A new week, another astronomical featured sight. This week, the topic is not so much something that one can see in the sky, but something that one will notice in the sky in the form of shortening days: the first day of fall. For anyone not keeping track, fall arrives this Friday, September 23, specifically at 5:05am. So, with the seasonal change, why do we have seasons at all?
Answer: it all has to do with the Earth’s 23 degree tilt. If the Earth were spinning on its axis with no tilt at all, everyone would be treated to days of identical length every day of the year, with latitudes nearer the equator having longer days than those nearer the poles. However, with the tilt, the angle of the Earth relative to the Sun changes as or planet moves about its orbit.
On the Autumnal Equinox, the Sun will rise/set exactly due East/West. The Sun will climb about 50 degrees high and the day and the night will be exactly 12 hours long (Equinox means ‘equal night’). After the equinox, the Sun will never leave the Southern celestial hemisphere until the next Vernal (spring) Equinox.
After the Autumnal Equinox, the shortening of the days will continue until the Sun finally reaches its most Southerly rise/set on the Winter Solstice, the shortest day of the year., which is around December 20. On this day, the Sun will rise/set low in the Southeast, get only about 25 degrees high (at Cleveland’s latitude) at local noon (at about 12:30 thanks to a return to Standard Time). The final result: a day that is only 9 hours long.
From that point on, the Sun will only get stronger, once again having an Equinox, the Vernal, around the 20th of March before culminating in its most Northerly rise of the year, the Summer Solstice, around June 20, at which point the Sun will peak at a height of about 72 degrees (Cleveland, again) at local noon (about 1:30pm). Result of the high-flying Sun, a 15+ hour long day.
So there it is, the mechanics of why we have the seasons.
For more info:
Video explaining seasons
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