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Re: equinox
From: Dan Allen
Date: 2004 Mar 21, 12:30 -0800
From: Dan Allen
Date: 2004 Mar 21, 12:30 -0800
And my best implementation of Meeus has it at 20 Mar 2004 at 6:44:23 UTC, for both zero degrees of declination and zero hours of right ascension, but apparently this time is off by 4-5 minutes. The Astronomical Almanac should be more accurate than the Nautical Almanac, as the Nautical Almanac does adjust GHA somewhat as you note. Every year I am frustrated by the lack of agreement on when Spring starts. Dan -----Original Message----- From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Fred Hebard Sent: Sunday, March 21, 2004 12:21 PM To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM Subject: Re: equinox My calculation was based on the Nautical Almanac, which had a 0 degree declination for the Sun exactly at 6:48:00 UT. The Sun's GHA is adjusted by up to 1.5' to reduce the error arising from ignoring the v correction. The GHA of the Sun may be in error by up to 0.25'. MICA reports: Sun Apparent Topocentric Positions Local Zenith and True North Location: E 79?51'26", 0?00'00", 0m (Longitude referred to Greenwich meridian) Date Time Zenith Azimuth Distance (UT1) Distance (E of N) to Object h m s ? ' " ? ' " AU 2004 Mar 20 06:48:00.2 0 00 02.4 111 21 02.9 0.995960666 2004 Mar 20 06:48:00.3 0 00 01.1 141 03 00.3 0.995960666 2004 Mar 20 06:48:00.4 0 00 01.2 223 27 24.7 0.995960666 2004 Mar 20 06:48:00.5 0 00 02.5 249 45 07.1 0.995960667 The Naval Observatory reports 6:49 for the vernal equinox: 2004 2004 Perihelion Jan 4 18 Equinoxes Mar 20 06 49 Sept 22 16 30 Aphelion July 5 11 Solstices June 21 00 57 Dec 21 12 42 Perhaps one of the astronomically literate will explain the discrepancy. On Mar 21, 2004, at 2:01 PM, Gary Harkins wrote: > In a message dated 3/21/2004 1:23:55 PM Eastern Standard Time, > legras@MAD.SCIENTIST.COM writes: > spring equinox was on earth 20/03/2004 at 06:49 utc according to Jean > Meeus' sky calender 2004 > > On which planet does it occur at 6:48 ???? > > Using the Nautical Almanac and interpolating between .8' South at 0600 > utc and .2' North at 0700 utc the equinox calculates to occur at > exactly 0648 utc. Are you saying that Jean Meeus' sky calendar is > more accurate than the nautical almanac? Does he carry his > calculations out to more precision than .1' of declination? And who > cares anyway, it's cold as most winter days here regardless of what > the calendar says.