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The Day (and Night) of Solar Equality
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Tonight we mark the first official moments of fall. Starting Sunday night at precisely 9:56 the leaves will begin to turn colors and fall from the trees. The weather will become suddenly cool and windy. Football games will break out spontaneously in neighborhood parks. Christmas decorations will be out for sale at stores everywhere.
Of course we know that's not what happens when it becomes fall --- except for maybe the Christmas decoration thing. The beginning of fall for most of us passes as just a formality of the calendar and few know why we mark that day in the first place.
There was a time for humans --- and still is for some peoples of this planet --- that this event, the fall equinox, marked the special midpoint between the solstices.
The summer solstice for Northern Hemispherical people was celebrated around June 21. It was when the sun, that great bright ball in the heavens, that mysterious source of light and heat and growth, trekked across the sky on its highest path. It rose northeast on the horizon and set in the northwest. The daytime was the longest of the year; nighttime was at its shortest. Light ruled!
Six months later, around December 21, came the day the sun rose very south of east, barely cut a path much above the horizon during this "shortest day," and then just hours later set in the very southwest. Darkness was king on winter solstice.
Fall equinox, however, was the moderate diem between the two extremes. The sun rose due east, was in the sky for 12 hours --- exactly half the day --- and then set due west. The fact that the sun was up as long as it was down gave us the term equinox, which means "equal night."
People who took the equinox seriously noticed that after this day the sun would be below the horizon longer than above it. Darkness would slowly snuff out the light, until finally the winter solstice came and light would again start to fight its way back to daily supremacy. Spring would not be far off.
There really is an astronomical reason for all this. But fair warning! As usual, the cold steel of science has a way of demythologizing the more poetic and agrarian meanings of the day. Ready?
Our planet has been blessed with a tilt. And therein lies the reason for why the equinox exists. Right now we are tilted over about 23.5 degrees. But tilted compared to what? Not the sun!
Imagine the Earth orbiting around the sun. It draws out a huge near-circular path. This whole path etches out a giant circular plane.
It's like a CD (or vinyl record if you remember those). Imagine a piece of corn stuck in the middle hole. That would be our sun. (Just go with it.) The whole CD is our "orbital plane" a.k.a. the ecliptic. Our planet would be a piece of dust traveling around in a circle on the CD.
We are tilted over a little with respect to this plane. Our poles do not stand straight up at attention, perpendicular to the plane. Our north pole seems to have a mind of its own and points --- all year long --- towards a distant star called Polaris, our North Star.
Sometimes during the year --- specifically during our summer --- we just happen to be tilted toward the sun. And six months later, on the other side of the sun, we are tilted away, during the darker days of winter.
The equinoxes are between those places, where, even as our North Pole is still pining for the North Star, we are not tilted at all with respect to our own star, the sun. The sun will shine on that day from pole to shining pole, hovering directly over our equator, favoring neither hemisphere.
The whole globe during this special day has a twelve-hour day and a twelve-hour night. For every nonpolar person the sun rises due east and sets due west. It's like a Global Solar Equality Day.
Alas! It is only on that day we are all equal. The next day sees the sun rising ever so much later and setting a wee bit sooner. It travels a slightly lower path each day as we move around towards the winter part of our orbit. The shorter days make it progressively cooler. Leaves really do start to change color as trees prepare for winter.
But the beauty of it is that this marvelous cycle just keeps going year after year, giving us season after season. Every year is blessedly the same, every year wonderfully different.
Have a question or comment? Write Mark Ritter here.
Posted by Administrator at 2002.09.21 02:30 PM | Comments (0)
