128 Space Trivia Questions and Answers
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Easy Space Trivia Questions
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Which mission first landed humans on the Moon?
Apollo 11
NASA's Apollo 11 mission made the first crewed lunar landing in July 1969.
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In which lunar sea did Apollo 11 land?
Sea of Tranquility (Mare Tranquillitatis)
Armstrong and Aldrin set down on 20 July 1969 in the Sea of Tranquility, and named the spot Tranquility Base. The Moon's dark 'seas' hold no water at all: they are vast plains of basalt left by lava floods more than three billion years ago.
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In what year did Apollo 11 land humans on the Moon?
1969
Apollo 11 landed in 1969, fulfilling President John F. Kennedy's goal of sending humans to the Moon and returning them safely before the decade ended.
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The main asteroid belt lies between which two planets?
Mars and Jupiter
The main asteroid belt occupies the region between Mars and Jupiter. Jupiter's strong gravity helped prevent the material there from forming another planet.
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Who was the first American to orbit Earth?
John Glenn
John Glenn circled Earth three times aboard Friendship 7 on 20 February 1962. Alan Shepard and Gus Grissom had flown before him in 1961, but those were suborbital hops that went up and straight back down.
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An astronomical unit is approximately how far?
About 150 million kilometers
One astronomical unit, or AU, is the average distance between Earth and the Sun: about 149.6 million kilometers. Astronomers use it for distances within planetary systems.
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What is the standard cosmological model called in which the universe expands from an early hot, dense state?
Big Bang
The Big Bang model describes an early hot, dense universe expanding and cooling; it is not an explosion from one central place.
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What is the boundary around a black hole beyond which light cannot escape called?
Event horizon
The event horizon marks the point of no return around a black hole. An accretion disk is the hot material that may orbit outside it, while the singularity is predicted to lie deeper inside.
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Which constellation is marked by five bright stars forming a rough zigzag?
Cassiopeia
Five prominent stars in Cassiopeia form a distinctive W or M shape.
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What is a typical comet nucleus made of?
Frozen gases, rock, and dust
A comet nucleus is a solid mixture of frozen gases, rock, and dust. When heated near the Sun, it can produce a coma and tail.
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In which direction does a comet's ion tail point?
Away from the Sun
A comet’s ion tail points away from the Sun because the solar wind carries charged gas outward. Unlike the dust tail, it usually points almost directly away from the Sun even as the comet moves along its orbit.
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Which planet is third from the Sun?
Earth
Earth is the third planet outward from the Sun.
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Which planet in the Solar System is not named after a Greek or Roman god?
Earth
Earth's name is Germanic and simply means ground or soil. Every other planet carries the name of a Roman deity, apart from Uranus, which kept its Greek one.
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A star's brightness dips a fraction of a percent every few days, then recovers. What does that reveal?
A planet crossing in front of it
This is called the transit method: the depth of the dip reveals the planet's size relative to its star, and the interval between dips gives its orbital period. NASA's Kepler telescope used the technique to confirm more than 2,000 exoplanets before retiring in 2018.
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Who was the first human to travel into space?
Yuri Gagarin
Soviet cosmonaut Yuri Gagarin became the first human in space on April 12, 1961, completing one orbit of Earth aboard Vostok 1.
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Who was the first person to step onto the Moon?
Neil Armstrong
Neil Armstrong stepped onto the lunar surface during Apollo 11 on July 20, 1969. Buzz Aldrin followed him shortly afterward.
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Who performed the first spacewalk?
Alexei Leonov
Leonov left the Voskhod 2 spacecraft in 1965 for the first extravehicular activity. Ed White performed the first American spacewalk later that year.
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Who became the first woman in space?
Valentina Tereshkova
Tereshkova flew aboard Vostok 6 in 1963. Sally Ride later became the first American woman in space, while Savitskaya was the first woman to perform a spacewalk.
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In which galaxy is our solar system?
Milky Way
The Sun is one of a few hundred billion stars in the Milky Way, a barred spiral roughly 100,000 light years across, sitting about halfway out from the centre. The pale band that crosses a dark night sky is the massed light of the galaxy's own disc, seen edge on from inside it.
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A satellite in geostationary orbit takes approximately how long to orbit Earth?
24 hours
A geostationary satellite orbits once in about 24 hours, matching Earth's rotation. When positioned above the equator, it appears to hover over one longitude.
