Of Equinoxes and Solstices

March 20, 2005 happened to be the Vernal Equinox, the official beginning of Spring in the northern hemisphere, and of Fall in the southern hemisphere.

~You watch/have watched/will watch a sun-rise at one or other point in your life.
~Ever stop to think or note that the sun never seems to rise from the same spot every day of the year?
~If you are blessed with a window not shaded from the sunlight, have you ever noted the rays of light falling inside creeps south as summer approaches, and creeps back north as winter arrives? Imagine a see-saw, the Sun on one side, the spot of light on your floor/wall on the other side, and your window sill as the pivot. The gentle swinging of this see-saw makes up the swing of the sun in the skies.
~An outcome of the earths rotary-axial tilt, it helps sustain the seasons on earth.

Image from Answers.com shows a representation of the earth and suns relative movements. Red line is earth's equator, yellow, the elliptic traces points on earth, where, on one day of the year, Sun is right overhead. The max northward swing of the sun reaches to the 23.27' N Parallel latitude, and happens during late June. Not so coincidentally, it is named the Tropic of Cancer. Similarly the southern swing is to the 23.27' S parallel, the Tropic of Capricorn. In this tropical zone you are lucky enough to have the sun beat down on your head on one or two days of the year and be able to observe the smallest footprint of your shadow.

Trivia Note: The Tropic of Cancer and Capricorn derive their names from the constellation of the Zodiac axis that shares its celestial position with the Sun during that time in the Celestial Sphere

The four book-end points on the image above, represent in turn, the Vernal Equinox, the Summer Solstice, the Autumnal Equinox and the Winter Solstice. Respectively, the beginning of Spring, Summer, Autumn and Winter. Ofcourse, it just flips for the Southern hemisphere. Usually occuring in turn, on March 20/21, June 20/21/22, September 22/23, and December 21/22.

In terms of the see-saw, the lowest swing of the Sun is the Winter Solstice, the leveling of the swing on the way up is Vernal Equinox, the highest swing is the Summer solstice, and the leveling on the way down is Autumnal Equinox.