NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Interpolation to latitude
From: Joe Schultz
Date: 2009 Nov 9, 14:29 -0800
From: Joe Schultz
Date: 2009 Nov 9, 14:29 -0800
Hi Inuik, "Convert each LMT to GMT by adding... or subtracting .. the time equivalent of the expected DR longitude..." Mean time is directly correlated to longitude. In other words, the longitude correction is a direct calculation. I use a 4-2-1 memory aid: 4min time per degree longitude, 2min time per 30min longitude, 1min time per 15min longitude. For your exercise, I mentally calculate the longitude correction as: 50d15m - 45d longitude = 5d15m longitude = 4 five times plus 1 = 20 + 1 = 21m time. We are west of the zone meridian of 45d so we add the longitude correction to LMT to obtain the event zone time (ZT), then add another 3hr to obtain the event GMT. 3hr was another mental calculation: 15, 30, 45deg longitude = 1, 2, 3hr time. It's important to remember that latitude and longitude are not coordinate positions on the surface of the earth. They are angles, measured at the center of the earth. Distance on the earth's surface is correlated to latitude, and mean time is correlated to longitude. Interpolating for the latitude correction is a mathematical short-cut which isn't exactly correct, but is close enough for us in this type of exercise. Otherwise we'd spend all day just calculating the latitude correction. I do get the answers in your 10521 post. Hope this helps, Joe --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com -~----------~----~----~----~------~----~------~--~---