NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars
From: Frank Reed CT
Date: 2005 Dec 9, 02:24 EST
From: Frank Reed CT
Date: 2005 Dec 9, 02:24 EST
Bill you wrote: "If you are not presetting to the the approximate separation, getting an initial rough alignment can be difficult. For stars at sea, some texts recommend inverting the sextant and viewing the star directly while moving the reflected horizon (much easier to see) into approximate position. Then flip the sextant and go for final alignment." Which raises a question, why flip it for the final alignment? Partly it's just less awkward, but it also highlights those two different methods of swinging the arc. And: "An observation: Frank's site rounds observation (lunar) error in 0.1' increments. If I recall, Frank stated the error in longitude was simply the observation error times 30. Since the errors in longitude are not multiples of 30, I would guess they are calculated prior to rounding the observation error. In which case, if you want to be really anal, divide the longitude error to get the actual observation error before rounding. For example, one of my observations showed -0.2' observation error and -5.0' longitude error. -5.0/30 = -1.67, better than the -0.2 would indicate. One -0.1 observation error showed a -4.4' longitude error. -4.4/30 = -0.147', so not as good as -0.1' would indicate." But remember, the clearing calculation can be no more accurate than the altitude corrections. The refraction is no more accurate than the nearest tenth of a minute of arc, so that's all there is in there. Dividing the longitude error by 30 may "look" more accurate, but those extra digits are just junk data. I think I should probably drop this "cheap" longitude error correction completely. And: " I warmed up the car while doing the observations, then brushed the snow off and scraped the ice from the windows before I went out to stock up on food and beer before the temperature became sub 0 on both the F and C scales." Hah. Myself, I'm hoping for a "forty below" this winter so that I can be the only guy in the room who knows that it's the same temperature on both scales. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars