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    Re: Lunars: 10/27/2013
    From: Frank Reed
    Date: 2013 Oct 28, 09:25 -0700

    For your sights, I find the following errors on each individually:

    The average error, which could reflect the actual IC for your instrument, is -0.5'. The standard deviation, such as it is for a small sample, is 0.3'. These are very good results for any sextant and excellent results for a Davis plastic sextant. If you want to think in terms of GMT and traditional lunar sights, just remember that each tenth of a minute of arc corresponds to about 12 seconds of GMT. So you be optimistic and say that your "lunar clock" is only off by 24 seconds (either of the first two), or you can use the average and say that you're off by 60 seconds. The first would imply an error of longitude of only 6' or 5 nautical miles in your latitude, the latter would imply an error of 15' of longitude or 12 nautical miles. In either case, certainly more than adequate for navigation by 18th or 19th century standards, and not too shabby even for 21st century navigation. Nice work! Next, before we lose the Moon for a week, if you can get up before sunrise, you should try some Moon-Jupiter lunars.

    By the way, while you were shooting lunars, I was talking about them. This past weekend was one of my "19th Century Methods" classes. We were actually doing local time "time sight" calculations primarily while you were shooting lunars, but with some lunars discussion thrown in for fun. About an hour later, we shot some Sun sights, and I did at least point out the Moon in the sky before it was obscured by a few pesky clouds in the west. :)


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