Astronomy Lesson Test: 40 General Science Questions

Answer: B

Correct answer: The Sun. A star is a ball of hot gas that produces its own energy by nuclear fusion, and the Sun is the only such object in our solar system. It holds about 99.8% of the solar system's mass, so its gravity keeps the planets in orbit. Jupiter can be a tempting pick because it is huge and mostly hydrogen, but it is far too small to sustain fusion.

• A: The Moon is Earth’s natural satellite.
• B (correct): The Sun is the star whose gravity dominates our solar system.
• C: Jupiter is a gas-giant planet.
• D: Earth is a planet, not the central star.

Answer: D

Correct answer: Mercury. The planets in order outward are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; a mnemonic such as "My Very Educated Mother Just Served Us Nachos" helps. Venus is the common wrong pick because it is the hottest planet, but its heat comes from a thick carbon dioxide atmosphere that traps energy. Mercury, despite being closest, has almost no atmosphere and loses heat rapidly at night.

• A: Jupiter is the fifth planet, lying beyond the asteroid belt.
• B: Mars is the fourth planet.
• C: Venus is the second planet.
• D (correct): Mercury is first in outward order from the Sun.

Answer: C

Correct answer: Mercury, Venus, Earth, Mars. Terrestrial planets are small, dense worlds with solid surfaces of rock and metal, and all four sit in the inner solar system. Near the young Sun it was too warm for ices to condense, so only rocky material built these planets. Beyond the asteroid belt, ices and gases were abundant, producing giant planets with no solid surface, so any list containing one is wrong.

• A: All four listed are giant outer planets.
• B: Jupiter and Saturn are giants, not terrestrial.
• C (correct): The four inner planets have solid rocky surfaces.
• D: Neptune is an ice giant.

Answer: C

Correct answer: Earth rotating on its axis. Earth spins once about every 24 hours, so at any moment half the planet faces the Sun in daylight while the other half is in night. The Sun appears to rise and set because we are carried around by that spin. Revolution is the common confusion, but one orbit around the Sun takes a full year and explains the calendar year, not a single day.

• A: Revolution defines the year, not the immediate daily alternation.
• B: The Sun does not orbit Earth once each day.
• C (correct): Rotation carries surface locations into and out of sunlight.
• D: Moon phases occur on a much longer cycle.

Answer: B

Correct answer: Earth’s tilted axis as it orbits the Sun. Earth's axis is tilted about 23.5° and keeps pointing the same way in space. When a hemisphere leans toward the Sun, it receives more direct sunlight and longer days, producing summer; six months later it leans away and gets winter. The tempting idea that distance matters fails because the hemispheres have opposite seasons at the same time, and Earth is closest to the Sun in January.

• A: Internal heating does not create the annual hemisphere pattern.
• B (correct): Axial tilt changes sunlight angle and day length through the year.
• C: Lunar distance is not the primary seasonal driver.
• D: The Sun does not switch its energy output off by season.

Answer: C

Correct answer: Meteor. The terms track the object's location: a meteoroid is a small rock in space, a meteor is the glowing streak when it rushes into the atmosphere and heats the air around it, and a meteorite is any piece that survives to land on the ground. A memory hook is that the meteorite reaches the earth's surface, ending in "-ite" like many rock names. Comets are icy bodies in orbit.

• A: Meteorite is a fragment that reaches the ground.
• B: An asteroid belt is a population in space, not a light streak.
• C (correct): Meteor refers to the visible atmospheric phenomenon.
• D: A comet is an icy object orbiting the Sun.

Answer: C

Correct answer: Distance light travels in one year. Despite the word year, a light-year measures length, not time, about 9.5 trillion kilometers or 5.9 trillion miles. Astronomers use it because star distances in ordinary units become unmanageably large; the nearest star beyond the Sun is roughly 4.2 light-years away. The trap is the word year, which suggests time, but it only tells you how long light needs to cover that distance.

