Galaxies
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99 free Galaxies trivia questions with answers — science & nature quiz, new questions added Oct 2026.
A galaxy is a gravitationally bound city of stars, gas, dust and dark matter, and the observable universe holds somewhere between 200 billion and two trillion of them. For most of history they were a mystery: Aristotle thought the Milky Way was burning vapour, Galileo resolved it into stars in 1610, and astronomers were still arguing in 1920 about whether the "spiral nebulae" were inside our galaxy or island universes of their own. These 99 questions cover the science and the story. You will meet the Hubble sequence of ellipticals, spirals and irregulars, the bar at the heart of the Milky Way, density waves, starbursts, radio lobes stretching millions of light-years, Seyferts, quasars and blazars. The history questions run from Democritus and Ibn al-Haytham through Lord Rosse's sketch of the Whirlpool to Vera Rubin's rotation curves and the Hubble Deep Field. The cosmology questions cover the Local Group, the Laniakea Supercluster, the Kraken merger and the collision with Andromeda due in five billion years. Easy questions stick to shapes and famous names; the expert tier asks about isophotal diameters, Petrosian magnitudes and the dark ages before the first stars. Every answer is cited and explained.
30 of 99 questions with answers and explanations. Play the quiz
Q 01In the best-known Greek myth, the Milky Way is milk spilled by which goddess as she pushed Zeus's nursing infant son away?
Hera
Hera. The baby was Heracles, and her spilled milk also gave us the word galaxy, from the Greek gala, meaning milk; the Romans carried the image over as via lactea.
Q 02What type of galaxy is the Milky Way?
Barred spiral
Barred spiral. Dust in the disc hides the core from us, so the long bar of old stars across it was only pinned down in 2005, by the Spitzer infrared telescope.
Q 03Which space telescope, launched in 2021, was built to see the universe's first galaxies in infrared light?
Webb
Webb. It works about 1.5 million kilometres from Earth behind a five-layer sunshield, because its own warmth would otherwise swamp the faint infrared glow it is hunting.
Q 04Most of the mass in a typical galaxy is in what form?
Dark matter
Dark matter. In 1933 Fritz Zwicky found the galaxies in one cluster moving far too fast for their visible matter to hold them together, and blamed something unseen that he called 'dunkle Materie'.
Q 05What is commonly found at the centre of a galaxy?
A supermassive black hole
A supermassive black hole. Astronomers showed the Milky Way has one by tracking stars as they whip around an unseen point at its centre, work that won the 2020 Nobel Prize in Physics.
Q 06A 2016 study estimated the observable universe holds at least how many galaxies?
Two trillion
Two trillion. The study concluded that about 90 percent of galaxies are too faint and too far away for even Hubble to see, which put the total at ten times the earlier estimate.
Q 07Roughly how far from Earth is the Andromeda Galaxy?
2.5 million light-years
2.5 million light-years. The light reaching your eye tonight left Andromeda long before modern humans existed, yet it is the nearest large galaxy and you can see it without a telescope.
Q 08The Milky Way belongs to which small association of galaxies?
The Local Group
The Local Group. Gravity binds its 50-plus galaxies so firmly that, while most of the universe flies apart, its two giants, the Milky Way and Andromeda, are falling toward each other.
Q 09The Milky Way's home group is part of which supercluster?
Virgo
Virgo. The supercluster is named for the great cluster at its heart, but since 2014 astronomers have treated it as just one lobe of a far larger structure, mapped by the way galaxies flow.
Q 10Before the word galaxy caught on, other galaxies were popularly called what?
Island universes
Island universes. The name pictured each spiral nebula as a separate system of stars marooned far outside the Milky Way, a claim astronomers fought over until the 1920s.
Q 11Which astronomer championed the word "galaxy" while Edwin Hubble stuck with "nebulae"?
Harlow Shapley
Harlow Shapley. He had already redrawn our place in the cosmos once, using far-off star clusters to show that the Sun sits nowhere near the centre of the Milky Way.
Q 12Which Greek philosopher explained the Milky Way as a fiery vapour burning in Earth's upper atmosphere?
Aristotle
Aristotle. He filed the Milky Way with shooting stars as a kind of fire in the upper air, and brushed aside Democritus, who held that it was the light of stars.
Q 13When two galaxies collide, why do almost none of their stars actually crash into each other?
They are too far apart
Q 21Beginning in 1912, Vesto Slipher found the light of most spiral nebulae shifted toward which colour, a sign they were racing away?