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The Great Red Spot is a giant storm on which planet?
Jupiter
The Great Red Spot is a long-lived anticyclonic storm in Jupiter's atmosphere. It has been observed for centuries, although its size has changed.
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About how long is Halley's Comet's average orbital period?
About 76 years
Halley's Comet returns to the inner Solar System about every 75 to 76 years. Its next perihelion after 1986 is expected in 2061.
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Which planet has the hottest average surface temperature?
Venus
Venus has the hottest average surface temperature of any planet, reaching about 465°C (870°F). Its thick carbon-dioxide atmosphere traps heat through an intense greenhouse effect.
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In what year was the Hubble Space Telescope launched?
1990
The Space Shuttle Discovery deployed Hubble in April 1990. Its position above most of Earth's atmosphere lets it take exceptionally sharp images in visible and other wavelengths.
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What element is produced when the Sun fuses hydrogen in its core?
Helium
The Sun's main energy-producing chain combines hydrogen nuclei into helium. A small amount of mass is converted into energy during the process.
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Which space telescope was designed mainly to observe infrared light?
James Webb Space Telescope
The James Webb Space Telescope works in the infrared, which lets it see through dust clouds and catch light from the universe's earliest galaxies, stretched to longer wavelengths by the expansion of space. A five-layer sunshield the size of a tennis court keeps it cold enough to register those faint signals.
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In what year was the James Webb Space Telescope launched?
2021
The James Webb Space Telescope launched on December 25, 2021. It observes mainly infrared light and operates near the Sun-Earth L2 point.
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Which gas is the main component of Jupiter's atmosphere?
Hydrogen
Jupiter's atmosphere is mostly molecular hydrogen, with helium making up most of the remainder. Trace compounds such as ammonia help create its visible cloud bands.
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Which moon is the most volcanically active body in the solar system?
Io
Jupiter's gravity flexes Io as it orbits, and the friction of that constant kneading keeps hundreds of volcanoes erupting. Some throw sulphur plumes hundreds of kilometres above the surface.
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The Kuiper Belt lies where in the Solar System?
Beyond Neptune
The Kuiper Belt is a broad region of icy bodies beyond Neptune’s orbit. It contains dwarf planets such as Pluto and is a remnant of the Solar System’s formation.
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Which is the largest structure humans have ever assembled in space?
International Space Station
The International Space Station spans roughly the area of a football field including its solar arrays, and it took more than thirty assembly flights to build. It has been continuously crewed since November 2000.
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Which planet is the largest in our Solar System?
Jupiter
Jupiter is the largest planet by both diameter and mass. Its volume is large enough to contain more than 1,300 Earths.
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What is the largest moon in the Solar System?
Ganymede
Ganymede, which orbits Jupiter, is larger in diameter than the planet Mercury, although it has much less mass. It is also the only moon known to have its own magnetic field.
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What creates most lunar craters?
High-speed impacts
Nearly every crater on the Moon was punched out by rock arriving at tens of thousands of miles an hour. With almost no atmosphere to burn up incoming debris, no rain or wind to erode the scars and no plate tectonics to recycle the crust, the surface keeps a record of impacts billions of years old.
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Which gas makes up most of Mars's atmosphere?
Carbon dioxide
Mars's thin atmosphere is about 95 percent carbon dioxide. The low pressure and cold conditions make liquid water unstable on much of the surface today.
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How long does Mercury take to complete one orbit around the Sun?
88 Earth days
Mercury circles the Sun in 88 Earth days, the shortest year of any planet. It turns on its axis once every 59 Earth days, three rotations for every two orbits, and the two motions combine so that a single sunrise-to-sunrise day on Mercury lasts about 176 Earth days, or two full Mercury years.
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What is a space rock called after it survives the atmosphere and reaches the ground?
Meteorite
Most meteorites are fragments chipped off asteroids in the asteroid belt between Mars and Jupiter, though a small number have been traced back to impacts on the Moon or Mars.
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The Moon's surface gravity is approximately what fraction of Earth's?
One-sixth
The Moon's surface gravity is about 16.5 percent of Earth's, or roughly one-sixth. Astronauts could therefore make unusually long, slow-looking jumps on the Moon.
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What is the closest star to the Sun?
Proxima Centauri
Proxima Centauri is the nearest individual star to the Sun, about 4.24 light-years away.
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On which planet is Olympus Mons located?
