The fixed stars
To the Ancient Greeks the stars appeared to stay in unchanging patterns in the sky. Some particular patterns of stars have their own names – like Andromeda, Cassiopeia, Orion and the Plough. They are called constellations.
The Ancient Greeks learned some of their stories about these patterns from people before them, other myths about gods creating and swallowing stars developed over time. The patterns do not change from one millennium to the next.
But with better detection equipment we can see that the stars are not quite fixed. Some seem to wobble very slowly – once a year as the Earth goes round the Sun. This small wobble happens for stars that are closer to us. The ‘wobble’ is a parallax effect, and it happens because the Earth is moving.
Other stars do move very slowly, but it takes the best instruments making observations over a long time to be able to detect this motion.
You can find out more about Ancient Greek stories associated with the constellations here and more about Chinese constellation names
The Islamic astronomers