MOON DANCE:

The Hubble Space Telescope captured four of Saturn's moons transiting, or passing in front of their planet, at once. In this February image from Hubble's Wide Field Planetary Camera 2, Saturn's largest moon, Titan, and its shadow are plainly visible across the ringed planet's northern hemisphere. The much smaller Mimas is barely visible as a whitish dot below and to the left of Titan (just above the rings), but can be found next to the more apparent dark shadow it casts across the gas giant. To the left of the image is Dione, which appears to hover above the rings, and Enceladus, the tiny speck at the rings' edge. Hubble's view was made possible by the fact that the plane of Saturn's rings aligns with our line of sight in 2009—the rings will be perfectly "edge-on" on September 4. (At that time, however, Saturn's position relative to the sun will largely preclude observation from Earth.) This alignment takes place every 15 years or so as Saturn makes its 29.5-year orbit around the sun and has not occurred since 1995–1996.