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Re: nautical almanac first point of aries
From: Geoffrey Kolbe
Date: 2012 Mar 12, 21:26 +0000
From: Geoffrey Kolbe
Date: 2012 Mar 12, 21:26 +0000
In a sidereal reference frame, the earth rotates 15 degrees 2.5 minutes in one hour, not 15 degrees dead.... Just out of interest, my Long Term Almanac predicts a GHA angle of 80 degrees 46.9 minutes for 1800 hrs today. Not bad, considering I compiled it 13 years ago now. Geoffrey Kolbe At 18:17 12/03/2012, you wrote: >Greetings, > >I have been looking at the online nautical almanac at >http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.isa/pages?date=03/12/2012 > >and for today monday 12 mar 2012 the GHA angle for aries is 80 >deg 47.1 min at 18:00 h GMT > >I think I can convert the GHA for aries to time and that should be the >same as sidereal time at Greenwich. > >( (80./15) + (47.1/60)/15 ) = 5.38566... >taking the 5 out and mult the fractional part by 60 .3856666 * >60 = 23.1399... >and taking out the 23 and doing the same .13999 >* 60 = 8.3 > >I used this web site to get sidereal time at longitude 0 deg 0 min >http://tycho.usno.navy.mil/cgi-bin/sidereal-post.sh >and pressed compute at approx. 16:00:00 GMT > >05:23:45.4 > > >The seconds are not in close enough agreement which makes me think I am >missing something or have made an error in the computations?