A new Hubble photograph captured a rare alignment of four
of Saturn's moons lining up in front of their planet.
The snapshot, taken on Feb. 24 with the NASA/European
Space Agency (ESA) Hubble Space Telescope, shows the moons transiting in front
of Saturn. The moons, from far left to right, are the white icy moons Enceladus
and Dione, the large orange moon Titan, and icy Mimas. Due to the angle of the
Sun, they are each preceded by their own shadow.
These rare moon
transits only happen when the tilt of Saturn's ring plane is nearly
"edge on" as seen from the Earth. Saturn's rings will be perfectly edge
on to our line of sight on Aug. 10 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 14-15 years. In 1995-96 Hubble
witnessed the previous ring plane crossing, as well as many moon transits, and
helped to 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: Jan.
24, Feb. 9, Feb. 24 and March 12, although not all events were visible from all
locations on Earth.
Italian Galileo Galilei — often referred to as the father
of astronomy — was the first to observe Saturn through a telescope in 1610.
Dutch mathematician and astronomer Christian Huygens discovered Titan in 1655
and, 350 years later, the ESA probe named for him touched down on Titan (on Jan.
14, 2005), giving the world its first views of the surface of the mysterious,
icy world. Giovanni Domenico Cassini, a French/Italian astronomer, discovered
Dione (in addition to others) and the German-born Englishman, William Herschel,
discovered Mimas and Enceladus.
These pictures were taken with Hubble's Wide Field
Planetary Camera 2 when Saturn was at a distance of roughly 780 million miles (1.25
billion kilometers) from Earth. Hubble can see details as small as 190 miles (300
kilometers) 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.
advertisement