• A: A light-year does not measure energy.
• B: An orbital year is a time interval, not a light-year distance.
• C (correct): Light-year is a length unit defined from light travel.
• D: Rotational speed is not what light-year denotes.

Answer: A

Correct answer: Earth. A moon, or natural satellite, orbits a planet, and Earth's gravity holds our Moon in an orbit taking about 27 days. The whole Earth–Moon system then orbits the Sun together, and the Sun in turn circles the center of the Milky Way. That nested motion explains the galaxy distractor: the Moon does move around the galactic center, but only by traveling along with Earth.

• A (correct): The Moon is Earth’s natural satellite.
• B: Mars has separate natural satellites.
• C: Jupiter has other moons, not Earth’s Moon.
• D: Both objects move through the galaxy, but the local orbital primary is Earth.

Answer: C

Correct answer: The Milky Way. A galaxy is an enormous system of stars, gas, dust, and dark matter held together by gravity, and ours is a barred spiral containing hundreds of billions of stars. The faint band of light across a dark night sky is our view of its disk from inside. Andromeda is the tempting wrong pick because it is the nearest large spiral galaxy, but it is a separate neighbor.

• A: The Kuiper Belt is part of the solar system.
• B: Orion Nebula is a star-forming region, not our entire galaxy.
• C (correct): The Milky Way contains our Sun and solar system.
• D: Andromeda is a separate neighboring galaxy.

Answer: C

Correct answer: Pluto. In 2006 the International Astronomical Union defined a planet as a body that orbits the Sun, is massive enough to be nearly round, and has cleared its orbital neighborhood of other objects. Pluto meets the first two criteria but shares its region with many Kuiper Belt objects, so it is classified as a dwarf planet. Neptune, though farthest, is a major planet.

• A: Saturn is a gas-giant major planet.
• B: Uranus is an ice-giant major planet.
• C (correct): Pluto is officially classified as a dwarf planet.
• D: Neptune is the eighth recognized major planet.

Answer: A

Correct answer: Mercury, Venus, Earth, Mars. Ordering outward from the Sun, Mercury is first, Venus second, Earth third, and Mars fourth. A mnemonic such as "My Very Educated Mother" fixes this order, and the full sentence continues through the outer planets. Errors usually come from swapping Mercury and Venus, since Venus is brighter and more familiar, or from putting Earth first because it is our own reference point.

• A (correct): The inner four are Mercury, Venus, Earth and Mars.
• B: Earth is not first among these planets.
• C: Mercury lies closer to the Sun than Venus.
• D: Venus is between Mercury and Earth.

Answer: A

Correct answer: The Moon lies approximately between Earth and Sun. In that position the Sun lights the Moon's far side, so the half facing Earth is dark and nearly invisible, and the Moon rises and sets with the Sun. Full moon is the reverse, with Earth roughly in the middle. If the alignment is exact at new moon, the Moon's shadow falls on Earth and causes a solar eclipse.

• A (correct): New moon means the Moon’s sunlit side is mostly away from Earth.
• B: Earth in the middle describes the approximate full-moon arrangement.
• C: The Moon moving through Earth’s shadow is a lunar eclipse, which happens near full moon.
• D: The Sun is not between Earth and its Moon.

Answer: C

Correct answer: Changing view of the Moon’s sunlit half. The Sun always lights half of the Moon, but as the Moon orbits Earth over about a month, we see different amounts of that lit half. Facing us fully gives a full moon; facing away gives a new moon. The common misconception blames Earth's shadow, but the shadow only reaches the Moon during lunar eclipses, which are rare and happen only at full moon.

• A: The Moon reflects sunlight; it is not a switching lamp.
• B: Clouds on Earth may block the view but do not cause the ordered phase cycle.
• C (correct): The visible fraction of the illuminated hemisphere changes during orbit.
• D: Earth’s shadow is special to lunar eclipses.

Answer: D

Correct answer: The Moon. A solar eclipse needs the order Sun, Moon, Earth, which can happen only at new moon. The Moon is about 400 times smaller than the Sun but also about 400 times closer, so the two look nearly the same size and the Moon can just cover the solar disk. Venus and Mercury sometimes cross the Sun, but they appear as tiny dots, called transits.

