Galaxies

Clusters of stars

Observations show that the stars are not uniformly distributed across the night sky, but are clustered in large collections which are called galaxies. Each cluster contains anything from 1 million to millions of millions of stars. It has long been known that our own star, the Sun, belongs to one such galaxy, but it was only in 1925 that it was realised that the universe consists of millions of galaxies. This discovery was made possible by the building of the 200 inch telescope at Mount Palomar in California.

Turning this telescope to look at what, until then, had been thought to be nebulae (the mass of gas and dust left behind as the remnants of a supernova explosion) Edwin Hubble realised that they were, in fact, individual stars. These so called nebulae were galaxies in their own right. Overnight the known universe had become a much, much bigger place.

The Sun is just one of 200 000 million stars that form our galaxy, which is called the Milky Way. The Milky Way looks like a couple of fried eggs placed together with one upside down.

From the Earth, you can see a band of stars, about 5 degrees across, right across the night sky, where there are many more stars than elsewhere. This is the view we get of the Milky Way, looking into the disc of our galaxy.