Seasons

1 = 2004 Mar 20 9:00:00 pm UT
2 = 2003 Jun 21 9:00:00 pm UT
3 = 2004 Sept 22 9:00:00 pm UT
4 = 2003 Dec 22 9:00:00 pm UT


Seasons Natural divisions of the year, marked by regular changes in the weather and the lengths of the days and nights. The rhythm of the seasons is most evident in temperate regions,where the four seasons : spring - summer - autumn - winter , are most distinct.

The seasons are caused by the inclination (23½°) of the earth's axis to the plane of its orbit around the Sun. This allows a certain point on the earth to receive more solar radiation at some times than at others. It is summer in the northern hemisphere ( winter in the southern) when the north pole is tilted towards (south pole away from) the Sun ; and winter in the northern hemisphere (summer in the southern) when the north pole is tilted away (south pole towards) the Sun. At times in between, when the Earth's axis is tilted nether towards nor away from the Sun, the equinoxes occur. Then day and night are of equal length throughout the worlds.

Equinoxes The two tomes of the year when day and and night are of equal length throughout the worlds. They occur when the Sun lies exactly above the equator, in the spring (spring or vernal equinox) on about March 21 as the Sun is moving north; and in the autumn (autumnal equinox) on about September 23 as the Sun is moving south.

Solstices The times in the year when the Earth's axis is tilted most towards or away from the Sun; or from an observer's point of view, the times when the sun is highest and lowest in the sky at noon. In the northern hemisphere the Sun is highest in the moon sky on about June 21 each year (summer solstice); and lowest on about December 21 (winter solstice). On these dates occur, respectively, the longest and shortest periods of daylight.