• A: Earth cannot lie between itself and the Sun.
• B: Venus transits are not ordinary solar eclipses caused by the Moon.
• C: Jupiter does not regularly cast the Moon’s eclipse shadow on Earth.
• D (correct): The Moon can block direct sunlight and cast a shadow on Earth.

Answer: B

Correct answer: Sunlight filtered through Earth’s atmosphere reaches the Moon. During a total lunar eclipse, Earth blocks direct sunlight, but its atmosphere bends some light into the shadow. On the way, air scatters away blue light more strongly, the same effect that makes sunsets red, so mostly red and orange light reaches the Moon. In effect, the Moon is lit by every sunrise and sunset on Earth at once.

• A: The Moon does not sustain stellar core fusion.
• B (correct): Earth’s atmosphere preferentially transmits and bends reddish sunlight into the shadow.
• C: The Moon remains a rocky satellite, not a star.
• D: Light reflected from distant Mars is far too faint to color the eclipsed Moon.

Answer: B

Correct answer: The lunar orbital plane is tilted relative to Earth’s orbital plane. The tilt is about 5°, so at most new and full moons the Moon passes slightly above or below the Sun–Earth line and its shadow misses Earth, or Earth's shadow misses it. Eclipses happen only when a new or full moon falls near one of the two points where the orbits cross, which occurs in eclipse seasons roughly every six months.

• A: Rotation continues every day.
• B (correct): The Moon usually passes above or below the required exact alignment.
• C: The Moon remains in orbit throughout its monthly cycle.
• D: The Sun emits light continuously on human timescales.

Answer: A

Correct answer: New and full moon. At both phases the Sun, Earth, and Moon lie nearly in a straight line, so the Sun's tidal pull adds to the Moon's and the tidal range is greatest. It does not matter whether the Moon is between Earth and Sun or on the far side, because each body raises bulges on both sides of Earth. At quarter phases the pulls are at right angles, producing weaker neap tides.

• A (correct): Sun-Moon alignment near new/full increases tidal range in the simple model.
• B: A waxing crescent does not give the strongest basic Sun-Moon alignment.
• C: Quarter phases generally favor neap tides.
• D: The equinox is unrelated to the defining lunar alignment.

Answer: B

Correct answer: Mars and Jupiter. The main belt holds millions of rocky and metallic bodies orbiting the Sun in the gap between the inner rocky planets and the giant planets. Jupiter's strong gravity kept this material from gathering into a full planet. The belt also marks a handy dividing line: everything inside it is terrestrial, and everything beyond it is a giant. Despite movie images, asteroids are typically very far apart.

• A: This region is interior to the main asteroid belt.
• B (correct): The main asteroid belt occupies the Mars-Jupiter region.
• C: Jupiter-Saturn is farther out than the main belt.
• D: Uranus-Neptune is in the outer solar system, not the main belt.

Answer: D

Correct answer: Solar heating releasing gas and dust from the nucleus. A comet's nucleus is a frozen mix of ices, rock, and dust, often called a dirty snowball. Far from the Sun it stays inactive, but as it approaches, sunlight warms the ices so they turn directly into gas, carrying dust with them. This forms the glowing coma, which sunlight and the solar wind then push into tails. Comets shine by reflected and re-emitted sunlight, not fusion.

• A: Approaching the Sun does not convert a comet to a planet.
• B: Comets are far too small to sustain nuclear fusion; their glow comes from sunlight acting on released gas and dust.
• C: An Earth volcano cannot create a comet tail.
• D (correct): Solar heating drives sublimation and dust/gas release.

Answer: A

Correct answer: They generally point away from the Sun due to solar effects. The solar wind sweeps the ion tail straight outward, and sunlight's radiation pressure pushes the dust tail along a curved path. Because these forces act away from the Sun, a comet leaving the inner solar system actually travels tail-first. The tempting error is picturing a tail trailing behind like exhaust; its direction depends on the Sun's position, not the comet's motion.

