Observations As the Sun crossed through the plane of Saturn's rings during the nights of November 18 to 23, 1995, about 200 CCD images of Saturn's satellite and ring system were obtained in B, V, R, I, and the 890 nm methane band under sub-arcsecond seeing conditions. The observations were made using the Indiana University coronagraphic adaptor and re-imaging module on the 3.5m WIYN telescope at Kitt Peak National Observatory near Tucson, Arizona. The collaboration conducting the observations included I.U. astronomers Richard H. Durisen, R. Kent Honeycutt, John S. Jurcevic, and Robin Tripoli and NASA-Ames Research Center scientists H.C. (Luke) Dones and Mark W. Showalter. The WIYN Observatory is a joint facility of the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatories.
The above 120 second exposure with 0.8 arcsecond seeing was taken in the 890 nm methane band using a narrow filter (5.0 nm FWHM). The exposure was begun at about 4:06 Universal Time (UT) on November 22 (9:06 p.m. MST, November 21). A central mask about 25 arcseconds wide is used to reduce the scattered light from the disk of Saturn. North is to the top, and East is to the left. The Sun is on the opposite side of the rings from the Earth, and so the rings are a `negative' image of their usual appearance. The C Ring and Cassini's Division are bright while the A and B Rings are dark. This image clearly shows the small Saturnian moons Epimetheus (top of the East ansa, moving East), Prometheus (bottom of the East ansa, moving West), and Janus (bottom of the West ansa, moving West). This image confirms the suggestion from HST observations that Prometheus is about 30 minutes behind the position predicted on the basis of the pre-1995 ephemeris.
This pair of narrow-band 890 nm images were taken at 4:06 UT (top) and 4:17 UT (bottom) on November 22, 1995. Each exposure was 120 seconds long. Appreciable motion of the moons is evident in the eleven mintues between the exposures. The apparent dimming of Mimas (off the tip of the West ansa) in the bottom image is real. During this exposure, Mimas passed through the shadow of Tethys (West of Mimas).
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