Red
Red. A few close neighbours broke the pattern, Andromeda among them: their light is shifted the other way, toward blue, because they are falling toward us.
Q 22Why do the arms of a spiral galaxy look bluer than its central bulge?
They hold young, hot stars
They hold young, hot stars. New stars form in the gas-rich arms, and the hottest, bluest of them die young, so the bulge, where star birth stopped long ago, is left with a warmer, yellowish glow.
Q 23Which variable stars let Edwin Hubble measure distances to the spiral nebulae?
Cepheids
They are too far apart. If the Milky Way and Andromeda do merge, the Sun should come through untouched but end up on a new orbit, probably much farther from the core.
Q 14Who proved in 1610 that the Milky Way is made of countless faint stars?
Galileo Galilei
Galileo Galilei. Through his new telescope the hazy band broke up into countless separate stars, and within weeks he had rushed the news into print in a booklet called the Starry Messenger.
Q 15Which German philosopher argued in 1755 that the Milky Way is one of many discs of stars?
Immanuel Kant
Immanuel Kant. He took the disc idea from a review of a book by the English astronomer Thomas Wright, then guessed that faint smudges in the sky were other Milky Ways, 170 years before anyone could prove it.
Q 16Who first mapped the Milky Way's shape in 1785 by counting stars in different directions?
William Herschel
William Herschel. Counting with his sister Caroline, he got the disc shape right but put the Sun near the hub, because dust hid all but the nearest few thousand light-years of stars.
Q 17Besides Andromeda, which spiral galaxy can keen eyes spot without a telescope under very dark skies?
Triangulum
Triangulum. Its glow is spread so thin that a little light pollution wipes it out, which is why stargazers use spotting it as a test of a truly dark sky.
Q 18The two small companion galaxies that light up southern skies are named after which explorer?
Ferdinand Magellan
Ferdinand Magellan. Neither he nor his voyage's chronicler, who described the pair around 1520, gave them the name; it spread among sailors and took centuries to reach the science books.
Q 19Charles Messier catalogued fuzzy sky objects because they kept being mistaken for what?
Comets
Comets. Messier hunted them for a living and listed the look-alikes as nuisances to skip, yet that list of things to ignore is what made his name.
Q 20In 1845 Lord Rosse used the world's largest telescope to make the first drawing of spiral arms in which galaxy?
Whirlpool
Whirlpool. Rosse sketched its spiral by hand at the eyepiece of the 72-inch giant he had built on his Irish estate, a telescope that stayed the world's largest for some seventy years.
Cepheids. The slower one of these stars pulses, the brighter it truly is, a rule found by Henrietta Leavitt, so comparing true with apparent brightness gave Hubble the distance.
Q 24Radio telescopes map the Milky Way's dust-hidden spiral arms using a famous hydrogen signal at which wavelength?
21 cm
21 cm. Radio waves of that length pass straight through the dust that blocks starlight, so the signal gave astronomers their first real map of the Milky Way's spiral arms.
Q 25Whose 1970s work on galaxy rotation speeds pointed to large amounts of unseen mass?
Vera Rubin
Vera Rubin. She found stars at the outer edge of spiral galaxies moving so fast they should fly off into space, unless far more material than anyone could see was holding them in.
Q 26Hubble's director spent ten days in 1995 staring at what?
A blank patch of sky
A blank patch of sky. Doubters had predicted Hubble would see nothing new so far out, but the tiny speck in Ursa Major came back crowded with roughly 3,000 galaxies.
Q 27Edwin Hubble's famous diagram sorting galaxies by shape is nicknamed after which everyday object?
A tuning fork
A tuning fork. Ellipticals line up along the handle, and the diagram then splits into two prongs because spirals come in two families, those with a central bar and those without.
Q 28The largest known galaxies sit where?
At a cluster's centre
At a cluster's centre. Sitting where neighbours fall in, these giant ellipticals grow by swallowing them, and many still show several bright cores, the remains of their victims.
Q 29Roughly how long does the Sun take to circle the centre of the Milky Way once?
230 million years
230 million years. One lap is called a galactic year, and it takes that long even though the Solar System is covering it at about 828,000 kilometres an hour.
Q 30A spiral galaxy with poorly defined, patchy arms is called what?
Flocculent
Flocculent. The word means woolly, a nod to arms that break up into fluffy tufts of stars instead of the long, sweeping lanes of what astronomers call a grand design spiral.