The longest day of the year, the Summer solstice, is on or near 21 June. It is the day when the sun is at its most northerly point and this is why it is "the longest day".
On this day you can see a very old custom at Stonehenge, in Wiltshire, England.
Stonehenge is one of Europe's biggest stone circles. A lot of stones are ten or twelve metres high. The earliest part of Stonehenge is nearly 5,000 years old. It is thought that the Druids used Stonehenge for a calendar.
The Druids were the priests in Britain 2,000 years ago. They used the sun and the stones at Stonehenge to know the start of the months and seasons. There are Druids in Britain today too.
Every June 21st hundreds of people go to Stonehenge to watch the sun rise. The sun shines on one famous stone - the Heel stone. For the Druids this is a very important moment of the year.
Druid celebrations also take place on Midsummer's Eve. Bonfires are lit to show respect for the Sun God, whose power is greatest at the Summer Solstice. The fires also represent an attempt to ward off the coming winter. Practice of this ancient ritual, which also includes a Summer Solstice Circle Dance, is now mainly confined to Cornwall, the West Country, and London's Hampstead Heath.
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