• A (correct): Solar wind and radiation pressure generally drive tails anti-sunward.
• B: Solar wind and radiation push tail material generally away from the Sun.
• C: Far from the Sun many comets have no prominent visible tails.
• D: A tail’s direction need not be directly opposite the motion.

Answer: D

Correct answer: Uranus and Neptune. Astronomers call them ice giants because much of their mass consists of water, ammonia, and methane, compounds called ices by planetary scientists, even though they exist mostly as hot, dense fluids inside. Jupiter and Saturn, by contrast, are mostly hydrogen and helium and are called gas giants. Methane in the upper atmospheres of Uranus and Neptune absorbs red light, giving them their bluish color.

• A: Jupiter and Saturn are generally described as gas giants.
• B: Earth and Mars are rocky terrestrial planets.
• C: Both Mercury and Venus are rocky terrestrial planets.
• D (correct): Uranus and Neptune are the two ice giants.

Answer: D

Correct answer: 1,200,000 km. Distance equals speed multiplied by time: 300,000 km/s × 4 s = 1,200,000 km, and the seconds cancel, leaving kilometers. Radio waves are electromagnetic waves, so in vacuum they travel at the speed of light. Checking the units protects against the common errors of dividing or misplacing a zero. For scale, the Moon averages about 384,000 km away, so a radio signal reaches it in under 1.3 seconds.

• A: This comes from dividing instead of multiplying.
• B: This is ten times the correct distance.
• C: That is the distance for only one second.
• D (correct): Distance = 300,000 $\frac{\mathrm{km}}{\mathrm{s}}$ × 4 s = 1,200,000 km.

Answer: A

Correct answer: Light takes time to cross the Sun-Earth distance. Light moves about 300,000 km per second, and the Sun is about 150 million km away, so the trip takes roughly 500 seconds, a little over eight minutes. Everything we see in space is therefore a view of the past, and the farther the object, the older the image. Distant galaxies appear as they were millions or billions of years ago.

• A (correct): Light travels a finite distance each second, delaying information.
• B: The Sun produces nearly continuous radiation.
• C: Atmospheric storage is not the cause.
• D: The Moon does not generally block and release the Sun’s light on a timer.

Answer: D

Correct answer: Reflecting—mirror; refracting—lens. Use the root words: reflection is light bouncing off a surface, so a reflector gathers light with a curved mirror, while refraction is light bending as it passes through a material, so a refractor uses a lens. Large research telescopes are reflectors because big mirrors can be supported from behind, while large lenses sag under their own weight and split colors.

• A: The two key focusing components are reversed.
• B: Prisms and radio antennas are not these core optical definitions.
• C: Microphones and magnets are not the distinguishing components.
• D (correct): Reflecting telescopes use mirrors; refractors use lenses.

Answer: B

Correct answer: Hydrogen fusion into helium. In the core, extreme temperature and pressure force hydrogen nuclei together to form helium. A helium nucleus has slightly less mass than the nuclei that formed it, and that missing mass becomes energy according to E = mc². Combustion is the tempting misconception, but ordinary chemical burning would have used up the Sun in thousands of years, not the billions it has already shone.

• A: Earth cannot supply the Sun’s core energy.
• B (correct): Fusion converts lighter hydrogen nuclei into helium, releasing energy.
• C: Combustion is not the Sun’s principal source.
• D: Ordinary burning is neither stellar fission nor fusion.

Answer: B

Correct answer: A blue-white star. Hotter objects emit most of their light at shorter wavelengths, so as temperature rises, the peak color shifts from red toward yellow, white, and blue. You can see the same idea in a heated metal bar that glows dull red, then orange, then nearly white as it gets hotter. Red stars may look fiery, but red indicates the coolest stellar surfaces.

• A: Red stars are generally cooler at their surfaces.
• B (correct): Blue-white stellar light generally indicates a hotter surface than red.
• C: Stellar color provides temperature information, though other properties matter.
• D: Different colors indicate different characteristic temperatures.

