Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!

Home > Science > The environment, the Earth and the universe > Astronomy and space science


Astronomy and space science


Days and nights

The planets spin as they orbit the Sun. It takes the Earth 24 hours to make one complete turn on its axis, so an Earth day is 24 hours long.

Different planets take different amounts of time to make one complete turn, so they have different lengths of day.

Day and night

Shows how the sun lights one side of the Earth and the other is in shadow

The Sun lights up one half of the Earth, and the other half is in shadow. As the Earth spins we move from shadow to light and back to shadow and so on. It is daytime in the UK when our part of the planet is in the lit by the Sun. And it is night-time in the UK when our part of the planet is facing away from the Sun.

Path of the Sun

During the day, the Sun appears to move through the sky. Remember that this happens because the Earth is spinning on its axis. In the UK if we look south and follow the path of Sun in the sky during the day, it looks like this:

The sun rises in the east. At midday, the sun is in the middle of the sky. The sun sets in the west

The sun rises in the east and sets in the west

The Sun appears to move from east to west. That's because the Earth is spinning towards to the east, so we see the Sun first appear there at the start of the day. The Sun 'rises' in the east and 'sets' in the west.

One way to remember which way the Earth turns is to remember "w.e. spin", which means the Earth spins from west to east.


Star trails, which form a circlular pattern in the sky, created by leaving a camera shutter open throughout the night to record the light from stars.

Star trails made by leaving the camera shutter open during the night

During the night, we cannot see the Sun. But the Earth is still spinning on its axis. This means that the stars appear to move from east to west in the sky, just as the Sun does in the day.


Astronomy and space science activity

Try an activity that's out of this world!



Can you conquer the elements?

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.