Originally Posted by
Musicology
Kevinthediltz,
Interesting question. Really. The seasonal changes are caused by the spiral revolutions of the Sun as it circumnavigates the Earth each day. Each orbit being different. Completing one complete cycle of revolutions each year.
Equinoxes, solstices, and tropics are the result of the north-south motion of the sun, starting with the vernal or spring equinox on March 21, the official beginning of spring in the northern hemisphere.
On that day, the sun lies on the celestial equator. The word equinox refers to the fact that, on this day, the night is equal to the day: each is twelve hours long. The sun is directly above the equator, so its rays fall vertically down.
Through the months of March, April, and May, the sun moves north. On June 22nd, it reaches its most northerly point, that is, 23 1/2° above the equator. In the northern hemisphere that day is called the summer solstice. It is the longest day of the year and the official beginning of summer. The sun lies on the circle of the earth called the Tropic of Cancer.
On September 23, the sun, moving south, reaches the equator again. The day is again 12 hours long. That day is called the autumnal equinox and is the official beginning of autumn.
On December 22, the sun reaches its most southerly point. That day is of course called the winter solstice and is the official beginning of winter. The sun shines up from beneath the equator. At noon the sun is straight overhead at points on the earth's Tropic of Capricorn, located 23 1/2° south of the equator. At that time, it is the summer solstice in the southern hemisphere. The cycle again repeats itself and gives us our 4 seasons and the solar year.
The winter solstice occurs on June 22 in the southern hemisphere. 3 days later it is June 25 or "Christmas" day in the southern hemisphere. So that the cycle begins again with the New Year starting there, in the extreme southern hemisphere.
Regards
