Rare Quadruple Transit
Date: 24 Feb 2009
NASA's Hubble Space Telescope captured this image of four moons of Saturn passing in front of their parent planet.
In this view, the giant orange moon Titan casts a large shadow onto Saturn's north polar hood. Below Titan, near the ring plane and to the left, is the moon Mimas, casting a much smaller shadow onto Saturn's equatorial cloud tops. Farther to the left, and off Saturn's disk, are the bright moons Dione and the fainter Enceladus.
These rare moon transits only happen when the tilt of Saturn's ring plane is nearly "edge on" as seen from Earth. This "ring plane crossing" occurs every 14 to 15 years. In 1995 to 1996, Hubble witnessed the ring plane crossing event as well as many moon transits, and even helped discover several new moons of Saturn.
Early 2009 was a favorable time for viewers with small telescopes to watch moon and shadow transits crossing the face of Saturn. Titan, Saturn's largest moon, crossed Saturn on four separate occasions: 24 January, 9 February, 24 February, and 12 March, although not all events were visible from all locations on Earth.
Hubble can see details as small as 300 km (190 miles) across on Saturn. The dark band running across the face of the planet slightly above the rings is the shadow of the rings cast on the planet.
Last Update: 22 Jun 2011 (AMB)