A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2020 Dec 12, 13:53 -0800
Last night the sky was clear. At about 2100 local time I could see Jupiter, Saturn, Mars, Sirius and a litte bit later Canopus. It wasn't the first time that I wished that I had a bubble sextant! I decided to measure the Saturn and Jupiter separation.
I had no difficulty seeing Jupiter and Saturn through the horizon glass. However I could not see Jupiter through the index glass. After a lot of experimenting I realised that when I took a sun sight with the AH I always used the clear part of the horizon glass. In all the time I have been taking sights I have never used the silvered part of the mirror. After more experimenting I found that I couds see Jupiter and Saturn and then, by moving the sextant slightly, the two images would disappear and a third image would come into view in the silvered mirror. Most importantly when I turned the tangent screw the image moved. The image was faint and I assumed that it was the doubly reflected Jupiter.
After some more experimenting I found I could see three images. As I turned the screw the two faint images suddenly overlapped. I quickly pulled my hand away from the screw, went inside and read the vernier. The results were:
12 December 2020 0900 UT (approximately).
Measurement 58' off the arc
IE 4' on the arc
Based on the above is it likely that I did measure the separation or is it a coincidence that the value is very close to the number Frank quoted? Any advice on how to take the measurement would be appreciated.