Dione is 698 miles (1,123 km) across, and its day side dominates the view on the right of the image. Mimas is on the left and measures 246 miles (396 km) across.
Lit terrain seen here is on the Saturn-facing side of Mimas and in the area between the trailing hemisphere and anti-Saturn side of Dione. North on both moons is rotated 20 degrees to the right of the top of the picture.
Image Credit: NASA/JPL