just&ndash;space: Galilean moons Europa, Callisto, and Io pass in front of Jupiter. Photo of this rare triple-moon conjunction taken by the Hubble Space Telescope js

just–space: Galilean moons Europa, Callisto, and Io pass in front of Jupiter. Photo of this rare triple-moon conjunction taken by the Hubble Space Telescope js

just–space: Galilean moons Europa, Callisto, and Io pass in front of Jupiter.