Mars
Olympus Mons is a huge shield volcano on Mars and is the tallest known planetary volcano in the Solar System. Its broad shape comes from repeated, low-viscosity lava flows.
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A straight line of three prominent stars is associated with which constellation?
Orion
The three aligned stars are the asterism commonly called Orion's Belt.
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Which star cluster is also known as the Seven Sisters?
The Pleiades
Only six or seven of its stars are visible to the naked eye, though the cluster holds well over a thousand in total. They formed together around 100 million years ago and are still wrapped in wisps of blue reflection nebula, visible in long exposure photos.
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In what year was Pluto reclassified as a dwarf planet?
2006
The International Astronomical Union adopted its formal planet definition in 2006, placing Pluto in the dwarf-planet category because it has not cleared its orbital neighborhood.
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Polaris, the North Star, is part of which constellation?
Ursa Minor
Polaris sits at the end of the handle of the Little Dipper, an asterism within Ursa Minor. It appears nearly fixed in the northern sky because it lies close to Earth's north celestial pole.
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Which planet is the smallest in our Solar System?
Mercury
Mercury is the smallest planet, with a diameter of about 4,880 kilometers. It is only slightly larger than Earth's Moon.
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What is the Sun's outer atmosphere called, visible during a total solar eclipse?
The corona
The corona is the Sun's outer atmosphere and becomes visible when the bright solar disk is blocked during a total eclipse.
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What alignment causes a solar eclipse?
The Moon moves between Earth and the Sun
A solar eclipse occurs when the Moon passes between Earth and the Sun and blocks some or all of the Sun’s light. A total eclipse is visible only along the narrow path where the Moon’s shadow reaches Earth.
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How many planets orbit the Sun?
8
Eight planets orbit the Sun. Pluto, once counted as the ninth, was classified as a dwarf planet in 2006.
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Which element fuels the Sun's main nuclear fusion process?
Hydrogen
In the Sun's core, at roughly 15 million degrees, hydrogen nuclei fuse into helium through the proton-proton chain. The helium that comes out weighs slightly less than the hydrogen that went in, and the missing mass leaves as energy, about four million tonnes of it every second.
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About how long does sunlight take to travel from the Sun to Earth?
About 8 minutes
Light travels from the Sun to Earth in about 8 minutes 20 seconds.
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Which zodiac constellation is traditionally associated with a bull?
Taurus
Its brightest star, the orange giant Aldebaran, marks the bull's eye, and the Hyades star cluster forms its V-shaped face. The Crab Nebula, remnant of a supernova recorded by Chinese astronomers in 1054, lies near the tip of one horn.
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What does UFO stand for?
Unidentified flying object
The US Air Force coined the term in the 1950s to replace 'flying saucer', which assumed a shape the reports did not support.
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Which atmospheric gas gives Uranus its distinctive blue-green color?
Methane
Methane absorbs much of the red light in sunlight and leaves more blue light to be reflected back into space. A small amount of a gas can therefore have a major effect on a planet's appearance.
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Which planet rotates with an extreme sideways tilt?
Uranus
Uranus has an axial tilt of about 98 degrees, so it rotates nearly on its side.
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A white dwarf usually forms from what kind of celestial object?
A Sun-like star
A white dwarf usually forms from a Sun-like star after it exhausts its nuclear fuel and sheds its outer layers. The remaining core is about the size of Earth but can contain roughly the Sun’s mass.
Medium Space Trivia Questions
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What did NASA put aboard both Voyager probes as a message to whoever might one day find them?
A gold-plated phonograph record
Each Voyager carries a gold-plated copper record of sounds, music and images from Earth, with a stylus and playing instructions. The earlier Pioneer probes carried engraved plaques instead.
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The Orion Nebula is best known as what kind of region?
A stellar nursery
The Orion Nebula is a bright star-forming cloud where new stars are still condensing out of gas and dust, which is what makes it glow.
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What do we call an object that forms like a star but is too small to sustain hydrogen fusion?
Brown dwarf
Brown dwarfs occupy the mass range between giant planets and the smallest true stars. They can glow from leftover formation heat even though they never maintain ordinary hydrogen fusion.
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What is Ceres officially classified as?
Dwarf planet
Ceres is the largest object in the main asteroid belt and the only dwarf planet located inside Neptune's orbit. It was visited by NASA's Dawn spacecraft.
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Which constellation helps southern-sky observers locate the direction of south?
