June 20, 2011

Summer Solstice 2011

Tuesday, June 21, 2011 marks the Summer Solstice.

The Summer Solstice, or "Midsummer," derived from the Latin sol (sun) and sistere (to stand still), occurs exactly when the Earth's axial tilt is most inclined towards the sun at its maximum of 23° 26'. This is the time when the Sun is at its highest, or most northerly, point in the sky in the Northern Hemisphere.

Except in the polar regions, where daylight is continuous for many months during the spring and summer, the day on which the Summer solstice occurs is the day of the year with the longest period of daylight. Thus the seasonal significance of the Summer solstice is in the reversal of the gradual shortening of nights and lengthening of days. In the Northern Hemisphere, the Summer solstice occurs in June (this year on June 21, 2011). In the Southern Hemisphere, it occurs in December.

On the day of the solstice, the Sun reaches its most Northerly point and momentarily stands still before starting its journey South in the sky until it reaches its most Southerly point -- Winter Solstice -- and then the cycle repeats.

North of the Tropic of Cancer and south of the Tropic of Capricorn the Sun reaches its highest position in the sky on the day of the summer solstice. However, between both Tropics, the highest sun position does not occur at the Summer solstice, since the Sun reaches the zenith here and it does so at different times of the year depending on the latitude of the observer. Depending on the shift of the calendar, the Summer solstice occurs sometime between June 20 and June 21 in the Northern Hemisphere, and December 21 and December 22 in the Southern Hemisphere.

It is not actually the Sun that moves North or South over the seasons, however, although it may appear that way. It is actually Earth's axial tilt that causes the Sun to change position in the sky as the Earth orbits the Sun throughout the year.

Interpretation of the solstice has varied throughout many cultures, but most have held a recognition of sign of the fertility, involving holidays, festivals, gatherings, rituals and other celebrations around the time of the solstice.

In Northern Europe the Summer solstice is most famously associated with Stonehenge, where the Sun has been worshipped for thousands of years.