TEAM OBSERVES RARE TRIPLE SHADOW ON JUPITER Our moon casts its shadow on Earth twice each year causing a solar eclipse. The next solar eclipse will be on February 26, 1998. The satellites of Jupiter cast their shadows more often onto Jupiter. However, only once or twice each century do three shadows meet in the same area. Erich Karkoschka of The University of Arizona and Scott Murrell of New Mexico State University observed such a rare event on Nov. 10, 1997 at the 24-inch (0.6 m) telescope of the New Mexico State University in Las Cruces. Five images of Jupiter show the progression of the event in a two-hour time period. In the first image, the black dot near the left edge is the shadow of the satellite Callisto. Slightly above it is the yellow-orange colored satellite Io in transit. In the second image, Io moving at a speed of 11 miles/second (17 km/s) has moved to the center of Jupiter's disk. Callisto and its shadow move at half of Io's speed. The shadow of Ganymede has appeared on the left side. Ganymede is the largest satellite in the solar system, about 50 percent larger than our moon or slightly less than half the size of the Earth. In the third image, the shadow of Io has appeared on the left side. The sun was shining from the right so that Io's shadow appears well to the left of Io. Ganymede and Callisto are further away from Jupiter and were outside the field of view when their shadows crossed the disk of Jupiter. In the fourth image, the three shadows have moved close together as Io's shadow is faster than Ganymede's which itself is faster than Callisto's. In the final image, the shadows of Io and Ganymede have merged. Io has finished its transit across the disk of Jupiter and is visible off the right limb of Jupiter. Io is much fainter than in the previous images since it is almost completely eclipsed by Ganymede. If the shadows of two object merge, the object closer to the sun is always eclipsing the other one. Jupiter displays several cloud features moving towards the right from image to images as Jupiter rotates once every 10 hours. The images were taken with visible and near-infrared filters. The color and intensity variations between different images are due to different filters used. The first image is in visible light and thus shows the colors similar as they appear to the human eye. Io reflects infrared light better than Jupiter. It appears very bright in the second and third images since these images mostly sample infrared light. During the event, it was cloudy over most of the south-western states. The observers recorded these images through holes in the clouds over Las Cruces. The atmospheric turbulence deteriorated during the event causing the later images to be less sharp than the first ones. Erich Karkoschka is a research associate at the Lunar and Planetary Lab at The University of Arizona in Tucson. He researches the atmospheres of the giant planets based on observations from the ground and from the Hubble Space Telescope. Observations and image processing presented here are not part of his supported research program. Scott Murrell is retired from the Department of Astronomy at the New Mexico State University. He brought the instrument into condition, and it worked perfectly during this event. Amy Simon of New Mexico State University provided calibration data. For More Information Contact: Erich Karkoschka Lunar and Planetary Lab, Univ. of Arizona Phone: (520) 621-3994 Tucson, AZ 85721-0092 Fax: (520) 621-4933 e-mail: erich@pirl.lpl.arizona.edu Image Files: ------------ A file containing all five images is available by anonymous ftp from: pirlftp.lpl.arizona.edu /erich/jupiter/imj.tiff There is also a gray-scale image: imjg.tiff The images can be viewed on the UA Science & Research web page: http://www.opi.arizona.edu/newsrel/science/science.htm