AuthorTom Gaertner - Board President  It’s officially spring here in the northern hemisphere-- by both meteorological and astronomical definitions. Meteorological spring is based upon annual temperature cycles. According to the meteorological definition, and our weather forecasters, seasons begin on the first day of the months that include the equinoxes and solstices. Thusly, spring runs from March 1 to May 31; summer is from June 1 to August 31; autumn runs from September 1 to November 30; and winter lasts from December 1 to February 28. Astronomers base season cycles upon the position of the earth in relation to the sun. Spring begins on the vernal equinox; summer begins on the summer solstice; fall (autumn) begins on the autumnal equinox; and winter begins on the winter solstice. The beginning of each season marks the end of the last. The astronomical arrival of spring is a consequence of the earth’s tilt on its axis as it orbits around the sun. Equinox, from the Latin aequus (equal) and nox (night), means the earth’s two hemispheres are receiving the sun’s rays equally. The beginning of Astronomical Spring or the Vernal Equinox marks the time when the sun passes directly above the equator. The sun rises exactly due east and sets exactly due west, with sunlight striking both hemispheres of the earth equally. Night and day are approximately equal in length. Because the timings of the equinoxes and solstices change slightly each year, the length of astronomical seasons within a year and between years also varies. We can also look at seasons from a phenological perspective. It would be premature to pack away your winter outerwear, return the snow shovels to the shed or plant a garden outdoors. But as you observe the movement of the sun across the sky each day you will note that it is shifting toward the north. Birds and butterflies begin their northward migration as a response to this change in daylight, following the path of the sun. The arrival of the male red winged blackbirds to stake out their breeding territories is a harbinger of spring. If you happen to walk your leashed dog in the Forest, you know spring is also the beginning of mud season. What other signs of spring do you notice around the equinox? Record what you see in the Forest on our iNaturalist project page! |
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