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
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-time in the UK when our part of the planet is facing away from the…