You don’t see it, but it’s there
Dione and Mimas by Cassini. Credit: NASA/JPL-Caltech/Space Science Institute
The bigger moon that filled the view is one of Saturn’s many moons Dione. The night side of Dione blended into the dark space beyond and it seems like there is nothing there. But with the help of the smaller moon Mimas peeking out from behind, we can see the edge of Dione, and realised that there is something there after all.