This picture above shows a galaxy far out in space. At night, and using just our eyes, we can see a portion of our own galaxy (known as the Galaxy, with a capital G): we call this region the Milky Way. The whole of the Galaxy, including the region called the Milky Way, may contain several billion stars, of which our Sun is one tiny member on the outer edge of one of the spiral arms.

Set within the Galaxy are stars in many forms of their evolution. Some are new stars set far out on the spiral arms; others, nearer the centre, are up to 15 billion years old; some have even collapsed and produced the strange forms called black holes.

The size of the Galaxy

The Galaxy, like others in the Universe, is disc-shaped. The Galaxy is so big it has to be measured in light years – the distance light travels in one year. The Galaxy is 100,000 light years across and 2,000 light years thick. The Sun is over 30,000 light years from the centre of the Galaxy.

Nearby, there are 20 large galaxies that together make a cluster. The largest and most prominent of these is called the Andromeda Galaxy, more than 2 million light years away. What we see of this galaxy in the sky is, therefore, what it looked like 2 million years ago!