We recorded a rare mutual event of Mimas and Titan's shadow on the evening of November 9-10 1995 at the Vatican Advanced Technology Telescope (VATT: the Alice P. Lennon telescope and the Thomas J. Bannan facility) on Mt. Graham, Arizona, using a fast occultation CCD imaging system. The shadows of Rhea and Titan were also seen moving across the rings of Saturn itself. Our primary sequence of observations consist of six hundred images of the east ansa of Saturn's ring, each a three second exposure through the R filter, taken from 4:02 to 4:32 UT November 10. Saturn itself was masked from the CCD chip. Each pixel of the chip represented 0.3 arc- seconds. Seeing reached as good as 1.3 arc-seconds, but the focus of the VATT was not corrected during the run as the mirrors cooled, reducing the quality of some of the images. (With Gregorian optics, changes of as little as 5 microns in path length can significantly degrade the focus.) A passing weather front also provided challenges; though the telescope was remarkably stable even aimed into the wind, passing clouds degraded about 5-10% of our images. The predicted time of the event was 4:22:21 to 4:25:22 UT. A clear dip in brightness of Mimas occurs in our data between these times. Further analysis leading to a more precise timing of the shadow- Mimas event can give improved precision to the ephemeris of Mimas' orbit.
AAS/Division for Planetary Sciences Meeting Abstracts #28
- Pub Date:
- September 1996