Crux
Crux, also called the Southern Cross, helps observers locate south.
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The Northern Cross asterism belongs to which constellation?
Cygnus
The pattern represents a swan flying along the Milky Way, and its brightest star, Deneb, marks the swan's tail. Deneb also anchors one corner of the Summer Triangle, the seasonal shape it forms with Vega and Altair.
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What does NASA's Perseverance rover cache for possible return to Earth?
Drilled rock cores
Perseverance drills finger-sized rock cores and seals them in metal tubes, some of them left in a depot on the surface for a future mission to collect.
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By roughly how many degrees is Earth's axis tilted?
About 23.5 degrees
Earth spins on an axis tilted about 23.5 degrees from upright, which is why each hemisphere leans toward the Sun for half the year and away for the other half, giving us the seasons. Measured from the plane of Earth's orbit rather than from the upright, the same tilt reads 66.5 degrees.
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What produces most annual meteor showers?
Earth crossing a comet's debris trail
Comets shed dust along their orbits, and a shower happens each year when Earth ploughs through one of those trails at the same point in its own orbit.
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What is Earth's approximate escape velocity?
About 11 km/s
Earth's escape velocity is about 11.2 km/s. About 8 km/s is the speed needed for low Earth orbit, not escape.
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Which Soviet space station was the first to be assembled in orbit from separately launched modules?
Mir
Mir's core module launched in 1986 and further modules were flown up and docked to it over the next decade, growing the station piece by piece while crews lived aboard almost continuously until 2001. Every Salyut before it had reached orbit as a single spacecraft.
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Castor and Pollux are the brightest stars associated with which constellation?
Gemini
Castor and Pollux are the two principal stars of Gemini.
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Which probe made the first landing on Saturn's moon Titan?
Huygens
The European Space Agency's Huygens probe rode to Saturn aboard Cassini, then parachuted through Titan's haze and landed in January 2005.
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What gases make up most of the atmospheres of Uranus and Neptune?
Hydrogen and helium
Hydrogen and helium dominate the outer atmospheres, as they do for Jupiter and Saturn. Methane is present in much smaller amounts but strongly affects the planets' color.
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At approximately what speed does the International Space Station orbit Earth?
17,500 miles per hour
At that speed the station completes a full orbit roughly every 90 minutes. That works out to about 16 sunrises and sunsets for the astronauts on board each day.
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About how many sunrises do the crew of the International Space Station see in 24 hours?
16
The station laps the Earth roughly once every 90 minutes, so it crosses from night into daylight about 16 times a day. Crews keep to Greenwich Mean Time and blackout blinds to hold on to a normal sleep cycle.
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Which of Jupiter's moons is the leading target in the search for life, because of the liquid-water ocean beneath its ice?
Europa
Europa's ocean is thought to hold twice as much water as all of Earth's oceans combined, kept liquid by the tidal squeezing of Jupiter's gravity and in contact with a rocky seafloor. That combination is why NASA sent the Europa Clipper spacecraft to survey it.
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Which zodiac constellation contains the bright star Regulus?
Leo
Regulus, Alpha Leonis, is the brightest star in Leo and sits close to the ecliptic, so the Moon and planets pass near it. Leo is traditionally drawn as a lion.
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What are Mars's two natural moons called?
Phobos and Deimos
Mars has two small moons, Phobos and Deimos, named for figures from Greek mythology.
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What type of galaxy is the Milky Way?
Barred spiral
The Milky Way is a barred spiral galaxy, meaning its spiral arms extend from a central bar of stars. Our Sun is located in the Orion Spur.
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About how long is the Moon's cycle from one new moon to the next?
29.5 days
The synodic month lasts about 29.5 days. It is longer than the Moon's sidereal orbit because the Moon must catch up with Earth's changing position around the Sun.
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What keeps nearly the same side of the Moon facing Earth?
Tidal locking
Earth's gravity raised a slight bulge in the young Moon, and the drag on that bulge slowed its spin until it turned exactly once per orbit. The Moon still rotates, just in lockstep with its orbit, so the same hemisphere stays pointed at us.
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Which moon has a thick atmosphere and lakes of liquid methane?
Titan
Titan, Saturn's largest moon, is the only moon in the solar system with a dense atmosphere, mostly nitrogen and pressing harder at the surface than Earth's does. It is also the only world besides Earth with standing liquid on its surface: seas and lakes of methane and ethane, fed by rain and drained by rivers.
