NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Oblateness correction
From: George Huxtable
Date: 2010 Nov 30, 20:36 -0000
From: George Huxtable
Date: 2010 Nov 30, 20:36 -0000
Lars wrote- From: "Lars Bergman"To: Sent: Tuesday, November 30, 2010 5:42 PM Subject: [NavList] Oblateness correction In the Sight Reduction Procedure chapter in the Nautical Almanac, the correction for the oblateness of the earth, to be added to the Moon's parallax in altitude, is given (in degrees) as OB = -0.0032 (sin Lat)^2 cos H + 0.0032 sin (2 Lat) cos Z sin H where H is apparent altitude, Z true azimuth in the range 0 ... 360 and Lat is latitude in the range -90 ... 90. Now, in the second term the sine of two times latitude gets different signs depending on hemisphere. Shall it be like this, or ...? Lars, 59N 18E ============= Lars is worried about apparent lack of symmetry of this correction, between Northern and Southern hemispheres. But if he takes two situations, in which the positions of the Moon and the observer have both been reflected about the equator, then the azimuth of the Moon, as seen by the observer, will be shifted into a different quadrant, reversing the sign of Cos Z, and thus undoing any asymmetry. Is that an answer? George. contact George Huxtable, at george{at}hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.