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The pool have closed and crisp temperatures and crunchy farewell are on their style . Today ( Sept. 22 ) mark the death of summer and the get-go of fall , also called the autumn equinoctial point , in the Northern Hemisphere .
Theautumn equinoxoccurs today at 4:44 p.m. EDT ( 20:44 UTC ) when the sun is directly in cable with Earth ’s celestial equator , or the equator projected onto the sky . daytime and night last about evenly long on Sunday , with about 12 hours of luminosity and 12 hour of darkness . This same phenomenon occurs on thespring equinoctial point , which will next pass off on March 20 .
A carpet of fallen leave beneath nearly bare trees, with green grass in the background serving as a memory ofsummer gone by.
The day of the month of the gloam equinoctial point ( and its springiness twin ) varies somewhat each year , sometimes fall on the 23rd or 24th calculate on the quirks of the calendar , along with Earth ’s slimly irregular orbit . Here are five surprising facts about surrender and the fall equinox .
1 . Amazing light shows
In addition to the bright colouration of fall leaves , the autumn equinox signals another colorful spectacle — the aurora borealis , also called theNorthern Lights . Besides the lengthening of nights and cool evening weather , which are bully for stargazers , autumn really is " cockcrow season , " according toNASA . That ’s because geomagnetic storm are about twice as frequent as the one-year norm during the fall . [ Aurora Photos : Northern Lights Dazzle in Night - Sky Images ]
particle that get discharged from the sunlight during such geomagnetic storm aught toward Earth at breakneck speed . As the particles slam into Earth ’s magnetic field , they bump into corpuscle and molecules of O , atomic number 7 and other elements . The result ? dazzle light show , with hue most ordinarily of pink , green , yellow , blue , reddish blue and occasionally orangish and clean — depend on what ingredient the particles collide with .
2 . brute answer , testes swell
hold out things respond to the light-colored changes that get with gloaming , with tree shedding their farewell and animals preparing for hibernation . Fall can bring an specially noticeable modification to the high - attitude - livingmale Siberian hamster . That ’s because the gnawer ’s testes swell up 17 times their sizing from unforesightful days to long ; the swelling allows , in part , the fauna to time replication by rights .
Hamsters are n’t the only creatures to herald in fall in strange way . When autumn hits , the black - crest chickadee snuff it gangbusters gather cum and blot out them in one C of different spot in Sir Herbert Beerbohm Tree and on the ground . At the same time , the diminutive bird ’s hippocampus balloons by 30 percentage as Modern spunk cells pop up in this part of the brain , which is creditworthy for spatial organisation and memory .
3 . Full moon named for autumn
Autumn get its own full moon , theHarvest Moon . From Wolf and Sturgeon to Hunter and Harvest , full moons are named for the month or season in which they uprise . The Harvest Moon is the full moon close to the fall equinox , which occurred on the night of Sept. 18 - 19 this twelvemonth .
Before hokey lighting , farmers take reward of the full Sun Myung Moon ’s light to glean their crops . In belated summer and other autumn , many crops mature all at once , making peck of employment for Farmer who had to stay in the fields after sundown to harvest all the goods . Such moonlight became essential to their crop , and the Harvest Moon emerge , according to NASA .
4 . Why fall leaves may fade
mood alteration may tone down the picture most synonymous with autumn — fall foliage . Leaves change their closet in response to parky temperatures and less light ( as day begin to shorten ) ; they stop bring on chlorophyl , the greenish pigment that helps folio appropriate sunlight to power photosynthesis . As dark-green fade , the leave ’s other pigments , such as the orange and lily-livered of carotenoids shine through . Vibrant blood-red hues are the event of anthocyanins , pigments that are produced in the crepuscle . [ Photos of Turning Leaves : The Rich Colors of Fall Foliage ]
These autumn colors could be some of thecasualties of global thawing , say scientist . Research has shown as the reality warm up , fall - tinge leave-taking are delayed since their pool cue to alter colour come partly from cooling temperature .
Fall ’s coolheaded night and sunny days also facilitate to trigger trees like the sugar maple to store their anthocyanins temporarily in their leaves , giving leafage peepers a show of red . But if global thawing leads to ardent night , paired with autumn ’s shortening sidereal day , trees may not practice their sugar to make red pigments , instead station that fuel to twigs or burning it off , according to Howie Neufeld , a plant physiologist at Appalachian State University in North Carolina .
mood change may also alter suitable habitat for trees like the sugar maple known to be swelled players in pin ’s vivacious colors .
5 . When is the equinoctial point ?
Theautumnal equinoctial point falls on dissimilar dateseach year , usually Sept. 22 , like this twelvemonth , or Sept. 23 ; but in 1931 , the equinox happen on Sept. 24 . The reason : The Gregorian calendar does n’t match up perfectly with the position of Earth in its orbit around the Sunday .
As Earth orbits the sun , it revolves around its bloc at a 23.5 - degree angle so that it is pointed directly toward the sun at the summertime solstice , directly forth from the Lord’s Day during the wintertime solstice , and at a correct slant with the sun on the equinoxes ; that right slant think the sun shines about adequate amounts of light across the Northern Hemisphere on the equinoxes . If this trek around the sun take exactly 365 solar day , Earth would be in its autumn equinoctial point locating on the same twenty-four hours each year . Since Earth takes 365.25 days to make a arrant journey around the sunshine , the date is slightly different each year . The fall equinox wo n’t happen again on Sept. 24 until 2303 .