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What forms when a dying Sun-like star sheds its outer atmosphere?
Planetary nebula
A planetary nebula forms when a dying Sun-like star releases its outer layers into space. The exposed hot core illuminates and ionizes the gas, creating a glowing shell that typically lasts only tens of thousands of years.
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What kind of object is a pulsar?
A neutron star
Their beams sweep past Earth like a lighthouse as they spin, sometimes hundreds of times per second, which is why they show up as such precise, regular pulses. The first one was mistaken for a signal from an alien civilisation when it was discovered in 1967.
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What are Saturn's rings made primarily of?
Water ice
The rings are overwhelmingly water ice, in pieces ranging from grains of sand to lumps the size of a house. Ice reflects sunlight far better than rock does, which is why the ring system is bright enough to pick out in a small telescope.
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What does the acronym SETI stand for?
Search for Extraterrestrial Intelligence
SETI describes a family of projects that scan the sky for radio or laser signals no natural process could produce. The search began in 1960 with Frank Drake's Project Ozma, which listened in on two nearby Sun-like stars for signs of a broadcast.
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Which orbital observatory launched in 1990?
Hubble Space Telescope
Hubble went up aboard the shuttle Discovery in April 1990. Its first pictures came back blurred by a flaw ground into the primary mirror, about a fiftieth the width of a human hair, and a shuttle crew fitted corrective optics in 1993 to fix it.
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Which spacecraft made the first close flyby of Pluto?
New Horizons
New Horizons launched in January 2006 and passed about 12,500 kilometres above Pluto in July 2015, after a journey of nine and a half years. It sent back the first sharp pictures of the surface, including the vast nitrogen-ice plain now called Sputnik Planitia, then flew on to a small Kuiper Belt object in 2019.
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What is the Sun's main spectral class?
G
The Sun is a G-type main-sequence star, often written G2V. Its surface temperature gives it a yellowish-white appearance.
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Which galaxy is the nearest large spiral galaxy to the Milky Way?
The Andromeda Galaxy
Andromeda lies about 2.5 million light-years away and is closing on us. Triangulum is nearby too but far smaller, and the Large Magellanic Cloud is closer still but not a large spiral.
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How many Earth-sized worlds are known in the TRAPPIST-1 planetary system?
Seven
TRAPPIST-1 is an unusually compact system about 40 light-years away. All seven of its known planets are roughly Earth-sized, and several receive amounts of starlight that make them interesting habitability candidates.
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The Big Dipper is a well-known asterism found within which larger constellation?
Ursa Major
A line drawn through its two front stars, Dubhe and Merak, points almost directly at Polaris, the North Star, which is why the shape has long been used for navigation. Mizar, in the handle, is itself a naked-eye double, paired with the fainter star Alcor.
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What is the huge canyon system that runs along the Martian equator called?
Valles Marineris
Valles Marineris runs more than 4,000 km along Mars's equator and is up to 7 km deep, dwarfing the Grand Canyon.
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On which planet is one rotation on its axis longer than one trip around the Sun?
Venus
Venus rotates once every 243 Earth days but orbits the Sun every 225 Earth days. Its slow rotation is also retrograde, meaning it spins opposite to most planets.
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Which spacecraft was the first human-made object to enter interstellar space?
Voyager 1
NASA reports Voyager 1 crossed the heliopause into interstellar space in 2012.
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Which part of the electromagnetic spectrum does NASA's Chandra Observatory primarily observe?
X-rays
Chandra observes X-rays, which is why it sees the hottest and most violent things in the universe: black hole surroundings, exploded stars and gas between galaxies.
Hard Space Trivia Questions
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Which comet did ESA's Rosetta mission orbit?
67P/Churyumov-Gerasimenko
Rosetta spent over two years escorting the rubber-duck-shaped comet 67P/Churyumov-Gerasimenko and dropped the Philae lander onto it in 2014.
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Which type of pulsating star can serve as a standard candle?
A Cepheid variable
A Cepheid's pulsation period tracks its true brightness, so timing the pulses reveals how luminous it really is and therefore how far away it must be.
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What is the brief bright explosion associated with merging neutron stars called?
A kilonova
A kilonova is the short-lived glow from a neutron-star merger, powered by the radioactive decay of freshly forged heavy elements such as gold and platinum.
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In a classical nova, which kind of star undergoes the surface outburst?
