Field guide · Deep sky
GalaxyGalaxy
An island of billions of stars. Every star you can see is in ours, the Milky Way; the light of the others set out hundreds of thousands to billions of years ago.
- Stars
- Millions to trillions
- Nearest big one
- Andromeda, 2.5 million light-years
- Seen as
- A faint, soft glow
- Best seen with
- Dark skies; averted vision
Until 1924 nobody knew whether the “spiral nebulae” were small clouds inside our galaxy or other galaxies altogether. Then Edwin Hubble found a pulsating variable star in the Andromeda Galaxy, used it to measure the distance, and the universe got a great deal larger.
Galaxies come as spirals like our own, as featureless ellipticals, and as irregular shreds like the Magellanic Clouds. They gather in groups and clusters: the Milky Way and Andromeda are the two big members of the Local Group, and they are falling towards each other.
Through a telescope most galaxies are faint grey smudges, but the smudge is the combined light of hundreds of billions of suns, and it set out millions of years ago. You are looking at the past.
See it in the sky
Each one opens the sky map pointed at it, for tonight, from where you are.
- Galaxy Andromeda Galaxy Andromeda, the farthest thing most people can see by eye.
- Galaxy Large Magellanic Cloud The Large Magellanic Cloud, a satellite of the Milky Way.
- Galaxy Whirlpool Galaxy The Whirlpool, where spiral arms were first seen, in 1845.
- Galaxy Sombrero Galaxy The Sombrero, edge-on with a dark lane of dust.