# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: A Jupiter Puzzle
From: Marcel Tschudin
Date: 2011 Oct 17, 13:04 +0300

You do understand that the only information that can be determined astronomically from the images is UT (GMT), right?

Yes

Information on the time zone follows from the time stamp on the images.

Yes, the time zone corresponding to the camera's clock but not necessarily to the one of the observer.

With some tests using my restricted possibilities I tried to find out how accurate one could determine UT with Jupiter's moons. The restricted possibilities consisted in the images which CalSky provides for the Jupiter moons for a given location and time, thus from the type of image which Greg showed at the beginning for his estimation but proceeding slightly more sophisticated. Assuming that the time stamps in the photos would be correct I measured the distance between the two inner moons (Io and Europe) parallel to a line between the two outer moons (Ganymede and Callisto) and determined the moment of conjuction of the two inner moons using a second order polynomial through the three data points. The distance between the two outer moons in the CalSky image served as a reference for scaling the photos. (As an example I attach the images of the photos and the corresponding CalSky simulation.) Here the obtained results for the selected locations:

Lon, Lat, Time of conjunction [UT]:

Photos:
7E, 48N, 23:32:09

CalSky simulation:
7E, 48N, 23:34:58
29E, 41N, 23:29:24
0E, 0N, 23:36:20
30E, 0N, 23:35:42
Mean: 23:34:06
+/- 00:03:11

Using the images of the CalSky simulation UT can be determined from the conjunction to about +/-3 minutes. I guess that a CN observation of a Jupiter's moon occultation could be more accurate for determining UT than this "photometric" measurement of the Io-Europe-conjunction.

Marcel

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