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Friday, September 22, 2006

Autumn Arrives

Summer is fading. The days are getting shorter and the weather cooler. Crops are being harvested and birds are getting ready to migrate south. In the Northern half of the earth winter is coming. Meanwhile, in the Southern half of the earth the days are getting shorter and the weather warmer. Farmers are getting ready to plant and birds will soon be arriving from the north. In New England and other parts of the country the countryside is about to burst into color as leaves change from their summer green to the reds, yellows and oranges of Fall providing a spectacular end to summer.

As the earth continues its never ending journey around the sun, the twenty-three plus degree tilt of its axis causes it to appear that the sun, over the course of the year, moves from north to south and vice versa. During half of the year the sun's rays are concentrated more on the Northern Hemisphere than the Southern Hemisphere and then it reverses and shines more on the Southern than the Northern Hemisphere. It is this apparent movement of the sun from north to south and back which gives us our ever changing seasons. It is also how we determine the official change from one season to another.

As I write this, a transition is about to take place. Later today the sun will be passing over the Earth's Equator and giving us one of the two days each year in which night and day are approximately equal. These two days are the known as the Equinox which is Latin for equal. In the days before the Internet the Equinox had the same name for both the writer and his audience. If I were writing this for the local newspaper I would simply state that the Autumnal (from the Latin word autumnus which means autumn), or Autumn, Equinox will be occurring tomorrow, September 22, 2006 and the season of Autumn or Fall as we North Americans tend to call it, will officially begin. However, for those in the Southern Hemisphere, it will be the Vernal (from the Latin word ver which means spring) or Spring Equinox and will signal the official start of Spring in that part of the world. The same is true for the date of the first day of Autumn/Spring. Here in western United States the sun will officially cross the Equator at 9:03 p.m. on Friday September 22, 2006. However, on the East Coast of the United States this event will occur at 12:03 a.m. on Saturday September 23, 2006. Therefore, in the western half of the world the equinox will occur on September 22nd while in the eastern half of the world the equinox will occur at the same time but, according to their clocks, it will be Saturday September 23, 2006. Meanwhile, for the southern half of the world the equinox will be the Vernal or Spring Equinox heralding the start of Spring while in the northern half of the world the event will be the Autumnal or Autumn Equinox heralding the start of Autumn.

This exercise will be repeated on March 20th or 21st of 2007 (date varies depending upon geographic location), except on that date it will be the Spring Equinox and the start of spring for the Northern Hemisphere and the Autumn Equinox and the start of Autumn for the Southern Hemisphere.

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