I enjoy amateur astronomical calculations. I calculate earth true anomaly and noticed a bug in my software just as earth passing through j2000 point and instead of going to 0 degrees it subtracting from 360.

But I checked wolfram alpha and with in a few days went from like 359 degrees now reports 179 degrees. If J2000 was 358 degrees or so, it should be very close to that or 0 degrees approx today, January 3, 2019?

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    $\begingroup$ Would Astronomy be a better home for this question? $\endgroup$
    – Qmechanic
    Jan 3, 2019 at 10:06
  • $\begingroup$ I'm not sure, it's really a question of precise mathematical notation for elliptical orbit. $\endgroup$ Jan 3, 2019 at 10:11
  • $\begingroup$ It probably may be a good or better place, they probably use it to determine exact position of stars for viewing. $\endgroup$ Jan 3, 2019 at 10:16
  • $\begingroup$ I dont know how to easily move question? $\endgroup$ Jan 3, 2019 at 10:16
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    $\begingroup$ Do you mean that PlanetData["Earth", "TrueAnomaly"] is calculating the wrong angle? Then this question should be raised on mathematica.stackexchange.com/questions $\endgroup$ Jan 3, 2019 at 13:14

1 Answer 1


I've found an almanac for earth perhelion up to 2100. 2019 perhelion occurred at roughly 5:00 January 3,2019. Thus the angle now of true anomaly is some extent past 0 degrees. And wolfram alpha is wrong by negative 180 degrees. By Wikipedia and other standard definitions of mean anomaly which have persisted sense Kepler's time.

While there does appear to be some deviation among sources, I find some in different time zone, on apparently from ny times reporting it occurred at a little after midnight January 3, 2019 which seems to correspond with a 5 am GMT time.


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