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On Sep 29, 2004, at 4:30 PM, Alexandre Eremenko wrote:

> The results you report are of the same order of magnitude
> that I obtain. Which sextant did you use to obtain these results?
> The only obstacle to improving my results for the Sun
> seems to be the water motion in the art horizon because
> of the slightest vibration. My balcony floor vibrates when
> a dog is passing by on the ground under my balcony:-)
> But this can be fixed of course.
>
> But what about your older attempts with star-to-star distances?
> Were you successfull in determining instrument error?
>
> It seems to me that star-to-star distances should be MORE precise
> than Sun's altitude.
>
> Alex.

Alex,

Part of it is practice, lots of practice.  It's not as hard as learning
to play a piano, but it takes some proficiency.

I've been using a Cassens + Plath lately.  It seems to be very precise
and accurate, based upon my results with altitude shots; I don't have
many good data with it yet as I had trouble with a telescope.  If I
were on an unlimited budget and buying a new sextant today, I would buy
a Tamaya Spica.  I would like to sample some of the Russian sextants
too, but....

I don't know about the relative virtues of bronze versus aluminum for
sextants.  Aluminum was a pretty exotic material until about 100 years
ago, which my be why bronze is preferred.  Bronze also doesn't suffer
from electrolytic corrosion, which disfigures many an aluminum sextant.

Using Karo corn syrup reduces vibration.

You should be able to measure star-to-star distances very precisely.
Frank Reed seems to have, and I am sure he will chime in when he gets
back to the list, probably this weekend.  I haven't felt I was too
successful.

I haven't tried many star-to-star shots lately, as I have been doing
altitude shots instead.  I still have trouble getting stars to overlap
precisely, although some measurements were much more accurate and
precise than others.  The following data convinced me that my technique
was not sufficient.  Da-Do:sec is the seconds of arc between the
cleared observed distance and the calculated distance.  The last two
columns are the mean and standard deviation for these.  Note the widely
varying difference between Da-Do for objects between 25 and 33 degrees
apart.

Object1 Object2 degrees date    N(Da-Do)        Mean(Da-Do:sec) Std(Da-Do:sec)

Betelgeuse      Rigel   18      04/02/2003 00:59:18     3       17      20
Procyon Betelgeuse      25      01/13/2003 01:25:29     1       5       .
Sirius  Procyon 25      02/14/2003 04:57:12     3       -2      5
Sirius  Procyon 25      02/23/2003 22:24:40     4       30      20
Sirius  Betelgeuse      27      01/12/2003 03:46:39     2       -52     0
Betelgeuse      Pollux  33      02/23/2003 22:33:08     3       -45     11
Capella Betelgeuse      39      01/20/2003 23:21:31     3       2       10
Vega    Arcturus        59      07/16/2004 02:40:23     5       -13     59
Sirius  Capella 65      02/03/2003 02:09:00     13      -63     71
Sirius  Schedar 104     02/03/2003 04:09:56     4       -47     95

   

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