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50 free Galaxies trivia questions with answers — science & nature quiz, new questions added Aug 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 50 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 50 questions with answers and explanations. Play the quiz
Q 01The word galaxy comes from a Greek word meaning what?
Milky
It referred to the pale band of our own galaxy across the night sky.
Q 02What type of galaxy is the Milky Way?
Barred spiral
A bar of stars runs through its core and merges into the spiral arms.
Q 03What are the three main types of galaxy?
Elliptical, spiral and irregular
The Hubble sequence refines these by shape.
Q 04Most of the mass in a typical galaxy is in what form?
Dark matter
Only a few percent is visible as stars and nebulae.
Q 05What is commonly found at the centre of a galaxy?
A supermassive black hole
Its existence in galactic cores was confirmed through X-ray astronomy.
Q 06A 2016 study estimated the observable universe holds at least how many galaxies?
Two trillion
That was ten times more than are directly seen in Hubble images.
Q 07Roughly how far away is the Andromeda Galaxy?
2.4 million light-years
It is the Milky Way's nearest large neighbour.
Q 08The Milky Way belongs to which small association of galaxies?
The Local Group
It dominates the group together with Andromeda.
Q 09The Milky Way's home group is part of which supercluster?
Virgo
That supercluster is itself a portion of the larger Laniakea Supercluster.
Q 10Before their nature was understood, galaxies were popularly called what?
Island universes
Astronomers also called them spiral nebulae.
Q 11Which astronomer championed the word "galaxy" while Edwin Hubble stuck with "nebulae"?
Harlow Shapley
The nomenclature only fully changed after Hubble's death in 1953.
Q 12Which Greek philosopher proposed that the Milky Way might be made of distant stars?
Democritus
Aristotle instead thought it was burning vapour in the upper atmosphere.
Q 13Which astronomer first tried to measure the Milky Way's parallax and concluded it was remote?
Ibn al-Haytham
No parallax meant it could not be part of the atmosphere.
Who proved in 1610 that the Milky Way is made of countless faint stars?
Q 21Who discovered in 1912 that spiral nebulae showed large Doppler shifts, mostly moving away?
Vesto Slipher
His spectrographic work predated Hubble's distance measurements.
Q 22In which year did the "Great Debate" over the nature of spiral nebulae take place?
1920
Harlow Shapley argued against Heber Curtis's island-universe view.
Q 23Which variable stars let Edwin Hubble measure distances to the spiral nebulae?
Cepheids
He used the 100-inch telescope on Mount Wilson.
Q 24Hendrik van de Hulst predicted in 1944 that interstellar hydrogen would emit at which wavelength?
Galileo Galilei
He turned his new telescope on the pale band and resolved it.
Q 15In 1750 who speculated that the Milky Way was a flattened, rotating disk of stars?
Thomas Wright
Kant elaborated on his idea five years later.
Q 16Who first mapped the Milky Way's shape in 1785 by counting stars in different directions?
William Herschel
His diagram wrongly put the Solar System near the centre.
Q 17Which of these galaxies can be seen with the naked eye on a dark night?
Triangulum
Andromeda and the two Magellanic Clouds are the others.
Q 18Which 10th-century Persian astronomer described Andromeda as a "small cloud"?
Abd al-Rahman al-Sufi
His Book of Fixed Stars may also mention the Large Magellanic Cloud.
Q 19How many nebulous objects did Charles Messier's 18th-century catalogue list?
109
Herschel later assembled a catalogue of 5,000 nebulae.
Q 20Who first observed spiral structure in a nebula, M51, in 1845?
Lord Rosse
M51 is now known as the Whirlpool.
21 cm
It was observed in 1951 and is unaffected by dust.
Q 25Whose 1970s work on galaxy rotation speeds pointed to large amounts of unseen mass?
Vera Rubin
The galaxy rotation problem is now explained by dark matter.
Q 26The Hubble Deep Field suggested about how many galaxies in the observable universe?
125 billion
It was a very long exposure of a nearly empty patch of sky.
Q 27In the Hubble scheme, an E7 elliptical galaxy is what?
Highly elongated
E0 is the nearly spherical end of the scale.
Q 28The largest and most luminous galaxies known belong to which class?
Type-cD
These supergiant ellipticals have faint halos stretching for megaparsecs.
Q 29About what fraction of elliptical galaxies have a shell-like halo structure?
One-tenth
NGC 3923 has more than 20 shells; the structure never appears in spirals.
Q 30A spiral galaxy with poorly defined, patchy arms is called what?
Flocculent
Grand design spirals have prominent, well-defined arms.