Night Flight to the Stars

Activity 4D: The Case of the Disappearing Rings

The famous ringed planet Saturn appears almost ringless for much of 1995 and early 1996. Every 15 years the Earth passes through the ring plane of Saturn and the planet's thin rings seem to disappear. The rings were edge-on in May and August of 1995 and have a slight tilt in the Fall.

Compare the two Hubble Space Telescope photographs of Saturn. In Dec. 1994, the Earth was above the lit face of the rings. The rings are seen edge-on in May, 1995. Saturn's moons Tethys and Dione can be seen in the ring plane to the left of Saturn.

Saturn's rings are composed of billions of particles--largely water ice--that range in size from tiny crystals to chunks the size of houses and school buses. Considering what the rings are made of and their size as shown above, predict how much lower the infrared brightness of Saturn will be in October 1995--compared with a ready when the rings were fully displayed. Record any reports about Saturn's brightness from the KAO astronomers.

Still more exciting is the opportunity to find and study Saturn's large moon Titan. Titan is almost as large as Ganymede and Callisto of the Jupiter system. The cooler Titan, however, has an atmosphere, mostly of nitrogen with various hydrocarbons mixed in. (The Earth's atmosphere is also predominantly nitrogen.) Titan's atmosphere is so thick that the Voyager spacecraft flying by Saturn could not see Titan's surface. Liquid ammonia and natural gas could exist on Titan.

At the time of the KAO observations, Titan will be 3 arc minutes west of Saturn. Saturn's rings will be 43 arc seconds in diameter and the planet will be 19 arc seconds wide.

KAO Corner

  • Do you think that Titan will be brighter or fainter than Jupiter's moons when seen from the KAO? __________ Give a reason for your answer.
  • Titan will be observed at night while Jupiter's moons are imaged during the daytime. Do you think this will make a difference? __________
  • How many arc seconds will separate Titan and Saturn? __________
  • On another sheet of paper, make a drawing showing Saturn, its rings, and Titan to scale.
  • Use your drawing to explain how the KAO telescope operator should move the telescope once Saturn has been centered on the view screen. The field of the KAO infrared camera is 2 arc minutes. Can the camera make an image of Titan without getting any stray light from the rings? __________

This page was created by Daniel Helfman, a junior at Mission San Jose High School in Fremont, CA.

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