On Thu 2007-01-18T00:40:56 -0700, M. Warner Losh hath writ: > "Thus UT1 is not, strictly speaking, a form of solar time"
This was the point made by Aoki et al. in 1982 http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1982A%26A...105..359A when they replaced Newcomb's expressions (which had been based on observations of the sun) with a new interpretation of what Newcomb had actually done. Then in 2000 Capitaine et al. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...355..398C further removed the sun from the equation. Despite being so openly acknowledged in the literature this deviation from "solar" time eluded even Jean Meeus until around 2005; look for a pointed example in his next book on computational astronomy. The current expression for UT1 will do well enough for civil time until leap seconds would have to be happening every month. One might wonder whether, in the light of modern measurements, Newcomb would opine that his expression was supposed to be solar time. The slop of a full second in UTC made the original meaning of UT1 moot, and the geophysicists took the advantage. -- Steve Allen <[EMAIL PROTECTED]> WGS-84 (GPS) UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99858 University of California Voice: +1 831 459 3046 Lng -122.06014 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m