NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
October Lunar
From: Jeremy C
Date: 2008 Oct 3, 08:42 -0700
From: Jeremy C
Date: 2008 Oct 3, 08:42 -0700
The sky cleared last night (October 2, 2008) for a bit, and a waxing crescent moon along with Venus appeared low in the Western sky just after sunset. It wasn�t an ideal situation for a lunar, but offered a chance to shoot one amidst the overcast days that have plagued me for the past week or so. Position is Lat 41deg 14.7�N , Long 075deg 53.0�W I checked the index error and found 0.9� on the arc and then proceeded to shoot 10 near-limb lunar distances. Without a horizon, I was stuck with calculating altitudes of both Venus and the Moon. Temperature is 50 degrees, but pressure is unrecorded. I have recently acquired Celestaire�s new version of the 7x35 scope, and it was my first time to use it on my sextant. (Thank you Ken for the opportunity to get one before I leave for sea next week). The extra magnification certainly helped in shooting the lunars, as was the steady shooting platform and low altitudes of both bodies. Admittedly, this was a poor time to shoot lunars. Both bodies were well below 10 degrees of altitude, and the observed lunar distances were just below 12 degrees, which does not usually help with accuracy, but I wanted to practice, so I proceeded. The observed Lunar Distances were as follows: LDs Time (UTC) 11deg 56.2 23h 13m 58s 11deg 56.8 23h 14m 50s 11deg 56.8 23h 15m 21s 11deg 57.1 23h 15m 48s 11deg 57.3 23h 16m 18s 11deg 57.1 23h 16m 52s 11deg 57.3 23h 17m 31s 11deg 57.6 23h 18m 00s 11deg 57.8 23h 18m 28s 11deg 57.8 23h 19m 00s Using Frank�s calculator for the reductions, I found an average error of 1.11� with the outside errors being 1.3� and 0.9�. Averaging the times and distances, I also got an error of 1.1�. Since all of the sights seem to have a good �grouping� ie accurate, the error in precision is the real question. Is it strange refraction due to low altitudes? Perhaps is an error in my sextant calibration, or perhaps just a personal observation error. I will have to shoot some more to see where the data point to. Jeremy --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---