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Measurement of the Earth's rotation from 720 BC to AD 2015
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source: http://astro.ukho.gov.uk/nao/lvm/

Her Majesty's Nautical Almanac Office

This resource provides the results of the modern (updated in 2020) analysis of eclipse and 
occultation timings from ancient Babylonian, China, and the Arab and European worlds 
through early telescope observations to modern observations in the following papers:

Measurement of the Earth's rotation: 720 BC to AD 2015, published in 2016 in the 
Royal Society's Proceedings A 472, and made freely available via Open Access, 
by Stephenson, F.R., Morrison, L.V. and Hohenkerk, C.Y..

and updated in

Addendum 2020 to `Measurement of the Earth's Rotation: 720 BC to AD 2015', 
published in 2021 February in the Royal Society's Proceedings A 478, 
by Morrison, L. V., Stephenson, F.R., Hohenkerk, C.Y. and M. Zawilski, M..

Download the file of FAQs to get some general information about the paper.

The analysis provides measurement of the rotation of the Earth and allows formation of the 
change in the length of day (lod), relative to the standard day of 86400 SI seconds, 
and DT(t), the difference (using current terminology) between TT and UT1, 
via a spline fit using a weighted least-squares analysis of the data.

For comparison with EOP series, we make them consistent with UT1 - TAI determined after 1958, 
adding to UT1 - TT the offset TT - TAI = 32.184s at the date 1958 January 1. 
So IERS EOP-PC provides DT'(t) = -DT(t) + 32.184 s.    
 
The values of DT in the tables listed in the various sections should be used in conjunction 
with lunar ephemeris designated JPL DE430/LE430 in which the tidal acceleration of the Moon is
-25.85"/cy2.

The menus below allows users to access all the data used in this Addendum 2020, which consists 
of both new and updated data as well the data from the original 2016 Royal Society paper.