The summer solstice this year falls on Thursday June 21 in the Northern Hemisphere and is the day with the longest period of daylight.
In contrast the winter solstice is on or around December 21 in the Northern Hemisphere and is the day with the shortest period of daylight.
During the summer solstice the Northern Hemisphere of Earth is titled towards the Sun resulting in increased sunlight and warmer temperatures.
This can result in continuous daylight in far northern countries such as Iceland and Norway.
This year the summer solstice will take place on June 21 and is the longest day of the year.
When the summer solstice is over, the days start drawing in and becoming shorter.
Stonehenge is an ancient world heritage site and has been a place of worship and celebration at the time of Summer Solstice for thousands of years.
At Stonehenge, the sun will rise at 4.52am and set at 9.27pm on Thursday.
In the build up to the summer solstice we gain minutes of daylight each day and directly after the solstice we start losing seconds and then minutes of daylight until the winter solstice and the pattern reverses.
For astrologists, the summer solstice marks the beginning of summer and represents the time at which the Sun reaches its highest point in the sky in the Northern Hemisphere.
At the summer solstice the sun reaches its highest point of the year, while at the winter solstice, the noon sun is the lowest it will be all year.
The solstice does not always fall on June 21 but falls within the same three day period between June 20 and June 22.
How long is the longest day?
The summer solstice is the longest day of the year – the sun rises at 4.43am and sets at 9.21pm in the evening.
This equates to Britain enjoying 17 hours and 38 minutes of sunshine on June 21.
The June solstice is the exact instant of time when the sun is directly overhead the Tropic of Cancer.
In 2018, this will happen at 11.07am BST (10.07am UTC).