Answer: D

Correct answer: Light received from an object by an observer. Apparent brightness is how bright an object looks from where you are, which depends both on how much light it emits and on how far away it is. Light spreads out as it travels, so brightness falls with the square of distance. The trap is confusing it with luminosity, the total power a star emits, which stays the same no matter where the observer is.

• A: Mass-loss fraction does not define brightness.
• B: That is luminosity, not apparent brightness.
• C: Identical stars appear dimmer at greater distances.
• D (correct): Apparent brightness depends on received light and distance.

Answer: C

Correct answer: Core hydrogen fusion. In a main-sequence star, enormous pressure and temperature in the core force hydrogen nuclei to fuse into helium, releasing energy that pushes outward and balances gravity. That balance keeps the star stable for most of its life, which is why most stars we see, including the Sun, are on the main sequence. Reflected light is how planets and moons shine, not stars, and stars are hot plasma with no solid crust.

• A: Evaporation is not the chief energy source of stars.
• B: Stars generate much of their own radiation.
• C (correct): Main-sequence stars fuse hydrogen in their cores.
• D: Stars are plasma/gas objects, not solid rocky planets.

Answer: C

Correct answer: It orbits a star outside our solar system. The prefix exo- means outside, so an exoplanet is any planet whose host star is not the Sun. Distant objects that still orbit the Sun, such as dwarf planets beyond Neptune, belong to our own solar system no matter how far out they are. Moons are not planets at all, because they orbit a planet rather than a star. Thousands of exoplanets have now been found, mostly by the dimming they cause or the wobble they induce in their stars.

• A: Bodies orbiting the Sun are within our solar system.
• B: A planet is not defined as an atmospheric object.
• C (correct): An exoplanet belongs to a planetary system beyond our own.
• D: A Jovian moon is a satellite, not an exoplanet.

Answer: A

Correct answer: Liquid surface water may be possible. The habitable zone is the range of distances where a planet receiving its star's light could have temperatures that allow liquid water on its surface. It describes only distance and energy received, so it sets a possibility, not a guarantee. Whether water actually exists depends on the planet's atmosphere, mass and history, none of which distance reveals. The common mistake is to treat the zone as evidence of life; it only marks where conditions could permit it.

• A (correct): The zone marks distances where liquid water could exist, which is a possibility, not a guarantee.
• B: Red dwarf stars also have habitable zones, just closer in.
• C: Habitable-zone location alone is not evidence of life.
• D: Atmosphere and air pressure cannot be inferred from orbital distance alone.

Answer: B

Correct answer: 500 seconds. Travel time equals distance divided by speed, so divide 150,000,000 km by 300,000 km/s. A quick way to check is to cancel zeros: 150,000,000 ÷ 300,000 is the same as 1,500 ÷ 3, which is 500. Dividing by 60 gives a little over 8 minutes, a figure worth remembering: the sunlight you see left the Sun about 8 minutes earlier. Answers off by a factor of ten usually come from miscounting zeros.

• A: 5,000 seconds is ten times too large.
• B (correct): 150,000,000 ÷ 300,000 = 500 seconds, about 8 minutes 20 seconds.
• C: 50 seconds corresponds to only 15 million kilometers.
• D: 50,000 seconds is one hundred times too large.

Answer: A

Correct answer: 24 years since emission. A light-year is a distance, not a time: it is how far light travels in one year, about 9.5 trillion km. So a star 24 light-years away sends light that needs 24 years to reach us, and we see the star as it was 24 years ago. The tempting error is reading light-year as a unit of time or mixing it up with light-hours. Looking at distant objects is always looking into the past.

• A (correct): Light took about 24 years to cover 24 light-years.
• B: One month is not the travel time for 24 light-years.
• C: A millionfold factor is not given or justified.
• D: Light-year does not mean light-hour.

