On the 22nd of this month, people living in the Northern Hemisphere will be treated to the longest night of the year courtesy of the Winter Solstice. So why does the day change length 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 Winter Solstice, the Sun will rise/set at its most Southerly point of the year. The Sun will climb about 25 degrees high (at Cleveland's 41 degrees North latitude) and the result will be a day only about 9 hours long. After thesolstice, the Sun will not move much in the next month or so (‘solstice’ comes from the Latin words meaning ‘Sun stands still’). Don’t expect any noticeable lengthening of the days until around the start of February.
However, from the point of the solstice on, the Sun will only get stronger (albeit too slowly for most) as it moves toward the Vernal Equinox around the 20th of March, at which point the Sun will climb about 48 degrees up (Cleveland latitude), rise/set exactly due East/West for a day/night exactly 12 hours long. From there, the Sun will enter the Northern hemisphere, culminating in its most Northerly rise of the year, the Summer Solstice, around June 20, at which point the Sun will take a high (72 degres up in Cleveland), long arc across the sky for a day about 15 hours long.
So there they are, the reasons we have seasons.
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