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

    Ken,
    
    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.
    
    Fred
    
    
    
    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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