The summer solstice is upon us: Tuesday, June 20, will be the longest day of 2017 for anyone living north of the equator. If pagan rituals are your thing, this is probably a big moment for you. If not, the solstice is still pretty neat.
Below is a short scientific guide to the longest day of the year (though not, as we’ll see, the longest day in Earth’s history — that happened back in 1912).
1) Why do we have a summer solstice, anyway?
Okay, most people know this one. Earth orbits around the sun on a tilted axis (probably because our planet collided with some other massive object billions of years ago, back when it was still being formed).
So between March and September, Earth’s Northern Hemisphere gets more exposure to direct sunlight over the course of a day. The rest of the year, the Southern Hemisphere gets more. It’s the reason for the seasons:
In the Northern Hemisphere, “peak” sunlight usually occurs on June 20, 21, or 22 of any given year. That’s the summer solstice. By contrast, the Southern Hemisphere reaches peak sunlight on December 21, 22, or 23 and the north hits peak darkness — that’s our winter solstice.
Technically speaking, the summer solstice occurs when the sun is directly overhead the Tropic of Cancer, or 23.5° north latitude. Like so:
In 2017, this will occur at exactly 12:24 am (Eastern) on the 21st. (But we’ll celebrate on the 20th anyway.)
2) How many hours of sunlight will I get on Tuesday?
On the off chance you live near the Arctic Circle, the sun never really sets during…