Astronomy and space science - Years and seasons
Years
A planet's year is the time it takes to make one complete orbit around the Sun. The Earth goes once round the Sun in one Earth year. That's 365 Earth days.
We've seen already that that different planets take different lengths of time to orbit the Sun. That means their years are different lengths. Mercury has a year of just 88 Earth days, and Neptune has a year of 164 Earth years.
Seasons
The Earth's axis is the imaginary line through the centre of the Earth between the South and North poles. This axis is tilted slightly compared to the way the Earth orbits the Sun.
We get different seasons (winter, spring, summer and autumn) because the Earth is tilted. This is how it works:
When the northern hemisphere is tilted towards the Sun it is summer in the UK.
When the northern hemisphere is tilted away from the Sun it is winter in the UK.
When it is summer in the northern hemisphere, it is winter in the southern hemisphere.
Because of the tilt of the Earth's axis the Sun moves higher in the sky in summer, when we tilt towards it, than in winter.
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