As regards short eclipses of ISS, my understanding is that they can only occur just before and after the time when ISS is continually sunlit. This was the case between 23:33 UTC on 31.05. (i.e. 31 May) and 21:22 UTC on 04.06. (i.e. 4 June). Just before this period, there was an eclipse of 2m31s at 23:20:25 UTC on 31 May, and the first eclipse after the continuous illumination occurred at 21:21:32 on 4 June for a duration of 2m 25. Since then, the eclipses have become longer and longer. The observation of eclipses a few minutes long requires that the observer is located where both events, entry into and exit from the eclipse are visible. Considering that the visible fraction of a pass seldom exceeds 6 minutes or so (depending on local horizon circumstances), one has to be located at a place where the satellite passes close to the zenith. In addition, the longitude has to be such that both events occur whilst the satellite is above the horizon. This limits considerably the locations from which short eclipses in the order of a few minutes can be observed. My definition of "eclipse" is somewhat simplistic: if the line satellite-Sun intersects the Earth, the satellite is in darkness, otherwise it is sunlit. The Earth is assumed to be a perfect sphere, and the Sun is a pointlike source. This approach does not take into account the partial phase of the "eclipse". I am working on a more sophisticated approach, but the mathematics are quite complex. BTW: the time when a satellite is in continuous sunlight occurs when the right ascension of its ascending node (RAAN) minus the RA of the Sun are close to 90 degrees (for the northern hemisphere) AND when the declination of the Sun exceeds a certain value which is a function of the satellite's inclination and its orbital height. The phenomenon of short eclipses should occur not only for ISS but for many other satellites as well. Bruno Tilgner Saint-Cloud, France 48.85N 2.02E UTC+2 ISS etait illuminee sans interruption entre le 31.05 23:33 UT et le 04.06 21:22 UT. Juste avant et apres cette periode les eclipses etaient tres courtes. La derniere avait lieu le 31.05 a 23:20:25 pour une duree de 2m31s, et la premiere le 04.06 a 21:21:32 UT pour une duree de 2m25s. Depuis, les eclipses sont devenues plus longues, par exemple 7m06s le 05.06. ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
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