The Galilean Moons

Galilean Moons
Montage of Jupiter’s four Galilean moons, in a composite image comparing their sizes and the size of Jupiter. From top to bottom: Io, Europa, Ganymede, Callisto.

It’s such a pretty name, isn’t it? It makes you think of swashbuckling science fiction or the old Victorian fantasy fiction, the sort of stories that HG Wells wrote, or the pulp fiction of the 1920s.

I might have to see if there’s a story in that name…

However, the Galilean Moons are very real.

This day in 1610, Galileo Galilei spotted four of Jupiter’s moons. It’s no coincidence that the four he spotted were the four largest. Four hundred and four years ago, telescopes were in their infancy. Galileo made improvements to his telescope, and voila! He could see the moons distinctly.

That presented a bit of problem, because back in 1610, the scientists and the church (often, the same people) believed very much in the ascendency of Earth, and that the sun and the moon circled around Earth.

Galileo had already been insisting for several years that everything circled the sun, which gave him a heretical reputation.

The discovery of four moons that were clearly circling around Jupiter gave weight to Galileo’s theory which, of course, didn’t win him any popularity among the authorities of the day.

In fact, Galileo’s absolute certainty that the sun was the centre of the known universe resulted in him being was put on trial for heresy in 1632, and given house arrest for the rest of his natural life. He died ten years later, but not before he researched and wrote some of the most influential science books of the Renaissance.


Scroll to Top