Mpc

Explanation

Hubble's law states v = H0 times d, so d = v/H0 = 6000/70, which is approximately 86 Mpc. The other values result from misplacing the decimal or using the wrong operation. This calculation assumes a constant Hubble parameter and neglects peculiar velocities.

Question 40Astronomy

Which statement best describes the role of the cosmic microwave background in cosmology?

  1. It is emission from cold dust in the Milky Way and has no cosmological significance.
  2. It is the remnant radiation from the Big Bang, showing a nearly perfect blackbody spectrum with small temperature anisotropies. Correct answer.
  3. It is the light from the first generation of stars, redshifted into the microwave region.
  4. It is the energy released by supernovae throughout cosmic history.

Explanation

The cosmic microwave background is relic radiation from the hot, dense early universe, released when the universe became transparent. Its spectrum matches a blackbody at about 2.7 K, and its small anisotropies reveal density fluctuations. Starlight, dust emission, and supernova energy do not produce this uniform background.

Question 41Astronomy

Which of the following provides the strongest evidence that the universe is composed mostly of dark energy?

  1. The observed abundances of light elements from Big Bang nucleosynthesis
  2. The accelerated expansion inferred from distant type Ia supernovae Correct answer.
  3. The flat rotation curves of spiral galaxies
  4. The existence of the cosmic microwave background

Explanation

Distant type Ia supernovae appear fainter than expected in a decelerating universe, indicating that expansion is accelerating. This acceleration is attributed to dark energy. Light-element abundances and the CMB support the hot Big Bang, and flat rotation curves indicate dark matter rather than dark energy.

Question 42Astronomy

Which of the following best explains why the Moon exhibits phases as seen from Earth?

  1. Earth's shadow falls on different parts of the Moon during the month.
  2. The Moon rotates on its axis once per month, showing different faces.
  3. The Moon's orbital distance from Earth changes, altering its brightness.
  4. The angle between the Sun, Earth, and Moon changes as the Moon orbits Earth. Correct answer.

Explanation

The Moon shines by reflected sunlight, and as it orbits Earth the Sun-Earth-Moon angle changes, so we see different fractions of the illuminated hemisphere. Earth's shadow causes lunar eclipses, not the monthly phases. The Moon's rotation is synchronous, so it always shows the same face.

Question 43Astronomy

A solar eclipse can occur only when the Moon is in which phase?

  1. Third quarter
  2. First quarter
  3. New Moon Correct answer.
  4. Full Moon

Explanation

A solar eclipse occurs when the Moon passes between Earth and the Sun, which can happen only near new Moon. At full Moon the Moon is opposite the Sun and may produce a lunar eclipse. Quarter phases place the Moon at right angles to the Sun-Earth line.

Question 44Astronomy

Which of the following best explains why the same side of the Moon always faces Earth?

  1. Earth's gravity locks the Moon in place so it cannot rotate.
  2. The Moon rotates once per orbit, so its rotation period equals its orbital period. Correct answer.
  3. The Moon does not rotate on its axis.
  4. The Moon orbits Earth twice for every rotation it makes.

Explanation

The Moon is in synchronous rotation: it rotates once on its axis during each orbit around Earth, so the same hemisphere always faces us. It does rotate; the rotation is simply matched to the orbital period. Earth's gravity caused this tidal locking but does not prevent rotation.

Question 45Astronomy

Which of the following is the primary reason Venus has a much hotter surface than Mercury despite being farther from the Sun?

  1. Venus is more massive, so gravitational compression heats its surface.
  2. Venus has a thick carbon dioxide atmosphere that produces a strong greenhouse effect. Correct answer.
  3. Venus rotates more rapidly, generating internal heat.
  4. Venus has a higher albedo, so it absorbs more sunlight.

Explanation

Venus's dense carbon dioxide atmosphere traps infrared radiation through the greenhouse effect, raising its surface temperature to about 730 K. Mercury has almost no atmosphere and cannot retain heat in the same way. Rotation, albedo, and gravitational compression do not explain the extreme surface temperature.

Question 46Astronomy

Which of the following best explains why Mars has a thin atmosphere today?

  1. Mars's atmosphere condensed entirely into surface rocks.
  2. Mars's low gravity and lack of a global magnetic field allowed atmospheric gases to escape over time. Correct answer.
  3. Mars never had an atmosphere because it formed too far from the Sun.
  4. Mars's atmosphere was blown away by a nearby supernova.

Explanation

Mars has low escape velocity and lost its global magnetic field early, allowing solar wind and impacts to strip away much of its atmosphere. Geological evidence indicates Mars once had a thicker atmosphere and liquid water. Formation distance alone does not prevent an atmosphere from existing.

Question 47Astronomy

A comet is observed to have a blue ion tail and a curved yellowish dust tail. Which statement best explains why the two tails point in different directions?

  1. The ion tail is pulled toward the Sun by gravity, while the dust tail is pushed away.
  2. The dust tail points toward the Sun because dust particles are electrically charged.
  3. The ion tail is pushed directly away from the Sun by the solar wind, while the dust tail lags behind the comet's orbital motion. Correct answer.
  4. Both tails point in the same direction, and the difference in color is due to temperature.

Explanation

The ion tail consists of charged particles swept away from the Sun by the solar wind, so it points nearly radially outward. The dust tail consists of larger grains released from the nucleus that are pushed less strongly and tend to lag along the orbit, producing a curved shape. Gravity does not pull the ion tail toward the Sun.

Question 48Astronomy

Which of the following best explains why the Sun's corona is much hotter than its photosphere?

  1. The corona is heated by magnetic waves and reconnection events that deposit energy in the outer atmosphere. Correct answer.
  2. The corona is heated by nuclear fusion occurring in the photosphere.
  3. The corona is hotter because it contains more hydrogen than the photosphere.
  4. The corona is hotter because it is closer to the Sun's core.

Explanation

The corona reaches millions of kelvin while the photosphere is about 5800 K, and the energy must be transported outward non-thermally. Magnetic waves and magnetic reconnection are the leading mechanisms for depositing energy in the corona. The corona is farther from the core and has a similar composition to the photosphere.

Question 49Astronomy

A distant galaxy is observed with a redshift z = 1. What does this redshift imply about the wavelength of a spectral line that has a rest wavelength of 500 nm?

  1. The observed wavelength is 500 nm.
  2. The observed wavelength is 250 nm.
  3. The observed wavelength is 1500 nm.
  4. The observed wavelength is 1000 nm. Correct answer.

Explanation

Redshift is defined by 1 + z = observed wavelength divided by rest wavelength, so at z = 1 the observed wavelength is twice the rest wavelength. A rest wavelength of 500 nm therefore appears at 1000 nm. The other choices misapply the factor of 1 + z.

Question 50Astronomy

Which of the following best explains why type Ia supernovae are useful as standard candles for measuring cosmic distances?

  1. They are always associated with gamma-ray bursts, which have known distances.
  2. Their luminosity is directly proportional to their distance from Earth.
  3. They are the most common type of supernova and occur in every galaxy.
  4. They all have nearly the same peak luminosity because they arise from white dwarfs reaching a similar critical mass. Correct answer.

Explanation

Type Ia supernovae occur when a white dwarf approaches the Chandrasekhar limit, so their peak luminosities are similar and can be further calibrated using their light-curve shapes. This uniformity makes them useful standard candles. They are not the most common supernovae, and luminosity is not proportional to distance.