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    Re: Attempting to decipher a "time sight"
    From: Sean C
    Date: 2016 May 28, 06:54 -0700

    Doug,

    I, too, was recently trying to make sense of the time sights in the Morgan workbook. Just be glad you picked the example you did. I was also confused by the way the times were noted, but the sight I chose was early in the morning, Greenwich time. The navigator had noted it as '13"49"11', which led me to believe it was near 2 in the afternoon. It wasn't until later (after much confusion) that I remembered that the navigation day used to start at noon. Therefore, morning times in the workbook appear to be written as modern afternoon times on a 24 hour clock. So, in the example I chose, Greenwich time was actually 01:49:11 A.M.

    I think most of your analysis is correct. The 11' correction is close to the 12' "standard" correction for sun sights. Why the navigator chose to use 11' in some places and 12' in others is a mystery to me. Looking at images of the Charles W. Morgan, it seems unlikely that he would've used a dip correction of just 3'. As for the difference in declination, I have also found some deviation from expected values. Perhaps the navigator was using an independently published almanac, as others have discussed, which was itself in error and/or he didn't bother to interpolate? Or maybe it was just a mistake on the navigator's part. On page 9, he figures a difference of 10h47m50s is equal to a longitude of 151°57'. Unless I'm missing something, this should've been 161°57'...a full 10° off. So, it seems he wasn't immune to the occasional blunder.

    I also have no clue as to what entries "A" & "B" could be, or why he wrote "3:35 P.M." at the top of the page. Maybe this was the time when he sat down to work the calculations? Similar times appear sporadically on the next few pages and seem to have little relation to the calculations themselves.

    Cheers,

    Sean C.

       
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