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    Moon, Saturn, and stars last night
    From: Frank Reed
    Date: 2013 Jun 21, 11:37 -0700

    Here's a batch of observations from last evening taken at Stonington Point in Connecticut beginning about 15 minutes after the end of nautical twilight. Times are UTC. Height of eye was about 12 feet, maybe 9 feet relative to wave tops at the horizon. I was using my Tamay-alike sextant with a 7x scope.

    01:56:20 Moon UL 29°24.5'
    02:00:-- Moon dia. 33.2' IC=-0.2
    02:03:45 Moon UL 29°33.2'
    02:08:05 Saturn 35°57'
    02:11:10 Moon UL 29°39.8'
    02:14:03 Moon UL 29°40.6'
    02:17:13 Antares 20°43'
    02:20:30 Moon UL 29°42.6'
    02:23:00 Saturn 34°42'
    02:26:03 Moon UL 29°42.9'
    02:28:36 Arcturus 61°41'
    02:31:07 Moon UL 29°42.6'
    02:36:16 Moon UL 29°39.7'
    02:39:33 Arcturus 60°13'
    02:42:23 Moon UL 29°35.0'
    02:46:00 Moon UL 29°31.5'

    With the Moon UL observations, you can make a nice meridian curve. The latitude that results is reliable (within instrumental/observational error), but if you attempt to determine a longitude from the curve, you'll need to remember that that the Moon is heading South during these observations which would be just the same thing as the observing location moving northbound at some speed. If you correct for that, the adjusted center shows the GMT when the Moon was due South. At that instant, the Moon's GHA would be equal to my longitude.

    From a preliminary analysis, I find that the intercepts are mostly in the range from 0 to 2 nautical miles, though the Saturn observations are worse.

    The horizon under the Moon was fairly clear but it was noticeably brighter towards the right of the spot directly under the Moon. I couldn't see the horizon at all unless the Moon was heavily shaded. The horizons for the star sights were less distinct, but still clear. For the Saturn and Arcturus sights, I was using the faintly visible dividing line between very dark and black as pitch --the water and Fishers Island beyond. This should have been close to a real horizon, not a dip short.

    By the way, in the analysis of the Moon's diameter yesterday, I left out 0.1' of refractional flattening. The true vertical diameter yesterday should have been 32.7. Observations were 32.8 and 32.7 so still correct within a tenth. Last night's obs'd diameter was 33.2' and including augmentation and refractional flattening, I find that that's correct within a tenth also.


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