Answer: D

Correct answer: One ninth as bright. Light from a star spreads over the surface of an ever-larger sphere, and a sphere's area grows with the square of its radius. Tripling the distance spreads the same light over 3² = 9 times the area, so each square meter receives one ninth as much. The common mistake is assuming brightness drops in simple proportion to distance, which would give one third. The same inverse-square rule applies to gravity and to sound spreading in open air.

• A: This reverses the inverse-square relationship.
• B: This incorrectly uses a linear, not square, dependence.
• C: Farther distance reduces, rather than increases, received brightness.
• D (correct): Inverse-square spreading gives relative brightness $\frac{1}{3}$² = $\frac{1}{9}$.

Answer: B

Correct answer: Main sequence → red giant → white dwarf. When a Sun-like star uses up the hydrogen in its core, the core contracts while the outer layers expand and cool, making a red giant. Later the star sheds its outer layers, and the exposed hot core remains as a dense, Earth-sized white dwarf that slowly cools. Supernovae, neutron stars and black holes require stars roughly eight or more times the Sun's mass, so they do not fit a star like the Sun.

• A: The Sun is not massive enough for the usual core-collapse pathway.
• B (correct): Sun-like stars swell as red giants and leave white-dwarf remnants.
• C: A white dwarf does not normally become a gas giant and then a star.
• D: A neutron star normally comes from massive-star core collapse.

Answer: A

Correct answer: Approximately 18 days. A transit happens when a planet passes in front of its star, blocking a little light. Because the planet crosses once per orbit, the time between matching dips equals the orbital period. If the dips repeat every 18 days and come from a single planet, that planet circles its star every 18 days. Doubling or halving the interval would require extra assumptions, such as missed transits or a second body, which the observation does not support.

• A (correct): The interval between comparable transits suggests an 18-day orbit.
• B: The observed repetition is measured in days, not years.
• C: Twice the repetition interval is not the simplest single-planet model.
• D: Half-period is not supported by one transit per orbital revolution.

Answer: D

Correct answer: Long daylight and relatively high midday Sun angle. Seasons come from Earth's axial tilt of about 23.5°, not from changing distance to the Sun. At the June solstice the Northern Hemisphere tilts toward the Sun, so the Sun climbs higher at noon and stays above the horizon longer, giving the longest day of the year at 45° N. The Southern Hemisphere has the opposite: its shortest days. Earth is actually near its farthest from the Sun in early July, which shows distance is not the cause.

• A: Distance does not produce polar night at 45° N.
• B: Corresponding southern latitude has opposite seasonal daylight pattern.
• C: These conditions fit northern winter much better.
• D (correct): Northern midlatitudes receive extended daylight and high Sun angles near June solstice.

Answer: D

Correct answer: Lunar eclipse near full moon. A lunar eclipse needs Earth between the Sun and Moon, so Earth's shadow can fall on the Moon. That same lineup is what makes a full moon, which is why lunar eclipses happen only at full moon. They do not happen every month because the Moon's orbit is tilted about 5° and usually passes above or below the shadow. A solar eclipse is the reverse arrangement, with the Moon in the middle at new moon.

• A: Solar eclipse places the Moon between Earth and the Sun.
• B: New moon places the Moon toward the Sun from Earth’s perspective.
• C: First-quarter geometry differs from direct opposition.
• D (correct): Earth in the middle can cast its shadow onto a full Moon.

Answer: B

Correct answer: The craft and astronauts are falling together around Earth. At low orbital altitudes, gravity is still roughly 90 percent as strong as at the surface. The spacecraft stays in orbit because it moves sideways so fast that, as it falls, Earth's surface curves away beneath it. Since the astronauts and the craft fall at the same rate, nothing presses them against the floor, so they feel weightless. The misconception that space has no gravity fails because gravity is exactly what keeps the craft in orbit.

• A: Earth’s gravity remains substantial at low orbital heights.
• B (correct): Shared orbital free fall causes the apparent weightless condition.
• C: Ordinary spacecraft walls cannot shield gravitational fields.
• D: The Moon does not cancel gravity along entire low Earth orbits.

