NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars: Jupiter above the Moon
From: Frank Reed CT
Date: 2006 Jul 7, 16:53 -0500
From: Frank Reed CT
Date: 2006 Jul 7, 16:53 -0500
"How did you calculate and apply the flattening of the sun?" You get the refraction for the altitude of the Sun's center and then the refraction for that altitude plus the semi-diameter. The difference tells you how much the Sun's semi-diameter will be shortened in the vertical direction. Let's suppose it's 0.3'. Now if If the arc of the lunar distance was vertical --Moon directly above the Sun-- that's the correction. If th arc is 45 degrees away from vertical, the correction is half of this or 0.15'. In general, you multiply the vertical SD correction by the square of the cosine of the angle away from vertical. In practice, it is not even necessary to calculate that angle. You can estimate it when you take the sights to sufficient accuracy. Some 19th century tables included a simple look-up for this correction based on that estimated angle. Since the Sun and Moon have nearly the same apparent diameter, only one table is needed. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
