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What's an Equinox? |
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Adapted from entries in the Wikipedia In astronomy, an equinox is defined as the moment when the sun reaches one of two intersections between the ecliptic and the celestial equator. The word equinox comes from the Latin for equal night. The equinoxes in March and September are the two occasions each year when the day and the night are of equal duration. For measuring the length of a day, sunrise is the moment when the sun is half-above the horizon and sunset is the moment when the sun is half-under the horizon. Using this definition, the length of the day (and the night) is precisely 12 hours at an equinox. In the northern hemisphere, the March equinox is known as the vernal (spring) equinox and the September equinox is the autumnal (autumn) equinox. In the southern hemisphere, these names may be transposed. The northern vernal equinox typically falls on either 20 or March 21 and the autumnal equinox on 22 or September 23—the dates vary because the tropical year is not a whole number of days. Because the Earth's orbit is elliptical, the dates on which the equinoxes fall do not divide the year into equal halves. Egg balancing mythA common old wives' tale regarding the vernal equinox is that this is the one day of the year that eggs can be balanced on their end. While this myth is untrue (eggs can be balanced on any date with enough patience) and unsound (would it be different in the southern hemisphere? why not only the instant of vernal equinox? why not autumnal equinox?) it is often perpetuated in the news. Also by the same name:
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