A white dwarf
Hydrogen pulled from a companion piles up on a white dwarf until it ignites in a thermonuclear flash. The star survives, so the same system can erupt again.
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The cosmic microwave background is light released roughly how long after the Big Bang?
About 380,000 years
For its first few hundred thousand years the universe was an opaque plasma. At around 380,000 years it cooled enough for atoms to form and light to fly free, and that light is what we now detect as microwaves.
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How does the atmospheric pressure at Venus's surface compare with Earth's?
About 90 times Earth's
Venus's thick carbon-dioxide atmosphere presses down at roughly 90 Earth atmospheres, about what a submarine would feel 900 metres under the ocean.
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How much lunar rock and soil did the Apollo missions bring back to Earth in total?
About 380 kg (840 lb)
Six Apollo crews returned 382 kg (842 lb) of rock, dust and drilled cores between 1969 and 1972. A portion has never been opened, deliberately held back for instruments that had not been invented yet.
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From which asteroid did NASA's OSIRIS-REx return a sample to Earth?
Bennu
OSIRIS-REx grabbed material from the near-Earth asteroid Bennu in 2020 and dropped the sample capsule into the Utah desert in 2023. Ryugu was Japan's Hayabusa2 target.
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Brown dwarfs never ignited hydrogen fusion. Which band do astronomers use to find them?
Infrared radiation
Brown dwarfs are cool objects whose residual internal heat is most clearly detected in infrared wavelengths.
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Which supernova remnant lies in the constellation Taurus?
Crab Nebula
The Crab Nebula is the expanding wreckage of a star whose explosion was recorded by Chinese astronomers in 1054. A pulsar spinning about 30 times a second sits at its centre.
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Which constellation winds between the two bears in northern-sky star charts?
Draco
Draco is a long, faint dragon whose coils curl between Ursa Major and Ursa Minor. It is circumpolar from most of the northern hemisphere, so it never sets, and its star Thuban was the pole star at the time the Egyptian pyramids were being built.
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Which approach has found the most confirmed exoplanets?
Transit method
The transit method detects a tiny dip in a star’s brightness when a planet passes in front of it, and it has found more confirmed exoplanets than any other approach. Repeated dips can reveal the planet’s orbit and help estimate its size.
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On which planet are the fastest winds in the solar system found?
Neptune
Neptune's winds can reach roughly 1,300 miles per hour, faster than any known planetary winds. The planet's powerful weather is surprising because it receives little sunlight compared with the inner planets.
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When did continuous human occupation of the International Space Station begin?
November 2000
Expedition 1 arrived in November 2000 and began an uninterrupted human presence aboard the station. The ISS itself had begun assembly two years earlier.
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Why was the 2017 neutron-star merger GW170817 a landmark for astronomy?
It was detected in both gravitational waves and light
GW170817 was the first event seen in gravitational waves and across the electromagnetic spectrum, launching multi-messenger astronomy. The first gravitational wave detection was GW150914, two years earlier.
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What is the largest known impact feature on the Moon?
South Pole-Aitken Basin
This far-side scar measures roughly 2,500 kilometres across and up to 8 kilometres deep, formed in an impact about 4.3 billion years ago that makes it the Moon's oldest large basin. The impact left the crust here only about 30 kilometres thick, roughly half the Moon's average.
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What gives lunar maria their darker appearance than the highlands?
Iron- and magnesium-rich basalt
The lunar maria look darker because they are made of iron- and magnesium-rich basalt, which reflects less sunlight than the lighter highlands. Most maria formed when ancient volcanic lava filled large impact basins.
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The first image of a black-hole shadow showed which object?
M87*
The Event Horizon Telescope released the M87* image in 2019. The black hole at our own galaxy's centre, Sagittarius A*, was not imaged until 2022.
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Which planet has the largest core in proportion to its size?
Mercury
Mercury's iron core fills roughly 85 percent of the planet's radius, leaving only a thin rocky shell. Earth's core reaches barely half of its radius.
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What geological difference distinguishes the Moon's far side from its near side?
The far side is more cratered
The far side is almost entirely ancient highland crust, saturated with impact craters, while about a third of the near side is smooth dark maria formed by ancient lava flows. The far side's crust also runs thicker, which likely kept magma from reaching the surface there to erase those old scars.
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How long does the Moon take to orbit Earth once relative to the background stars?
