The Moons of Jupiter

There was a time many years ago when the brilliant white star that stands out in the night for much of the year was, to me just that, a big star. One day my Dad told me it was the planet Jupiter. But it was years before I ventured to pick up a pair of field binoculars and look for myself. I can remember the moment, a dark night in Devon. There to my astonishment was not just the clear bright disc of the planet itself but four smaller bright dots lying in a line to the right. Io, Europa, Ganymede, and Callisto the Galilean moons of Jupiter. It's one of the easiest and most thrilling astronomical sites to view. But it has had profound consequences to how we view our place in the universe.

Four hundred years before I picked up my cheap binoculars a great Italian Galileo Galilea had the same thought. Except his spy glass was not cheap, it had been crafted at huge expense by his own Venetian workshop. It was in fact the first true telescope. Designed not for gazing at the cosmos, but spotting approaching enemy ships. One night Galileo must have had the same urge that I felt in Devon. He pointed his telescope at Jupiter. He became the first person to see the moons of Jupiter. Galileo was a man of great thinking, he understood the consequences of what he had seen. If small worlds orbited Jupiter, was it not likely that the Earth orbited something too? It did. The sun.  This view (the heliocentric view- meaning sun in the middle, as opposed to geocentric view - meaning earth in the middle) seems so obvious to us that it is hard to believe anybody ever thought anything else. But geocentricity is quite logical. The Earth doesn't look like it's moving, and to the observer absolutely everything in the sky clearly is moving.

To the sixteenth century establishment heliocentricity was a radical, blasphemous thought. So much so that it nearly cost Galileo his life. The church shuddered at the consequences . Its belief was that the Earth was at the centre not just of the solar system but of the whole universe. Everything revolved around it. To believe anything else argued for a demotion in the importance of the Earth, ambiguity over god's place in the it, and of course it meant the church wasn't quite so important after all. Heresy!

Galileo avoided execution by retracting the conclusions from what he saw. The agreed line was that although Jupiter may or may not have moons orbiting it, everything still orbited the Earth . Others weren't so lucky Giordano Bruno the Italian friar and astronomer was burned at the stake for his views which were similar to Galileo's although he appears to have annoyed the church in a number of other ways too. All mention of the Heliocentric universe was banned by the catholic church until 1822. Astonishingly it was not until 1992 that pope John Paul II finally accepted that Galileo was right. In 2000 one of John Paul's cardinals, Angelo Sodano expressed regret of the burning of Bruno. It was, he said a "sad episode in newer christian history"  The consequences of picking up a telescope have never been greater.