Hubble Captures Rare Triple-Moon Conjunction
Firing off a string of action snapshots like a sports photographer at a NASCAR race, NASA’s Hubble Space Telescope captured the rare occurrence of three of Jupiter’s largest moons racing across the banded face of the gas-giant planet: Europa, Callisto, and Io.
These so-called Galilean moons, named after the 17th century scientist Galileo Galilei, who discovered them with a telescope, complete orbits around Jupiter with durations ranging from 2 days to 17 days. They can commonly be seen transiting the face of Jupiter and casting shadows onto its cloud tops. However, seeing three moons transiting the face of Jupiter at the same time is rare, occurring only once or twice a decade.
The Hubble image on the left shows the beginning of the event, which took place on January 24, 2015. From left to right, the moons Callisto and Io are above Jupiter’s cloud tops. The shadows from Europa, Callisto, and Io are strung out from left to right. Europa is not visible in this image.
More: Hubble Captures Rare Triple-Moon Conjunction - Astrobiology Magazine