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Sky & Telescope's News Bulletin - May 19, 1995



This is the week that the rings of Saturn do a disappearing act. On May 22nd at about 5:15 Universal time, the planet's ring plane will sweep across the Earth for the first time since July 1980. Such spectacles occur twice during Saturn's 29.5-year circuit around the Sun. Even though mental geometry might suggest otherwise, we will actually experience three ring-plane crossings in the coming months due to the changing orbital geometry of Earth and Saturn. The other two will occur on the nights of August 10th and next February 11th. Right now backyard observers won't be able to see the rings, which have an estimated thickness of no more than about 100 meters. Some undulations do result from what are called vertical bending waves, but these add no more than 1 km or so to the overall thickness. However, you might glimpse the rings' shadow on the ball of Saturn itself, since the Sun is still on the north side of the ring plane by about 2.5 degrees.

Saturn rises only a few hours before dawn, so it's not particularly well placed for viewing. But note the planet's distinctly flattened shape -- its equatorial radius is about 10 percent larger than its polar radius. If you have a good-size telescope you might try to watch the planet's larger satellites play tag. Tethys, Dione, Rhea, and Titan are undergoing eclipses and occultations by Saturn and one another. For example, on the 26th at 14:47 Universal time, the bright moon Titan disappears into Saturn's shadow. On the 30th at 21:23 UT, Rhea occults neighboring Dione.

A complete observing guide to ring- crossing events begins on page 68 of SKY & TELESCOPE's May issue.

The News Bulletin is provided as a service to the amateur-astronomer community by SKY & TELESCOPE magazine. Electronic distribution of the News Bulletin is encouraged; however, this text may not be published without permission of Sky Publishing Corp. At the present time, the News Bulletin is not available via electronic mailing list.

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