Answer: C

Correct answer: The farther planet generally has the longer orbital period. A more distant planet has a much longer path to travel, and the star's gravity is weaker there, so the planet also moves more slowly. Both effects lengthen the year. Kepler's third law states this precisely: the square of the period is proportional to the cube of the orbit's size. In our solar system, Mercury orbits in 88 days while Neptune takes about 165 years. Orbital period should not be confused with rotation, which is the length of a day.

• A: Different orbital radii generally mean different periods.
• B: Axial rotation is not determined directly by orbital radius.
• C (correct): For a shared central mass, more distant orbits usually take longer.
• D: This reverses the usual distance–orbital-period relation.

Answer: A

Correct answer: Space expansion stretches the light wavelengths during travel. In cosmological redshift, the space between galaxies expands while the light is in transit, so each wave is stretched to a longer, redder wavelength. The longer the trip, the more stretching, which is why more distant galaxies show larger redshifts, the pattern Hubble observed. Redshift means a shift toward longer wavelengths, never toward blue. Gravitationally bound systems such as the solar system and the Milky Way do not expand with space.

• A (correct): Cosmological redshift is consistent with wavelengths stretched as space expands.
• B: Stretching shifts toward longer wavelengths, not systematically toward blue.
• C: Galaxies outside the Milky Way exist independently.
• D: Bound local systems do not simply scale up at cosmic expansion rates.

Answer: D

Correct answer: Neptune. The Kuiper Belt is the icy outer region beyond Neptune, home to Pluto and many similar bodies. Do not confuse it with the main asteroid belt, which lies mostly between Mars and Jupiter.

• A: Beyond Mars lies the main asteroid belt of rocky bodies, which is a different region from the Kuiper Belt.
• B: Jupiter marks the outer edge of the main asteroid belt, not the start of the icy Kuiper Belt.
• C: Nothing like the Kuiper Belt sits just past Earth; the next planet out is Mars.
• D (correct): The Kuiper Belt is an outer region of icy objects past the eighth planet, Neptune.

Answer: B

Correct answer: About 10 minutes. One-way time is distance divided by speed: 90,000,000 km ÷ 300,000 km/s = 300 s.

The signal must go out and the reply must come back, so the total is 2 × 300 s = 600 s. Dividing by 60 gives 10 minutes.

• A: This is the one-way travel time only; the reply must also cross the same 90 million km back to Earth.
• B (correct): Each leg takes 300 s, so the round trip is 600 s, which is 10 minutes.
• C: This treats the 600 s round-trip time as if it were already in minutes instead of dividing by 60.
• D: This doubles the round-trip time a second time, counting each leg twice.

Answer: B

Correct answer: Star Y is 2 times as far away. For equal light output, apparent brightness varies with 1 divided by distance squared. Brightness 1/4 as great means the distance squared is 4 times as great, so the distance is

times as great.

• A: This assumes brightness drops in direct proportion to distance, but it drops with the square of distance.
• B (correct): Brightness falls with the square of distance, and 2 squared is 4, matching one quarter the brightness.
• C: This squares the brightness ratio instead of taking its square root.
• D: A closer star of equal power would look brighter, not dimmer.

Answer: C

Correct answer: Waxing gibbous. The cycle runs new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent. Waxing means the visible lit portion is growing, so the phase right after first quarter is waxing gibbous.

• A: A waning crescent comes late in the cycle, after third quarter, when the lit part is shrinking.
• B: New moon begins the cycle; the lit part keeps growing after first quarter rather than vanishing.
• C (correct): After first quarter the visible lit portion keeps increasing, so more than half but not all of the disk appears lit.
• D: Third quarter is the half-lit phase that follows full moon, when the lit part is shrinking.

Answer: A

Correct answer: Jupiter. Jupiter and Saturn are gas giants, and Jupiter is the largest planet of all. Rings, distance from the Sun or being the biggest rocky planet do not decide overall size.

