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Lewis and Clark lunars: more 1803 Almanac data
From: George Huxtable
Date: 2004 Apr 16, 17:33 +0100
From: George Huxtable
Date: 2004 Apr 16, 17:33 +0100
Has anyone else, I wonder, been struggling to resolve that doubtful lunar-distance observation made on the night of December 2-3, 1803, beside Bruce Stark, Mike Burkes, and me? So far, it seems clear that L&C must have made some big error(s), but we have not been able to establish what they are. Maybe they have misidentified some other star as Aldebaran. Rigel gives a much closer answer, but still not close enough. I have eliminated any of the four planets, which weren't near the right place at that time. The original message defining the problem was sent on 8 April, under the threadname "Lewis and Clark lunars: a request for help". It was followed up by some relevant information copied from the 1803 almanac in two mailings on 12 April. Now, with Bruce Stark's help, for which I'm grateful, I can add a bit more data from the 1803 almanac, giving Moon's semidiameter and Horizontal Parallax at some relevant times. Here is the 1803 Almanac data: Dec. 2nd. Midnight: SD 15' 38", HP 57' 21" Dec. 3d. Noon: SD 15' 31", HP 56' 55" Dec. 3d. Midnight: SD 15' 23", HP 56' 29" ======================================= If anyone else feels the need for further information from that almanac, I'm sure that Bruce and I, between us, can supply it. Below, copied once again below, is that star data and almanac data from around the time of that lunar distance observation, as previously posted on 8 April. Sorry all this necessary information been posted bit by bit. Yours, George. =========================================================== With the data from the 1803 almanac (copied again below), I forgot to include positions for Aldebaran and Regulus. These weren't taken from the 1803 almanac (I don't think star data was included in the almanac then) but were instead extrapolated backwards by 60 years, to the start of 1804, from an 1864 almanac that I have. They agree with predictions (with rates of change) extrapolated forward from 1765, from the first edition of Maskelyne's "British Mariner's Guide". Unlike the star positions in a modern almanac, which are provided at 3-day intervals to 0.1 arc-minutes, these are only mean positions of stars, allowing for precession and (where applicable) proper motion, but neglecting aberration and nutation. As a result, they are only good to the nearest 0.5 arc-minutes or so. Aldebaran. Right Ascension 66deg 10.3' or 4h 24m 41s; Declination N16deg 06.3' Regulus. Right Ascension 149deg 28.8' or 9h 57m 55s; Declination N12deg 55.2' Below, that earlier message is repeated. ========================= Relevant to those 1803 lunar distances by Lewis and Clark. I can quite some relevant extracts from the 1803 Nautical Almanac that I jotted down at my last library visit- Astronomical times and dates, of course, starting at noon each day, 12 hours after the start of the civil day with the same name and date. . All times Greenwich Apparent time. Sun RA Dec EOT (sub) 2 Dec noon 16h 30m 54.1s S21deg 53' 08" 10m 33.7s 3 Dec noon 16h 35m 13.9s S22deg 02' 07" 10m 10.5s Moon RA 2 Dec midnight 127deg 24' 20deg 05' 3 Dec noon 133deg 54' 17deg 50' 3 Dec midnight 140deg 08' 15deg 25' Lunar distances. Aldebaran West Regulus East Sun East 2 Dec midnight 58deg 00' 46" 22deg 19' 53" XV hrs 59deg 37' 27" 20deg 41' 16" XVIII hrs 61deg 13' 48" 19deg 03' 06" XXI hrs 62deg 49' 50" 17deg 25' 23" 120deg 36' 21" 3 Dec noon 64deg 25' 31" 15deg 48' 08" 119deg 06' 46" III hrs 66deg 00' 52" 117deg 37' 33" No doubt you're aware that EOT (Equation of Time) was then defined in the opposite way than we do it now. If there's anything else that anyone would find useful, I will note it down at my next visit. George. ================================================================ 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. ================================================================