NavList:
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Re: Fix by Occultations
From: Brad Morris
Date: 2009 Feb 7, 15:56 -0800
From: Brad Morris
Date: 2009 Feb 7, 15:56 -0800
Hi George You can find the low precision values of the Ecliptic Latitude and Longitude of the Moon in the Astronomical Almanac. The published values are to two decimal places of degrees. If you go to http://asa.usno.navy.mil/SecD/LunarPoly.html you will find the co-efficients to the Lunar Polynomials. When you use them, you will derive the high precision RA, declination and HP. The results can be converted (as you point out) to Ecliptic Latitude and Longitude. One issue I found, however, is that I had to add 180 degrees the ATAN function provided to obtain correlation. That is, the equation reads Ecliptic Long = 180 + atan(((sin(RA)cos(ObliquityEcliptic) + tan(dec)sin(ObliquityEcliptic))/cos(RA)) EXAMPLE 7June09 Polynomial Coefficients RA 245.4302085 13.3954668 0.0795003 -0.0392653 -0.0030594 0.0007151 Dec -25.6866823 -1.3663138 0.6207190 0.0099947 -0.0035461 -0.0000342 HP 0.91121504 -0.00532634 0.00057368 0.00001426 0.00000293 YIELDS (at midnight, we can easily shift the time) RA 245.4302085 Dec -25.6866823 HP 0.91121504 CONVERTING TO ECLIPTIC LAT LONG Elip Lat -4.110005927 Elip Long 247.9338333 The Astronomical Almanac 2009 publishes the 0h TT data as RA 16h 21m 43.25s Dec -25d 41m 12.1s HP 54m 40.37s Ecliptic Lat -4.11 Ecliptic Long 247.93 It seems to be worth while to go through the polynomial expansion, particularly if we intend to include the Limb Effects (mountains) like Frank suggests. Best Regards Brad --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---