Happy 1-AU Day!

Hey, everyone! Monday’s an exciting day for us fans of orbital geometry (and who isn’t, am I right?). It’s 1-AU day!

What?

Let’s see if I can do this in 100 words: GO!

Earth’s orbit isn’t a perfect circle. It’s a slightly elongated ellipse. The farthest point from the sun (aphelion) is in July; the nearest (perihelion) in January. As it moves between those, there are two points where Earth is exactly 92.96 million miles away. That’s the exact average distance from the sun; 1 astronomical unit (AU). From Monday through the summer, and clear out until October’s 1-AU day the distance from Earth to the sun will be farther than the distance from the earth to the sun.

img_3666

Phew. I did it! High five!

Happy 1-AU Day, everyone, have a great weekend, and clear skies!

Correction: I originally wrote 1-AU day was April 1. It was pointed out by my friend Marc, an actual astronomer, not a guy like me, that I had the wrong day: “the JPL Solar System ephemeris (which is as accurate as it gets in this world) has the Earth-Sun distance at 0.99999999989877 AU at 2017-Apr-03 16:39:33 UTC (to within one second — one second later and one second sooner the distance being further from 1 AU that the value at 19:39:33). BTW, (1.0-0.99999999989877) AU is 15 meters.

“This is unsatisfying, so I took the 3600 values (spaced at 1-second intervals) around it and fit a fifth-order spline to it and interpolated to the time corresponding to 1.0 AU. Turns out that’s 2017-Apr-03 16:39:33.031 UTC, the 1-millisecond precision corresponding to a distance error of about 7 cm.”

So, I’ve corrected the post so that it’s correct for tomorrow, April 3.

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