The Galilean moons may sometimes cross the disc of Jupiter in an event called transit. The satellite (white dot) is usually followed by the shadow (black dot) it casts on Jupiter. In this photo, Jupiter’s moon Io is already exiting, with its shadow still on the disc of the planet. Image taken on November 9, 2011 with a 4-inch f/9 refractor and a Logitech 4000 web camera.
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