Happy day the Sun has crosses the Celestial Equator into the Northern Celestial Hemisphere or, in layman's terms, happy first day of spring. Okay, now that everyone knows that spring is here, why do we have seasons at all?
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 Vernal 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 Northern Celestial Hemisphere until the next equinox, the Autumnal (fall) Equinox.
After the Vernal Equinox, the lengthening of the days will continue until the Sun finally reaches its most Northerly rise/set on the Summer Solstice, the longest day of the year., which is around June 20. On this day, the Sun will rise/set high in the Northeast, get only about 72 degrees high (at Cleveland's 41 degree North latitude) at local noon (at about 1:30pm thanks to Daylight Savings Time). The final result: a day that is over 15 hours long.
From that point on, the Sun will only get weaker, once again having an Equinox, the Autumnal, around the 20th of September before culminating in its most Southerly rise of the year, the Winter Solstice, around December 20, at which point the Sun will peak at a height of about 25 degrees (Cleveland, again) at local noon (about 12:30pm thanks to a return to Standard Time). Result of the low-flying Sun, a day a mere 9 hours long.
So there it is, the mechanics of why we have the seasons.
Note: depending on where you live, your days/nights may be of different lengths and the Sun's meridian transit will be lower/higher, with more Northerly latitudes having more extreme swings in apparent solar motion.
Want to have a little fun with your camera? Why not try a year long sunrise photo shoot?
Oh, yes, for people who think that the equinox doesn't matter now that we are in a highly technological world, consider this: Easter is going to be a very early one this year. Why? Simple, Easter Sunday is the first day after the first Full Moon after the Vernal Equinox. So, since this month's Full Moon falls on March 27, Easter will be the following Sunday.
Looking to do some sky watching in the Cleveland area? As the last part of the puzzle, be sure to keep an eye on the Cleveland weather forecast and, for hour-by-hour cloud predictions, the Cleveland Clear Sky Clock if you plan to head out and look at the stars this coming week. Live somewhere else? Find a clock and see if it will be clear near you.
For more info:
Video explaining seasons
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