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    Re: Perpendicularity check
    From: Frank Reed CT
    Date: 2004 Sep 24, 21:35 EDT
    Fred H wrote:
    "I also checked
    the sextant with some careful altitude shots and was out by less than
    0.05+/-0.23' & 0.14+/-0.30' of arc (mean and std deviation of three
    reps each) at sextant angles of 38 and 100 degrees, respectively.  I
    don't think it's the sextant; it's given pretty accurate altitude shots
    with one telescope that is properly aligned.  Operator error of some
    sort, unless it's the shades."

    It might be the shades. Try doing an index correction with the Moon (best when it's full, but probably do-able with our present gibbous moon). First try it with no shades. Then use each shade in turn and see if you get a significantly different I.C. Shade error adds linearly so if you find errors of +1, +1, and -0.5' on the upper shades individually, then when you use them all on a Sun sight, the correction woud be +1.5'.

    You also wrote:
    "In observation #37, I reset the index arm between the second and third
    shots and the fourth and fifth."

    How do you mean? I usually "randomize" the micrometer by giving it a quarter turn or so without looking between sights when I'm doing a set of lunars. That way I'm not as likely to be influenced by my previous sight.

    Amongst your sights:
    "36      Moon, Sun       09/20/2004 22:04:49     80.25643        80.24506        0.68
    36      Moon, Sun       09/20/2004 22:05:42     80.26952        80.25311        0.98
    36      Moon, Sun       09/20/2004 22:06:26     80.27711        80.25979        1.04
    36      Moon, Sun       09/20/2004 22:07:32     80.29761        80.26982        1.67
    36      Moon, Sun       09/20/2004 22:08:17     80.30030        80.27666        1.42
    36      Moon, Sun       09/20/2004 22:09:04     80.30809        80.28380        1.46"

    Hey, we were shooting lunars almost simultaneously. I did a set here in Chicago starting at 21:54:30 GMT and ending at 22:02:10. For what it's worth, here are my raw numbers:
    9-20-2004, Diversey Harbor, near 41d 56'N 87d 38'W. Temp=76F, Press=30.12", IC=-2.2'
    time     Sun-Moon lunar
    21:54:30   79d 55.2'
    21:56:20   79d 55.5'
    21:58:35   79d 56.5'
    21:59:40   79d 56.8'
    22:00:55   79d 57.3'
    22:02:10   79d 58.0'

    Could you post the original observed distances for your set "36"?

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
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