A planet spins on its axis as it orbits the Sun. A day is the time it takes for a planet to turn once on its axis. An Earth day is 24 hours long.
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 lit by the Sun. And it is night in the UK when our part of the planet is facing away from 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 the Sun in the sky during the day, it looks like this:
The Sun appears to move from east to west. This is because the Earth turns from west to east. The Sun appears to:
One way to remember which way the Earth turns is to remember ‘we spin’, which means that we (the Earth) spins from west to east.
The length of the day (the time when the Sun shines on a particular part of the world) changes during the year, unless you are on the equator. Everywhere else, daytime is longest in the summer and shortest in the winter. In winter, the Sun still appears to rise in the east and set in the west, but it does not climb so high in the sky as it does in the summer.