On Mon, 2021-04-26 at 13:05 -0700, Steve Allen via tz wrote:
On Mon 2021-04-26T12:42:19-0400 John Sauter via tz hath writ:
In looking at historical estimates of the rotation of the Earth based on astronomical observations of occulations and eclipses, I found that the values of UT1 are reliabe only since 1825. (Nevertheless, my table of proleptic leap seconds goes back to the year -2000.)
Morrison, L. V.; Stephenson, F. R.; Hohenkerk, C. Y.; Zawilski, M. DOI: 10.1098/rspa.2020.0776 Bibliographic Code: 2021RSPSA.47700776M Proceedings of the Royal Society A, Volume 477, Issue 2246, id.20200776 all tabulated at http://astro.ukho.gov.uk/nao/lvm/
That is the place to look, and it will continue to be so for the lifetime of the authors.
That is indeed the source that I used. The February 2021 update caused all of my projected leap seconds before 1825 to change, hence my caution about the reliability of astronomical observations before that date. I do not know personally the authors of that article, but based on their publishing history I will guess that the first two are of an advanced age. The February 2021 update was provided by C. Y. Hohenkerk, so perhaps the senior authors are passing the task on to the next generation. John Sauter (John_Sauter@systemeyescomputerstore.com) -- get my PGP public key with gpg --locate-external-keys John_Sauter@systemeyescomputerstore.com