NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Homemade octant
From: Frank Reed CT
Date: 2006 Mar 19, 21:30 EST
From: Frank Reed CT
Date: 2006 Mar 19, 21:30 EST
Greg, you wrote: "It seems to be +/- 1 minute of arc. I can't tell where the error comes from - but in the end it comes out within +/- 1 min of my MAC." That's excellent. Honestly though, even your M.A.C. may not be that accurate over its whole range. Have you tested your octant for large angles? Say, above 70 degrees? You asked: "but lets say on the avg, to the nearest min. My experiments with running the calculations, shows varying the Ho or Lat by 1min can move the AP about 4 miles. There are different combonations; Ho+ Lat=0, H0+ Lat+, Ho- Lat -, etc., etc. some give better results; but 4 miles is a safe number when speaking of errors. Was this as good as it got ( Talking in period c 1800 if using a octant or sextant with this resolution)? and didn't you need to resolve down to 10" or 20" to do lunars?" A mile or two accuracy in latitude was (and still is today) a reasonable expectation. Even a perfect sextant with perfect input data is still limited by the vagaries of terrestrial refraction which makes the horizon variable by about one minute of arc. Note that sextants were developed specifically to measure large angles and to measure them at an accuracy about ten times better than you can do with an octant. Octants were used for measuring altitudes. Sextants were used for measuring lunars (which are not affected by terrestrial refraction). After 1850 (-ish) sextants were used for more or less all observations. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars
