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Galaxies

A galaxy is what you get when gravity gathers stars — anything from a few thousand to a few hundred billion or more — into one turning system and keeps them there. There are hundreds of billions of them. On a dark autumn night you can find one of them with no equipment at all.

What a galaxy is

Stars are not scattered evenly through the universe. They come in enormous clumps, held together by gravity, with almost entirely empty space between the clumps. One clump is a galaxy. Ours is called the Milky Way, and it is an ordinary one — big, but nothing special.

🌌 Our own galaxy, in detail

The kinds there are

They come in a handful of shapes, and the shape tells you the history. Spirals are still making new stars in their arms. Ellipticals have run out of the gas to make new ones, and are coasting on the old ones. Irregulars have often been pulled out of shape by a neighbour — and some have been through an actual collision.

The Sagittarius Dwarf Galaxy and Streamdwarf galaxyBeyond a 150 mm telescopeThe Andromeda Galaxy (M31)spiral galaxyNaked eyeThe Triangulum Galaxy (M33)spiral galaxyBinocularsThe Large Magellanic Cloudirregular galaxyNaked eyeBode’s Galaxy (M81)spiral galaxyBinocularsThe Whirlpool Galaxy (M51)spiral galaxy150 mm telescopeThe Sombrero Galaxy (M104)spiral galaxyBinocularsThe Pinwheel Galaxy (M101)spiral galaxy150 mm telescopeCentaurus A (NGC 5128)elliptical galaxyBinocularsM87 / Virgo Aelliptical galaxy150 mm telescopeThe Cigar Galaxy (M82)starburst galaxyBinocularsThe Antennae Galaxies (NGC 4038/4039)colliding galaxies150 mm telescopeThe Cartwheel Galaxyring galaxyBeyond a 150 mm telescopeHoag’s Objectring galaxyBeyond a 150 mm telescopeMalin 1spiral galaxyBeyond a 150 mm telescopeThe Fireworks Galaxy (NGC 6946)spiral galaxy150 mm telescopeNGC 4993elliptical galaxyBeyond a 150 mm telescope

The ones you can actually see

Andromeda is about the far end of your own eyesight: on a moonless autumn night, with a clear view to the east (from the northern hemisphere), it is a faint smudge to the naked eye. That smudge is about 2.5 million light-years away, which means the light entering your eye left before there were any people like us.

The Andromeda Galaxy (M31)spiral galaxyNaked eyeThe Triangulum Galaxy (M33)spiral galaxyBinocularsThe Large Magellanic Cloudirregular galaxyNaked eyeBode’s Galaxy (M81)spiral galaxyBinocularsThe Sombrero Galaxy (M104)spiral galaxyBinocularsCentaurus A (NGC 5128)elliptical galaxyBinocularsThe Cigar Galaxy (M82)starburst galaxyBinoculars

Expect a smudge. Almost every galaxy photo you have seen took hours of exposure, usually on a telescope far bigger than yours. Through a small one, a galaxy is a pale grey oval with no colour and, usually, no visible arms. Knowing that in advance is the difference between a good first look and a disappointing one.

🔭 Where is Andromeda tonight?

How far away are they?

Far enough that the question was genuinely open until about a hundred years ago — people argued about whether these smudges were inside our own galaxy or were galaxies themselves. The answer came from a particular kind of star that pulses at a rate which gives away how bright it really is.

🌙 Plan an evening outsideEvery object, one by one