The Moon
The Moon is Earth’s only natural satellite—a rocky, cratered body about one‑quarter the diameter of Earth, orbiting at an average distance of approximately 384,400 km. It influences tides, stabilizes Earth’s axial tilt, and was formed about 4.5 billion years ago following a collision between Earth and a Mars-sized object.
Source: science.nasa.gov
APODs including "The Moon"
Unusual Cratering on Saturn's Dione
01/08/2007
Why does one half of Dione have more craters than the other? Start with the fact that Saturn's moon Dione always has one side that faces Saturn, and always has one side that faces away. This is similar to Earth's Moon. This tidal locking means that one side of Dione always leads as the moon progresses in its orbit, while the other side always trails. Dione should therefore have undergone a significant amount of impacts on its leading half. But the current leading half of Dione is less cratered than the trailing half! A possible explanation is that some impacts were so large they spun Dione, sometimes changing the part that suffered the highest impact rate before the moon's spin again became locked. Pictured above, it is the top part of Dione that appears significantly more cratered than the bottom half.