There are actually two different reasons why stars appear to move across our sky. The first is because the Earth is spinning and second

because the Earth itself is moving around the Sun.

What they are

• As the Earth spins around, the stars appear to move from east to west across the sky. If a long exposure camera is left facing the sky, there will be trails of light across the photograph, known as star trails.

Star images produced by a camera lens are point sources of light of widely varying intensity scattered over the film. Normally, no single photographic exposure on colour film can capture their subtle colours. Those stars whose intensity is just right for their colour to be recorded appear insignificant on the photograph, while anything brighter is bigger, but is overexposed and appears washed out.

Star trails around the celestial poles

As the Earth travels around the sun (once a year), it is as if we are sitting on a Waltzer ride at the funfair. If the whole Waltzer moved around on its track with the cars not spinning, we would see everything around the ride appear to be sweeping past once with every revolution.  Standing on the surface of Earth, as it makes its journey around the Sun we see the stars passing by until after a whole revolution around the Sun, taking a year, we will have seen all the stars pass by.

If the waltzer had no roof, the sky overhead would appear to be spinning around a point directly above the car. This area of sky would always be visible to us no matter where the car was on the track. This is the same for the stars around the north star Polaris. Because Polaris is close to the point in the sky directly above the axis of spin of the Earth (the north pole) it is always visible. The stars within 40 degrees of Polaris appear to rotate around it and do not set below the horizon, these stars are said to be ‘circumpolar’. Stars further than 40 degrees from Polaris disappear below the horizon for part of the year and reappear at the same time every year.