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On Sep 24, 2004, at 9:35 PM, Frank Reed wrote:

> 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

That's pretty cool we were shooting at close to the same time.  It
looks like you may have planned your shoot rather carefully, as it was
right when both bodies were at maximum mutual altitude, about 20
degrees.

When I said I "reset" I twisted the micrometer as you describe for
"randomize"

Here are my raw data.

Index error, 33 seconds, off the arc (it was off, so I added it to the
observed distance).
Presumed pressure 28.0".  Temp 70F. 36*46.8'N 81*50.7'W.  Sun-Moon,
both bodies touching on near side.

time    degrees minutes
09/20/2004 22:04:49     79      52.5
09/20/2004 22:05:42     79      53.1
09/20/2004 22:06:26     79      53.4
09/20/2004 22:07:32     79      54.4
09/20/2004 22:08:17     79      54.4
09/20/2004 22:09:04     79      54.7

I also reduced your data, which made me rather jealous!  Here they are:

ClrdD   CalcD   time            lunar   delarc'
80.15185        80.15086        21:54:30        21:54:36        0.1
80.16221        80.16762        21:56:20        21:55:44        -0.3
80.18556        80.18820        21:58:35        21:58:17        -0.2
80.19380        80.19811        21:59:40        21:59:11        -0.3
80.20626        80.20951        22:00:55        22:00:33        -0.2
80.22167        80.22090        22:02:10        22:02:15        0.0

   

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