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Movement of the stars during 24 hours

If we observe the stars during the course of one night they seem to rise in the east, move across the sky and set in the west. If we look at the sky again the following night at the same time then the stars will have returned to more or less the same position as they were the night before.

The first diagram shows how the constellation of Orion moves during part of a winter’s night when seen from the Northern Hemisphere looking south.

Some stars never set – these are called circumpolar stars and the constellations which they are in are called circumpolar constellations. The constellation Ursa Major (the Plough) is a circumpolar constellation. You can always see it (from the Northern Hemisphere).

You can see how the Plough appears to move from one day to the next in Figure 2.

Remember that the stars are not really moving. It is the rotation of the Earth from west to east that makes them look as if they are travelling from east to west during the night.

schoolphysics: Movementof the Plough animation

To see an animation of the movement of the Plough (Ursa Major) click on the animation link.

© Keith Gibbs