When astronomers first began using their telescopes to look at the stars, they noticed that some were more than just points of light.
Stars such as Alpha Centaurus appear as two stars close orbiting each other and are called binary stars. Castor, in the constellation Gemini, is a double binary system – two stars that orbit each other, orbiting another two stars that orbit each other.
When there are many stars grouped together they are known as a star cluster. One of the most famous clusters of stars is the Pleiades, or Seven Sisters. Using only our eyes it is possible to count six or seven stars close together. If you look through binoculars or a telescope, you should be able to count many more. Because you can easily see the gaps between them, this cluster of stars is called an open cluster.
Another type of star cluster is a globular cluster. These consist of millions of stars that appear very close together. They are so close that it’s almost impossible to pick out each individual star. Astronomers estimate that these clusters of stars may have been the centre of ancient galaxies. Two of the most famous globular clusters are 47 Tucanae and Omega Centauri.
See if you can find these star clusters using the maps below next time you look at the sky with binoculars or a telescope.