This animation, constructed from Hubble Space Telescope images, shows a rare alignment of three of Jupiter's largest moons across the planet's face. The moons are Io, Ganymede and Callisto. An alignment like this only happens about once or twice per decade.
In this video you can only see two of the moons, but the shadows of all three are clearly visible on Jupiter's surface. The first moon to come into view is Ganymede (blue), followed by Io (white). Callisto is out of frame to the right. The black dots on Jupiter are the shadows.
Credit: NASA, ESA