• A (correct): Jupiter, a gas giant, is the biggest planet in the solar system.
• B: Saturn is a large gas giant famous for its rings, but it is smaller than Jupiter.
• C: Neptune is the farthest planet, but being farthest does not make it the largest.
• D: Earth is the largest of the rocky inner planets, yet it is tiny next to the giant planets.

Answer: B

Correct answer: Neap tides with a smaller range. Near first and third quarter the Sun and Moon pull at roughly right angles, so their tide-raising effects partly offset. The result is neap tides, with a smaller difference between high and low water than near new or full moon.

• A: Spring tides come near new and full moon, when the Sun and Moon line up and their effects add.
• B (correct): At right angles the Sun's and Moon's tidal effects partly cancel, so the gap between high and low water shrinks.
• C: The Moon and Sun still produce tidal forces at quarter phases; the range is only reduced.
• D: The word spring in spring tide refers to a strong tidal range, not the season of the year.

Answer: D

Correct answer: A meteorite. The same body has different names at different stages: a meteoroid in space, a meteor as it glows in the atmosphere, and a meteorite if a piece lands and is found.

• A: A meteor is the bright streak of light seen in the sky, not the object found on the ground.
• B: A meteoroid is the name for the body while it is still traveling in space.
• C: A comet is an icy body orbiting the Sun, not a rock recovered from the ground.
• D (correct): A fragment from space that survives entry and reaches the ground is a meteorite.

Answer: D

Correct answer: When it is summer in Australia, it is winter in Canada at the same time. If distance controlled seasons, the whole planet would have the same season at the same time. Opposite seasons in the two hemispheres on the same date show that the tilt of Earth's axis, which aims one hemisphere toward the Sun and the other away, is the main cause.

• A: An oval orbit does change the distance a little, so this fact seems to support the claim rather than disprove it.
• B: This describes a feature of the seasonal cycle but does not test whether distance causes it.
• C: Polar cold comes from low sunlight angles and says nothing directly about Earth-Sun distance changes.
• D (correct): Both hemispheres are the same distance from the Sun on any date, so distance cannot give them opposite seasons at once.

Answer: C

Correct answer: Its core will collapse in a supernova, leaving a neutron star or black hole. A star's fate depends mainly on its mass. Sun-like stars become red giants and then white dwarfs, but a star of about 20 solar masses ends with core collapse and a supernova, leaving a neutron star or black hole.

• A: That gentle path fits stars of roughly the Sun's mass, not stars many times more massive.
• B: No star fuses hydrogen forever, and more massive stars actually use up their core fuel faster.
• C (correct): Very massive stars end in core collapse, and the remnant is a neutron star or black hole.
• D: A star's remnant does not become a planet; planets form differently and shine by reflected light.

Answer: A

Correct answer: It moves faster, and sunlight heating its nucleus makes a coma and tails likely. In an elliptical orbit, a body moves faster near the Sun and slower far away. Close to the Sun, sunlight warms the icy nucleus so gas and dust escape, forming a coma and tails that point generally away from the Sun. Far out and cold, the comet may show no tail at all.

• A (correct): Objects in elliptical orbits move fastest nearest the Sun, and solar heating there drives off gas and dust.
• B: The pull is strongest near the Sun, and the comet is moving fastest there, not slowest.
• C: Only an ideal circular orbit keeps constant speed; elliptical orbits speed up near the Sun.
• D: The speed part is right, but comet tails point generally away from the Sun, not simply behind the comet's motion.

Answer: C

Correct answer: Radio waves are electromagnetic and can cross a vacuum, while sound needs a medium. Radio waves, like visible light, belong to the electromagnetic spectrum and can travel through a vacuum. Sound is a mechanical wave that needs a material medium, so it cannot cross the nearly empty space between galaxies.

• A: Radio waves are electromagnetic radiation, not sound; this confuses two different kinds of waves.
• B: Sound is far slower than light, and it never crosses empty space in the first place.
• C (correct): Electromagnetic waves travel through empty space, but sound requires matter to carry its vibrations.
• D: Distance is not the issue; sound cannot travel across the near-vacuum of space at any distance.