Jupiter and Galileo's Moons

This amazing photo of Jupiter was taken from Saturn! On February 8, 2007 Jupiter was 1.8 billion kilometres from our Cassini spacecraft. Two of the Galilean satellites are visible. When Galileo turned his telescope to the skies, he was amazed to discover Io, Europa, Ganymede and Callisto circling Jupiter. This provided evidence of objects circling something other than Earth, in defiance of Ptolemy's cosmology. Scientists of the time literally refused to peer in the telescope for fear of upsetting their world view.

“Here at Padua,” Galileo complained in a letter to Kepler, "is the principal professor of philosophy whom I have repeatedly and urgently requested to look at the moon and planets through my glass, which he pertinaciously refuses to do. Why are you not here? Whart shouts of laughter we should have at this glorious folly! And to hear the professor of philosophy at Pisa labouring before the Grand Duke with logical arguments, as if with magical incantations, to charm the new planets out of the sky.”

(Thanks Nigel, for reminding me of this quote, which I used part of in January 11 post.)

If that professor were alive today his magical incantations would no doubt include "dark energy" or whatever is fashionable and safe. He would try to prevent Galileo from speaking, publishing, or even having his observations considered. Unlike this writer, Galileo did not complete a university degree. That fact would be cited against him by today's elitists.

Despite his gap in formal education, Galileo was a fair scientist. He was willing to adjust his theories in accordance with new observations. His book "Dialogue on the Two Chief World Systems" gave equal time to opposing ideas. Some sinister folks spread rumour that the "Simplicio" character was a vague parody of the Pope. (Did they use e-mail?) Galileo was tried, forced to recant, and imprisoned for the last ten years of his life.

Below is a closer Cassini image of Jupiter, taken January 15, 2001 as the spacecraft completed its close flyby. Galilean moon Io is visible as a tiny crescent to the left. Four centuries later moons orbit planets and planets orbit the Sun just as Galileo believed. All follow elliptical orbits as Galileo's friend Kepler discovered. All follow paths controlled by Newton's gravity. The treatment given to Galileo is very relevant today.