Groups of stars that make patterns in certain part of the sky are known as constellations. Some of them were named by the Greeks 2000 years ago, and Arab and Chinese astronomers had their own constellations too. There are 88 constellations and they cover the whole sky. They were probably invented as a way of referring to particular stars. Although the stars in a constellations appear to us to be in group, they are really vast distances away from each other.