I was reading through the Wiki pages on tests of relativity and I was curious about this section. Am I interpreting it correctly? Is there still about $1.21''/\text{ cy}$ of precession (Total Predicted: $575.31$ - Total Observed: $574.10$) that are not predicted by GR? The reference is from 1947. Does anyone have a more recent measurement and/or prediction?

Edit: My apologies. I transcribed the difference between the observed and predicted incorrectly. I've updated the question with the right values. Sorry for the inconvenience.

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    $\begingroup$ Can you clarify where you're getting this number from? I don't see it appear in the link nor can I come up with any reasonable combinations of numbers therein which would lead to the number you've specified. $\endgroup$ Commented Feb 17, 2021 at 20:26
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    $\begingroup$ Physicists don’t get too worried about $2\sigma$ discrepancies. $\endgroup$
    – G. Smith
    Commented Feb 17, 2021 at 20:26
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    $\begingroup$ What they said. The difference in that table between the predicted value and the upper observed value is 0.56" per century. Also note that there are two citations attached to that table, one from 2017, and one from 1947, and it's not unusual for Wikipedia to have inconsistent data in the same article, although (admittedly) data in a single table is less likely to suffer from that problem. $\endgroup$
    – PM 2Ring
    Commented Feb 17, 2021 at 21:40
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    $\begingroup$ Please state the values and not only their difference. By the way, this paper addresses the issue: nature.com/articles/320039a0 $\endgroup$
    – my2cts
    Commented Feb 17, 2021 at 22:37
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    $\begingroup$ Actually in the table in your reference I see a difference nog 1.21"/cy. $\endgroup$
    – my2cts
    Commented Feb 17, 2021 at 22:47

1 Answer 1


The wikipedia section on the precession of Mercury's orbit is in serious need of an update. The presented observational data is centuries old. Its main reference is the Clemence paper from 1947. Since then the astronomical data have been updated to give a GRT prediction of 42.98"/cy. Clemence gives a slightly higher value. The other two relevant numbers are the Newton predictions on the precession without the GRT effect and the observed precession. The difference of these is the anomaly to be explained by e.g. GRT. The Clemence paper relies on Newtonian calculations from 1911 and observation data from 1863. A modern prediction of the total precession including the effect of GRT is given in this open access paper. The reported number (575.31"/cy) is also given in the wikipedia article (just added extra ref). I am still searching for modern observational data. The 43"/cy number is far too important to rely on very old observations. There must be more modern information. I hope the Bepi Colombo mission will also address this. I will update this answer when I find anything.

  • $\begingroup$ This seems like the type of thing that would be in one of Clifford Will's review papers. $\endgroup$ Commented Feb 18, 2021 at 22:16
  • $\begingroup$ @JerrySchirmer Do you have a reference? $\endgroup$
    – my2cts
    Commented Feb 18, 2021 at 22:22
  • $\begingroup$ hyperspace.uni-frankfurt.de/2014/06/12/… Amongst others. Will's done a lot of work on tracking GR experiments. $\endgroup$ Commented Feb 19, 2021 at 0:09

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