January 30, 2009

Nearly 400 years ago, Italian astronomer Galileo Galilei constructed a tiny   astronomical telescope and looked at the night sky. He peered at the planet Jupiter, then a strange and mysterious object. Galileo discovered three faint dots around the planet and wondered what they might be.

Over the following year, Galileo observed Jupiter and these tiny pin-pricks of light. He discovered a fourth and saw that they were in motion around Jupiter. Could they be moons, other worlds in their own right? Galileo had discovered the first satellites circling around a planet other than our own. In future years they were named Io, Europa, Ganymede and Callisto. They are now known as the Galilean Satellites, in honour of the great scientist.

Galileo realized that these four moons were orbiting Jupiter. His observations cast doubt on the accepted view (at that time) that the Earth was the center of the Universe. Years later,  the Galilean moons would be used by science to support Copernicus’s theory of a heliocentric, sun-centered universe, which we now know is much closer to the truth.

With a small telescope or a pair of binoculars, you too can see Jupiter and its moons, much as Galileo did nearly 400 years ago. On a crisp and cloudless night, find a safe and dark location to look to the night sky. The best places to look at the sky are away from street lights. The best observing time for Jupiter this year is in the summer. Jupiter is bright during the month of August, making this a good time to view its moons.

Focus your telescope or binoculars on Jupiter and try to pick out the dots of light on either side. These are the moons, just as Galileo saw them! You can even track their positions over consecutive nights, as he did. Even if you don’t observe Jupiter and the Galilean moons during 2009, it’s still worth looking up on a starry night and remembering how, nearly 400 years ago, history was made by Galileo doing the same thing. 

Posted by: Seymour Simon

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