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Rare Quadruple Transit
NASA's Hubble Space Telescope captured this image of of four moons of Saturn passing in front of their parent planet.
In the new 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. Saturn's rings will be
perfectly edge on to our line of sight on Aug. 10, 2009, and Sept. 4,
2009. Unfortunately, Saturn will be too close to the sun to be seen by
viewers on Earth at that time. 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.
The banded structure in Saturn's atmosphere is similar to Jupiter's.
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:
January 24, February 9, February 24, and March 12, although not all
events were visible from all locations on Earth.
These pictures were taken with the Wide Field and Planetary Camera 2 on
Feb. 24, 2009, when Saturn was roughly 1.25 billion kilometers (775
million miles) from Earth. Hubble can see details as small as 300
kilometers (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.
Image Credit: NASA/JPL/STSI
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