Astronomy Picture Of the Day (APOD)Iapetus: Saturn's Disappearing Moon
Iapetus has an unusual surface, one half of which is very dark, the other half very light. This caused it's discoverer Cassini to remark that Iapetus could only be seen when on one side of Saturn but not the other. The reason for the difference between hemispheres is presently unknown.
Rhea: Saturn's Second Largest Moon
Rhea is the second largest moon of Saturn, behind Titan, and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea's rotation and orbit are locked together (just like Earth's Moon) so that one side always faces Saturn.
Jupiter, Io, and Ganymede's Shadow
Jupiter, the solar system's largest planet, is seen here next to Io, its closest Galilean moon. On the cloud tops of Jupiter near the left edge of the picture can be seen a dark circular spot which is caused by the shadow of Jupiter's largest moon Ganymede.
HH-47 Star Jet
The star masked by a dust cloud at the left of the above photo is expelling an energetic beam of charged particles into interstellar space. This jet, moving from left to right, has burrowed through much interstellar material, and now expands out into the interstellar space.
LMC Star Clouds
Pictured above are clouds of young stars forming an arc in the nearby Large Magellanic Cloud, the nearest galaxy to the our Milky Way Galaxy. These stars are situated in a star forming region known as N 51.
Dione's Lagrange Moon Helene
Saturn's moon Helene is very unusual in that it circles Saturn near the orbit of a bigger moon: Dione. Helene is situated in what is called a "Lagrange point" of Dione - a place of stability created by Dione's gravity.
Saturn's Moon Dione
Dione, one of Saturn's larger moons, is remarkable for its bright surface streaks. These streaks run across some of Dione's many craters, which indicate that the process which created the streaks occurred later than the process which created the craters.
Apollo 12 Visits Surveyor 3
Apollo 12 was the second mission to land humans on the Moon. The landing site was picked to be near the location of Surveyor 3, a robot spacecraft that had landed on the moon three years earlier. Pictured above, Apollo 12 astronauts Conrad and Bean retrieve parts from the Surveyor.
Apollo 12's Lunar Module Descends
A few months after Apollo 11's historic Moon landing, Apollo 12 with commander Charles Conrad Jr., Command Module pilot Richard Gordan, and Lunar Module pilot Alan Bean returned for more geographic and scientific exploration.
Dark Bok Globules in IC 2944
The dark spots in the above picture are not photographic defects but an unusual type of interstellar cloud known as a Bok globule. Bok globules, named after astronomer Bart Bok who studied them extensively, are small dark clouds made of gas and dust that are typically condensing to form a star or stars.