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Re: Lunars with Young's formula: always off by several minutes
From: Paul Hirose
Date: 2018 Nov 4, 21:12 -0800

On 2018-11-02 16:15, William Porter wrote: > > *Moon-Aries 19Oct18 18:46:47U Obs distance (near): 41deg 16.8’* > Lat: 51.432 deg Long -0.219 deg > *Ephemera:* > Moon (from USNO polynomials) > RA: 332.155 deg Dec: -13.891 deg HP:3274” AD:1784” I don't agree. First, the time. I assume "19Oct18 18:46:47U" is UTC. Currently UTC is 37 seconds behind TAI, and TAI is a fixed 32.184 s behind Terrestrial Time. Therefore, TT at observation time = 18:46:47 + 37 s + 32.184 s = 18:47:56.2 = .783289 day. The applicable polynomial coefficients are: R.A. 322.7938744 12.0578390 -0.1199279 0.0092096 0.0018500 -0.0000684 Dec. -16.3099733 2.8134374 0.3553752 -0.0179380 -0.0005172 -0.0000195 H.P. 0.9060852 0.0032932 0.0013016 -0.0000520 -0.0000059 (http://asa.usno.navy.mil/static/files/2018/lunarpoly_2018.txt) With a calculator and the polynomials I get geocentric apparent coords: 332.1701° -13.8970° RA, dec (true equator and equinox of date) .9094° (3274″) HP An independent computation with my astronomical software confirms those values. The position is .95′ different from what William got. I do agree with his parallax. Don't know what his AD:1784” means. > Aries > RA J2000: 19:50:47=297.696deg > *PLUS TO A FIRST ORDER APPROX, 18.8years’ precession at 360/25771 deg year=0.263deg=297.959deg* > *Thank you Navlist for helping me find this error* > Dec, ignoring precession for now: 8.868 deg > GST-UT: 1:52:47 (from astropixels.com) The Aries computation I will skip since I don't know what's going on. > 1) Preparation > GST (GHA Aries) = 20:39:34 = 309.890 deg > GHA moon = 337.735 deg > GHA Altair = 12.194 deg > “d”, observed distance = 41.528 deg after adding semi-diameter My geocentric values: 309.8858° Greenwich apparent sidereal time 337.7156° GHA Moon 11.9647° GHA Altair (UT1-UTC is negligible since it's only 32 milliseconds.)

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