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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robert H. van Gent
Date: 2023 Nov 29, 15:52 -0800
Repeating the same exercise with IMCCE's online ephemeris calculator ("Éphémérides de position")
https://ssp.imcce.fr/forms/eph
the aphelion distance is predicted as 35.1412239 au on 7 December 2023 at 18h 17.0m UTC.
Similarly, the greatest geocentric distance, 36.1140698 au, is computed to have occurred on 29 July 2023 at 14h 11.5m UTC.
Aldo Vitagliano's SOLEX software
http://www.solexorb.it/
predicts an aphelion distance of 35.140945 au on 7 December 2023 at 09h 36m 02s TT.
The greatest geocentric distance, 36.113802 au, is computed to have occurred on 29 July 2023 at 14h 11m 43s TT.
The lesson to be learned from these exercises is that the moment of the greatest geocentric distance can be predicted within a small fraction of a day while that of the greatest heliocentric distance can only be predicted to the nearest day or so. This is of course not surprizing, the Earth's orbit is much better known as that of Halley's Comet (which, when close to the Sun, is also perturbed by non-gravitational forces) and the Earth moves much faster in its orbit than Halley's Comet (on average) does.
rvg
