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Hubble Space Telescope Observation Plans


An Occultation by Saturn near the Ring-Plane Crossing of the Sun


On 20 - 21 November 1995, Saturn and its rings will occult GSC5249-01240, a star in the Hubble Space Telescope Guide Star Catalog. Amanda Bosh of Lowell Observatory and co-investigator Jim Elliot of MIT will utilize the Faint Object Spectrograph (FOS) to observe the occultation event. This event will occur near the stationary point in Saturn's orbit, so the apparent velocity of the event will be low. Serendipitously, it also occurs during the crossing of the Sun through Saturn's ring-plane. The Earth and Sun will be on opposite sides of the rings, so the rings will appear much darker than usual. Both of these circumstances contribute to the potential quality of data collected from the event.

During an occultation of a star by a planet, the planet passes between the star and the observer. The star then becomes a "probe" of the planet, allowing scientists to determine the temperature and composition of the occulting planet's atmosphere and the structure of its ring system. Such events led to the discovery of the Uranian ring system in 1977 and revealed Pluto's atmosphere structure in 1988. Because this event occurs near Saturn's stationary point the orbit of the HST will introduce a parallax effect, resulting in multiple passes of the star through Saturn's atmosphere and rings. Observing this event will:

  1. establish Saturn's atmospheric structure (in the 1 to 100 microbar region, which was inaccessible to Voyager instruments),
  2. determine how Saturn's atmospheric composition and temperature change with latitude, and
  3. probe the ring system for features of low optical depth (with spatial resolution better than 1 kilometer).

blue_dot.gif Postcript image of the expected occultation by Saturn and its rings.

saturn_home.gif Saturn Ring Plane Crossing Home Page