NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Historical Lunars : take in account 'delta-T' or ignore it ?
From: Marcel Tschudin
Date: 2009 Dec 14, 19:32 +0200
From: Marcel Tschudin
Date: 2009 Dec 14, 19:32 +0200
Antoine, > A possible explanation for the "discrepancy" you mentioned between the NAL > and AAL refraction values might come from the fact that AAL values are given > for a single given CONSTANT wavelenght, while NAL gives values for the > observed average wavelenghts - i.e. INCREASING WAVELENGHTS when heights > decrease - since all bodies apparent colors start moving towards "red" when > height decrease. This MIGHT be a resonable explanation. Any other > explanations from NavList Members ? The amount of reddening may however vary considerably. It likely is much stronger after the eruption of a volcano. It depends on the aerosol content in the air (Angstr�m exponent), a property which is since some time carefully observed world-wide: http://en.wikipedia.org/wiki/Angstrom_exponent or http://aeronet.gsfc.nasa.gov/index.html > Also, I find the following Center to Center separation velocities : > > GEOCENTRIC : .007664 d/minute (you specified .00767) and > > TOPOCENTRIC : .007767 d/min (you specified .00492). Something is unclear to > me here because apart from this specific topocentric result, all our other > values match quite closely. May be one result for a spherical earth and the other for an ellipsoidal one? Salutations Marcel -- NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com
