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Yesterday, October 29, a little before sunset here in Chicago, I did
some lunar distance sights using Alex E.'s SNO-T sextant by the lake
near Diversey Harbor. First I did a series of index correction sights
off the Moon. Carefully aligning the Moon images pole-to-pole, my
observations were (on arc, off arc):
33.1, 31.7
32.9, 31.3
32.7, 31.4
32.8, 31.2
Subtracting and averaging, I settled on an index correction of -0.75
minutes of arc.

The Sun was peeking between buildings near the lakefront and rather low
in the sky, so I had time for only three lunar distance sights as
follows:
GMT        LD
22:21:00  89d 57.8'
22:24:05  89d 58.8'
22:26:26  89d 59.4'
The last one looked a little unusual through the sextant since the Sun
was half-eclipsed by one the apartment buildings. Air temperature was
50F, reported pressure was 29.90in. Hg. Averaging the three
observations and clearing the result, I find an error of about -0.1
minutes of arc. That is, the observation was short by a tenth of a
minute of arc.

Generally, I like this sextant a lot. It's the first chance I've had to
try out this design. The inverting telescope is a great help for lunars
since it has good magnification, but it certainly takes a little
getting used to. For anyone on the list who may be unfamiliar with the
SNO-T, it is derived from the German Freiberger with little
modification, if I understand correctly, and it was apparently the last
production model for the Soviet Navy. The only flaw I find in it so
far, which I think bothered Alex, too, is that the micrometer has a
significant amount of static friction. It has to be nudged a bit to get
it moving. As it happens, the way I shoot lunars (and recommend
shooting lunars), this is not a real problem.

-FER
www.historicalatlas.com/lunars


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