This year Summer begins on June 21 at 11:28 am. At that time we will be farthest from the sun for the year, but because of the Earth's tilt the Sun's rays will be shining most on the Northern Hemisphere, making this the longest day of the year The Sun will reach its northern most in the sky.

Scientists have their precise instuments and have determined the time and day of each Summer Solstice; it's not always June 21. In 2012 for example the Summer Solstice will be on June 20.

In ancient times every seasons' start was a holiday and important to determining various events, such as planting and harvesting crops. At Stonehedge in Great Britain the sun rises and reflects on a specific marker at dawn this day. In some cultures this Solstice is called Midsummer (as in Shakespeare's "Midsummer's Night Dream").

At the Arctic Circle the sun seems, on this day to circle the horizon all day long. There is a six week period where there is light all day long (though the Sun will occasionally dip below the horizon its rays will still make the land seem bright. My wife and I witnessed this when we were in St. Petersburg in 2004.

However you celebrate the end of Spring and the start of Summer enjoy it while you can: the days start getting shorter on June 22.