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Re: star-to-star distances
From: Fred Hebard
Date: 2004 Sep 29, 17:35 -0400
From: Fred Hebard
Date: 2004 Sep 29, 17:35 -0400
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