Question #30 – What are the Galilean moons?

Answer:

The Galilean moons are the four largest moons of Jupiter. They were discovered by astronomer Galileo Galilei in 1610 when he used his telescope to explore the night sky. The four moons - Io, Europa, Ganymede and Callisto - can be seen through a small telescope or a pair of binoculars that are firmly mounted.

You can learn more about the Galilean moons at Universe Today.

The Galilean moons shown to scale with Jupiter's Great Red Spot:
(top to bottom) Io, Europa, Ganymede, Callisto
Photo credit: NASA/JPL/DLR