It’s felt like it for weeks, but summer be­gins to­mor­row

Walker County Messenger - - Sports -

You may have no­ticed that me­te­o­rol­o­gists and cli­ma­tol­o­gists de­fine sea­sons dif­fer­ently from “reg­u­lar” or as­tro­nom­i­cal spring, summer, fall, and win­ter. So, why do me­te­o­ro­log­i­cal and as­tro­nom­i­cal sea­sons be­gin and end at dif­fer­ent times? In short, it’s be­cause the as­tro­nom­i­cal sea­sons are based on the po­si­tion of Earth in re­la­tion to the sun, whereas the me­te­o­ro­log­i­cal sea­sons are based on the an­nual tem­per­a­ture cy­cle. The As­tro­nom­i­cal Sea­sons The nat­u­ral ro­ta­tion of Earth around the sun forms the ba­sis for the as­tro­nom­i­cal cal­en­dar, in which we de­fine sea­sons with two sol­stices and two equinox­esPeo­ple have used ob­serv­able pe­ri­odic nat­u­ral phe­nom­ena to mark time for thou­sands of years. The nat­u­ral ro­ta­tion of Earth around the sun forms the ba­sis for the as­tro­nom­i­cal cal­en­dar, in which we de­fine sea­sons with two sol­stices and two equinoxes. Earth’s tilt and the sun’s align­ment over the equa­tor de­ter­mine both the sol­stices and equinoxes.

The equinoxes mark the times when the sun passes di­rectly above the equa­tor. In the North­ern Hemi­sphere, the summer sol­stice falls on or around June 21, the win­ter sol­stice on or around De­cem­ber 22, the ver­nal or spring equinox on or around March 21, and the au­tum­nal equinox on or around Septem­ber 22. These sea­sons are re­versed but be­gin on the same dates in the South­ern Hemi­sphere.

Be­cause Earth ac­tu­ally trav­els around the sun in 365.24 days, an ex­tra day is needed ev­ery fourth year, cre­at­ing what we know as Leap Year. This also causes the ex­act date of the sol­stices and equinoxes to vary. Ad­di­tion­ally, the el­lip­ti­cal shape of Earth’s or­bit around the sun causes the lengths of the as­tro­nom­i­cal sea­sons to vary be­tween 89 and 93 days. These vari­a­tions in season length and season start would make it very dif­fi­cult to con­sis­tently com­pare cli­ma­to­log­i­cal sta­tis­tics for a par­tic­u­lar season from one year to the next. Thus, the me­te­o­ro­log­i­cal sea­sons were born. The Me­te­o­ro­log­i­cal Sea­sons Me­te­o­rol­o­gists and cli­ma­tol­o­gists break the sea­sons down into group­ings of three months based on the an­nual tem­per­a­ture cy­cle as well as our cal­en­darMe­te­o­rol­o­gists and cli­ma­tol­o­gists break the sea­sons down into group­ings of three months based on the an­nual tem­per­a­ture cy­cle as well as our cal­en­dar. We gen­er­ally think of win­ter as the cold­est time of the year and summer as the warm­est time of the year, with spring and fall be­ing the tran­si­tion sea­sons, and that is what the me­te­o­ro­log­i­cal sea­sons are based on. Me­te­o­ro­log­i­cal spring in­cludes March, April, and May; me­te­o­ro­log­i­cal summer in­cludes June, July, and Au­gust; me­te­o­ro­log­i­cal fall in­cludes Septem­ber, Oc­to­ber, and Novem­ber; and me­te­o­ro­log­i­cal win­ter in­cludes De­cem­ber, Jan­uary, and Fe­bru­ary.

Me­te­o­ro­log­i­cal ob­serv­ing and fore­cast­ing led to the cre­ation of these sea­sons, and they are more closely tied to our monthly civil cal­en­dar than the as­tro­nom­i­cal sea­sons are. The length of the me­te­o­ro­log­i­cal sea­sons is also more con­sis­tent, rang­ing from 90 days for win­ter of a non-leap year to 92 days for spring and summer. By fol­low­ing the civil cal­en­dar and hav­ing less vari­a­tion in season length and season start, it be­comes much eas­ier to cal­cu­late sea­sonal sta­tis­tics from the monthly sta­tis­tics, both of which are very use­ful for agri­cul­ture, com­merce, and a va­ri­ety of other pur­poses.

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