Day, night and the year

The Earth spins on its axis, an imaginary line through the North and South Poles. One full spin takes 24 hours, which is one day. The half of the Earth facing the Sun has day, and the half facing away has night. As the Earth turns, the Sun seems to move across the sky, but it is really us who are moving.

The Earth also travels round the Sun, taking about 365 days, or one year. Because the Earth's axis is tilted, different parts get more direct sunlight at different times of year, which causes the seasons. Some stars can only be seen at certain times of year, because the night side of the Earth faces a different part of space.