An equinox is an exact point in time. This Vernal, or Spring, Equinox is at 5:14 a.m. March 20th. It is the moment that the earth’s axis is tipped neither toward, nor away, from the sun. Equinox means equal night in Latin, or twelve hours of day or night. This is actually a misnomer as an exact point in time can hardly be an entire day.
The day that the equinox happens is called an equilux. However, for various reasons the length of the equilux day is actually not equal to the length of the night on that exact date. One of those reasons deals with the bending of light rays coming from the sun by earth’s atmosphere. Another is that the sun is a huge object. The twelve hour day and/or night would have to start when the sun was at its mid-point on the horizon. However daybreak happens when we first see the top of the sun on the horizon in the morning, and sunset is when we last see the top of the sun on the horizon in the evening. Thus we have one diameter of the sun in addition to our twelve hour equilux day. Actually, March 20, 2012, the Vernal Equinox, the day will be 12 hours and 9 minutes long, stretching from 7:03 in the morning to 7:12 in the evening in the northern states. In the Carolinas the sun will rise a minute later, but set at the same time.
Due to the forgoing reasons the day closest to having an equal day and night will be Friday, March 17th this spring. As we all know, March 17th is St. Patricks’s day, and so it be, Laddies and Lassies, that we shall all be wearing of the green when day and night equalize.
The shortest day of the year is the Winter Solstice which falls on December 21st, while the longest will be June 20th, the Summer Solstice.
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