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Re: Tycho Brahe Mars oppositions
From: George Huxtable
Date: 2004 Dec 4, 00:00 +0000
From: George Huxtable
Date: 2004 Dec 4, 00:00 +0000
Michael Dorl wrote- >When George first showed us the Meeus numbers, he said "The times are in >TD...." What is meant by TD? I know about TDT, ET, UT, and the others >stuff in section B of the Astronomical Almanac but TD is not described >there. I guess the times I list above as TDT should really be called ET >since they are pre 1984. Response from George. Precise time has long been in the custody of the French, and I guess that TD is short for "Temps Dynamique" or Dynamic Time. It comes in two slightly-different flavours, TDT or Terrestrial Dynamic Time, and TDB or Barycentric Dynamic Time, depending on whether or not a tiny relativistic correction is accounted for. They are so similar that not even Meeus bothers to differentiate between them, using simply TD instead. There's no practical difference, from our point of view, between Ephemeris Time (ET), Atomic Time, and either version of Dynamic Time (TD). Meeus explains, at the start of Chapter 10. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================
