NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: sight reduction calculator
From: George Huxtable
Date: 2008 Jun 21, 20:47 +0100
From: George Huxtable
Date: 2008 Jun 21, 20:47 +0100
Gary LaPook wrote- | I have no idea how it could take ten minues to calculate Hc and Zn on a | pocket digital calculator, I just did a sample test and it took me 58 | seconds. I use the standard formula for Hc rearranged to the form: | | Hc = arcsin (cos LHA x cos dec x cos lat + sin lat x sin dec) | | and Z = arcsin (sec Hc x sin LHA x cos dec) since implementing it this | way saves a few keystrokes. Well, using that formula for Z doesn't necessarily give Gary an unambiguous result, seeing that the sine of 80� is identical to the sine of 100� (for example). How would Gary distinguish between them, without some additional keystrokes? Observing the azimuth isn't easy if the altitude is high. He would be better off using a formula that gives Z from its cosine, (or better still, from its tan, in which case it isn't even necessary to precompute Hc). George. contact George Huxtable at george@huxtable.u-net.com or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
