NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: George's test
From: Alexandre Eremenko
Date: 2004 Nov 13, 18:24 -0500
From: Alexandre Eremenko
Date: 2004 Nov 13, 18:24 -0500
Dear Fred, Thank you for examining my report. On Sat, 13 Nov 2004, Fred Hebard wrote: > > Sextant upright position: > > Up Low Sum IndEr > > > > 32.5 32.5 65 0.0 > > 32.5 32.4 64.9 -0.05 > > 32.4 32.4 64.8 0.0 > > > > Sextant upside down: > > Up Low Sum IndEr > > > > 32.4 32.4 64.8 0.0 > > 32.5 32.6 65.1 +0.05 > > 32.7 32.3 65 -0.2 > > > Alex, > I don't understand from where you are drawing > the conclusion that you > have a random human error of 0.3' for the sun. You understood it correctly: I was talking about the SPAN (range) of the results in a series of similar observations. For example, the first column of the upside down series has span of 0.3'. The second column has also span of 0.3'. I agree it was somewhat incorrect to call it "random error of 0.3". The random error of plus or minus .15 will give such results. > It would appear you are not very > good at operating the sextant upside down, > but quite proficient right > side up. That's plausible. Upside down position is somewhat less convenient: the screw is on top etc. > Measuring the sun's semidiameter with the sextant in various > orientations does seem to be good practice for taking lunars. Taking lunars themselves, as well as star-to-star distances whold be even better practice. My purpose here was to check the rigidity of my sextant. > How about sideways or > at a 45 degree angle? Also tried. Norie (1828) recommends horizontal sextant position when measuring the index error from the Sun when the Sun is low (because the vertical SD and the round shape of the low Sun may be seriously distorted by refraction). > By the way, I get numbers similar to your right > side up measurements on > dry land, With what sextant and scope? >but, thus far, they are much worse on the >water. Unfortunately, I have no possibility to go sailing, at least until next summer. I still have much less success with another exercise: to determine my arc correction from star-to-star distances. The results I obtain are inconsistent. I mean the "span" is too large. Alex.