Happy Perihelion!

5… 4… 3… 2… 1… Happy Perihelion! Hey, Perihelion is important. It certainly makes a lot more sense than that thing you did three days ago which was, what, a week after that winter solstice celebration that’s not even on the solstice anymore but that’s OK because nobody remembers it’s a solstice holiday anyway? Yeah, like that‘ll ever catch on. At least Perihelion means something.

Perihelion is the point at which an orbiting body (in this case, Earth) is closest to the Sun. See, the orbit of Earth (and pretty much everything else) is not perfectly circular.

Sometime in July, Earth reached the top of its orbit (about 152 million km), arced over gracefully and started falling back down toward the Sun. Now, about 6 months later, Earth is whipping around the Sun at top speed, sling-shotting back to that peak point next July. Right now, we’re 5 million kilometers closer to the Sun than we were 6 months ago. Which sounds much more impressive than “3% closer”.

This year, Perihelion is at 8pm (EST) on January 4th. It wobbles around a bit on the calendar and even drifts a bit relative to the winter solstice. There are all sorts of reasons for this, involving apsidal precession and ratios of revolutions to orbits. But what it really comes down to is this: Orbital mechanics doesn’t give a crap about calendars.

But today, right now, the Earth is at the lowest point of its orbit. So, to all the science geeks out there, Happy Perihelion! Or, as the rest of the world calls it, Wednesday.