27.3 days
This is called a sidereal month. The more familiar cycle from one full moon to the next, called a synodic month, runs about 29.5 days, because Earth has moved along its own orbit meanwhile and the Moon needs extra time to line back up with the Sun.
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Dark volcanic plains cover much of the Moon's near side but almost none of the far side. Why?
The near-side crust is much thinner
The Moon's crust on the near side is only about two-thirds as thick as on the far side. Molten rock from below could therefore reach the surface and flood the great impact basins there, leaving the smooth dark maria. On the thicker far side the lava mostly never got out, so its basins stayed bright and cratered.
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Neptune radiates far more energy than it receives from the Sun. Where does the extra come from?
Heat left over from the planet's formation
Neptune gives out roughly 2.6 times as much energy as it absorbs from the Sun, the largest excess of any planet. The surplus is primordial heat still leaking out of the interior, left over from the planet's formation, and it is thought to be what powers the fastest winds in the solar system at over 2,000 km/h.
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How long does a typical planetary nebula remain visible before dispersing?
About 10,000 years
The glowing shell thrown off by a dying sun-like star expands, thins and fades into the interstellar medium after roughly ten thousand years. Set against the billions of years the star spent burning, that is an instant, which is why only a few thousand planetary nebulae are visible in the galaxy at any moment.
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What phase follows core-hydrogen exhaustion in a Sun-like star?
Red giant
A Sun-like star expands into a red giant after exhausting hydrogen in its core. The other options are real later evolutionary phases or outcomes for low-mass stars.
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Who first worked out that Saturn is encircled by a ring?
Christiaan Huygens
Christiaan Huygens announced in 1655 that Saturn is girdled by a thin flat ring touching the planet nowhere. Galileo had seen something strange either side of the planet in 1610 and called them ears or handles, but his telescope could not resolve what he was looking at.
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Saturn's main rings stretch about 270,000 km across. Roughly how thick are they, top to bottom?
About 10 metres
The main rings are typically only about ten metres thick. They form a sheet of orbiting ice roughly the height of a house, spread across a quarter of a million kilometres. Set against their width, they are thousands of times thinner in proportion than a sheet of paper.
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Which zodiac constellation contains the bright star Antares?
Scorpius
Antares is the prominent red star associated with Scorpius.
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In which galaxy did Supernova 1987A occur?
Large Magellanic Cloud
The Large Magellanic Cloud is a satellite galaxy of the Milky Way about 160,000 light-years away. SN 1987A occurred in its constellation Dorado.
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Near which point in the Sun-Earth system does the James Webb Space Telescope operate?
Sun-Earth L2
Webb orbits near Sun-Earth L2, about 1.5 million km beyond Earth, where the Sun, Earth and Moon all sit on one side so a single sunshield can keep the telescope cold.
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What is the maximum-mass limit for a stable white dwarf called?
The Chandrasekhar limit
Above roughly 1.4 solar masses, electron pressure can no longer hold a white dwarf up and it collapses. The Tolman-Oppenheimer-Volkoff limit is the equivalent ceiling for neutron stars.
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What is the ISS module with large windows used for observing Earth and space called?
The Cupola
The Cupola is a seven-windowed bay added in 2010, used both for photographing Earth and for watching robotic-arm work outside.
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Astronomers measure the distance to a nearby star by parallax. What are they actually observing?
The star's tiny shift against the background as Earth orbits the Sun
Earth's viewpoint moves right across its orbit over a year, so a nearby star appears to shift slightly against far more distant stars. The size of that shift gives the distance directly.
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Enceladus jets water ice into space from four long fractures near its south pole. What are those fractures commonly called?
Tiger stripes
Cassini found four roughly parallel fractures, nicknamed tiger stripes, venting salty water from the ocean beneath the moon's ice shell.
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Why are Uranus and Neptune called ice giants rather than gas giants?
More water, methane and ammonia than hydrogen and helium
Under intense pressure, those water, methane and ammonia compounds settle into a hot, dense fluid layer around a rocky core, unlike the hydrogen and helium that dominate Jupiter and Saturn. Methane also absorbs red light, giving both planets their blue-green color.
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Who discovered Triton, the largest moon of Neptune?
William Lassell
William Lassell, a Liverpool brewer who ground his own mirrors, found Triton on 10 October 1846, just seventeen days after Neptune itself was first seen. The moon orbits backwards, which is why it is thought to be a captured object rather than one formed alongside the planet.
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