December Solstice 2019
On Saturday, December 21 at 11:19 p.m. EST (December 22 at 04:19 GMT), the Sun will reach the solstice — its southernmost declination for the year, resulting in the shortest day of the year for the Northern hemisphere, and the longest day of the year for the Southern hemisphere.
This solstice marks the start of winter in the Northern Hemisphere, and the start of summer in the Southern Hemisphere. At that precise moment, the north pole of Earth’s axis of rotation will be tilting directly away from the Sun. Every day at local noon the sun reaches its highest position (or culmination) in the sky for that day. But on the December Solstice, that position is the lowest for the entire year. The low culmination also means that the sun needs less time after sunrise to reach noon – so Northern Hemisphere dwellers receive the shortest duration of daylight and the longest nights for the year. The sunlight that northerners do get this at time of year is also weaker because it’s spread over a larger area.
Fewer hours and weaker sunlight result in less received solar energy (insolation) and therefore colder temperatures. It is not the case, as some people think, that the days are colder in winter because we are farther from the Sun (a position called aphelion). That event happens every year in early July. On the contrary – Earth’s minimum distance from the Sun (perihelion) occurs every January 4, or thereabouts.
After the December solstice, days will slowly start to grow longer again in the Northern Hemisphere. For the Southern Hemisphere, the sun will attain its highest noon-time height for the year on the December solstice, and kick off their summer season. Their winter will commence six months from now, at the June Solstice.
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Have a Happy Solstice and a Merry Perihelion!