A 1-AU Day Correction

Hi, everyone. Yesterday I wrote that it was 1-AU day (the day when the earth is exactly the average distance from the sun). Thanks for reading. Later in the day, my friend Marc, an actual astronomer, not a guy like me, pointed out 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.”

Much of this is beyond my math reach. Rather than be a peddler of fake news, I’ve corrected the post so that it’s correct for tomorrow, April 3. Sorry about that. I hope I didn’t ruin too many conversations.


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