Sunday, October 30, 2011

What Galileo Saw

Last night (October 29), Jupiter was in opposition to the Earth, which means that it is exactly opposite the sun, and that it is as close as it is going to be this year. I do not know if it is the closest that it has ever been to the Earth, but it is close enough that even an inexpensive telescope will allow you to see its banded clouds. I have not yet seen the red spot, however. Jupiter is easily the brightest object in the sky after sunset. It rises about 8:30 local time.

The most amazing thing about looking at Jupiter is that you can see its moons. If you look at it on successive nights, you will see that the moons move quite rapidly—not rapidly enough to see, but enough that they are in strikingly different conformations each night. It was not just the moons, but the movement of the moons, that Galileo observed, and which led him to understand that Jupiter was a planet with its own moons. Jupiter was not just a bright light on a sphere that turned around the Earth. When Galileo made these observations, the medieval view of the cosmos fell apart, and those whose power depended on the medieval mindset (the Church) reacted with ferocity. The outcome of the Church’s attack on Galileo is well known.

You can get out a telescope and observe the very thing that got Galileo in trouble and changed the human view of the cosmos.

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