Wednesday, July 15, 2009

Galilean moons

That bright object east in the evening sky is Jupiter. If you have a pair of normal binos, take a peek at it. Depending on the timeframe you can usually see 4 or so star-like objects near Jupiter; they are the moons Io, Europa, Ganymede, and Callisto.

Right now there are two on the left side and two on the right side of Jupiter.

Galileo was the first person to describe their periodicity around Jupiter. Check out his notes and drawings of the moons in the image.

Side effect: Before the invention of an effective seagoing clock mechanism sailors could use the position of the moons to tell what time it was. And if you new what time it was you could, using a bit of declination, deduce your longitude.

But the major news was that Galileo was eating forbidden fruit and realized it. The official position was that all heavenly bodies (including the sun) orbited the earth, as befits God's creation. But Jupiterian moons demonstratably orbited Jupiter. This broke the universe, or at least the theological understanding of how the universe worked.

That kind of shift in human understanding is found over and over again in Renaissance studies. Man sets himself on a path that will eventually lead to a rigorous scientific methodology.

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