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The summer solstice is the longest day of the year - that means it has the most hours of sunlight.

In the northern hemisphere (where the UK is) in 2021 it falls on Tuesday 21 June.

The summer solstice marks the end of spring and start of summer.

It will end with the autumn equinox, which last year fell on 22 September.

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This handy diagram can help you to get your head around all the astronomical seasons

We get the most hours of daylight on this day because of the position of the Earth in relation to the Sun.

It occurs when the Earth's geographical pole - on either the northern or southern hemisphere - becomes most inclined towards the Sun.

When the summer solstice takes place in the northern hemisphere, the Sun will reach its highest possible point.

As a result, the day on which the summer solstice falls will have the longest period of daylight of the year.

Our planet does not spin on a vertical axis - it is titled. This means the amount of sunlight that reaches different regions of the Earth changes during the year as it orbits the Sun.

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This is midnight on the Summer solstice 2018 in a bay in the Åland Islands, archipelago between Finland and Sweden

Around the time of the summer solstice areas of Norway, Finland, Greenland, Alaska and other polar regions experience 'midnight sun'.

In the Arctic Circle, the Sun does not set at all!

Again it comes down to the tilt of the Earth's axis.

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Summer solstice is celebrated by thousands of pagans across the world.

Many gather at Stonehenge which is believed to have been used as an important religious site by early Britons 4,000 years ago.

On the summer solstice, the central Altar stone at Stonehenge aligns with the Heel stone, the Slaughter stone and the rising Sun to the north east.