Hat tip to DmAa on the "Bear Stories" thread at Siliconinvestor.com
Notice I said that day and night will be approximately equal on the fall equinox. The equinox is a specific point in time when the sun is at a specific point in the sky. Since sunrise and sunset times vary greatly across the planet depending on location, true equality of day and night -- called the equilux (EE-qwill-lux) -- occurs on slightly different dates depending on where you live. Equilux for Duluth, Minn. is on September 25 when the sun rises at 7 a.m. and sets at 7 p.m. To find your equilux date, go to the U.S. Naval Observatory website http://aa.usno.navy.mil/data/docs/RS_OneDay.php and type in your location to get the day's sunrise/sunset information. Are there exactly twelve hours separating them? If not, then go back, change the date a couple days ahead (or back) and look again. You may have to do this a couple times to find out when they're equal.
"http://aa.usno.navy.mil/data/docs/RS_OneDay.php"
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