The winter solstice is upon us: Wednesday, December 21, will be the shortest day of 2016 for anyone living north of the equator (and Tuesday night will be the longest night of the year). If pagan rituals are your thing, this is no doubt a big moment for you. If not, the official first day of winter is neat for other reasons.
Below is a short scientific guide to the solstice and the longest night of the year (though not, as we’ll see, the longest night in Earth’s history — that happened back in 1912).
1) Why do we have a winter solstice, anyway?
Most people know this one. Earth orbits around the sun on a tilted axis (likely because our planet collided with some other massive object billions of years ago, back when it was still being formed).
So between September and March, Earth’s Northern Hemisphere gets…
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