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    Re: Lunars -Venus!
    From: Fred Hebard
    Date: 2004 Apr 25, 14:10 -0400

    I looked at your data and they were fairly consistent, not amazingly
    so, but good enough.  I am at a loss to explain why you would be
    measuring too small however.  My understanding, which I trust will be
    corrected by the list if wrong, is that most systematic sextant errors
    lead to a reading that is too large.  I usually "swing the arc,"
    rocking the body back and forth around the moon to ensure that I am
    measuring to the greatest extent of the bright limb.
    I do note that your index error is very large.  My understanding is
    that these should be adjusted when they greatly exceed about 1' of arc.
    On Apr 24, 2004, at 12:35 AM, Ken Muldrew wrote:
    > Last night the moon was in a cloud by the time I got out, but I did
    > get it on
    > Wednesday. I'm at latitude 51? 5'N and 114? 0.5'W.
    > Index error 8.3' on the arc.
    > Venus to the moon's lower limb
    > GMT     Distance
    > 3:13:10 15?58.2'
    > 3:11:50 15?57.3'
    > 3:13:10 15?57.0'
    > 3:14:30 15?56.0'
    > 3:15:20 15?56.2'
    > GMT is for Apr 22, the time was 9:mm:ss local time.
    > Sticking this into Arthur Pearson's webpage gave me a suprising -0.9'
    > error.
    > I also did Jupiter to the moon's LL
    > GMT     Distance
    > 3:17:10 99?7.8'
    > 3:20:50 99?6.5'
    > 3:21:10 99?6.2'
    > 3:22:30 99?4.2'
    > 3:24:20 99?4.0'
    > 3:26:00 99?3.4'
    > This was also a surprising -1.4' error in observation (substantially
    > more
    > in longitude).
    > Earlier in the day I tried getting a latitude from double altitudes of
    > the
    > sun. The artificial horizon that I built has a hood that has a bit of
    > a lip in
    > front of the pan. With the sun so low, I couldn't get a reflection
    > with the
    > hood on so I had to remove it. It was quite windy, so I had no chance
    > of
    > seeing one of the reflected limbs. Instead, I just tried to bring the
    > sun
    > over the centroid of the dancing green blob that was reflected off the
    > water. I only took a single reading at each time since it took about
    > 5-10
    > minutes just for that. At 5:54 PM local time (11:54PM GMT) I got a
    > reading of 50?37.4' for an altitude of 25?12.5' (same index error). At
    > 6:49:50PM I got a reading of 33?16.1' for an altitude of 16?35.1'.
    > Reducing this to a latitude gave me 51? 24' 41". Considering the
    > appalling accuracy of my readings, I was very surprised with the
    > accuracy of the result. Altitudes are certainly a lot more forgiving
    > than
    > lunars!
    > Ken Muldrew.

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