Talk:Ephemeris time

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Should the correct title of this article be "Ephemeris time" or "Ephemeris Time"? The article is at the former title, but the text uses "Time". If someone knows, I can change or move it accordingly. -- Infrogmation 14:39, 24 August 2005 (UTC)

I believe it should be "Ephemeris time". There were articles under both names, and I merged them together here, so there may be a relic 'Time' left. Salsb 15:31, August 24, 2005 (UTC)

[edit] When adopted?

Using the information that ET and TAI were already 32.184 seconds divergent when TAI was adopted in 1958, and a rough guesstimate of average increasing divergence of 0.7 seconds per year, it looks as if the divergence between UT and ET was first recognized around 1912. Could we add information to this article about when ET was first adopted, and when its divergence from UT was first recognized? arkuat (talk) 15:32, 18 May 2008 (UTC)

WP:RD/Science gave me the hint that Simon Newcomb was probably involved. arkuat (talk) 02:59, 19 May 2008 (UTC)

Further info, copied from the Reference Desk:

Ephemeris Time (ET) was so named because it was the independent time scale used in government ephemerides from 1900 through 1983, in the American Ephemeris and Nautical Almanac, the British Nautical Almanac and Astronomical Ephemeris, the French Connaissance des Temps, the German Astronomisches Jahrbuch, and the Spanish almanac. ET was defined (but not named) by Simon Newcomb in 1895/98 as the weighted average of mean solar time referred to the Royal Observatory, Greenwich between 1750 and 1892. It was implemented at Greenwich mean noon on 31 December 1899 (0 January 1900), meaning that from that date on the stated positions of the planets in the ephemerides would be calculated in terms of ET, not in terms of Greenwich mean solar time (named UT in 1928) which had been used before 1900. ET differs from UT quadratically, not linearally, that is, the difference is generally a parabola. See ΔT. However, this divergence was not recognized in 1895, instead its implemention included a "great empirical term", a sinusoid with a period of 257 years. — Joe Kress (talk) 08:09, 19 May 2008 (UTC)