The Moons of Jupiter

October 23, 2009

jupiter-galilean-moonsAs Jupiter lingers in Capricorn this month, why not take a few minutes to step outside into the crisp fall air (or warm spring air if you’re south of the equator) and take a look at the big planet’s four largest moons?

“Oh, I’ve seen them many times before”, you say. “They’re getting a little boring to look at.”

Boring? Come now. When you begin to tire of the beautiful sights in the night sky, it’s time to fire up your imagination. As you look at Jupiter’s four largest moons, Io, Europa, Ganymede and Callisto, you might consider all the areas of art and science these four moons have influenced over the centuries.

For example…

1. Esthetics
The tiny pinpricks of light lined up with the bands of their giant home planet are in themselves a beautiful sight, even in the most modest pair of binoculars. Were it not for the overwhelming brilliance of Jupiter itself, you could easily see all four of these moons lined up like little stars.

Here’s a strikingly beautiful photo of our own moon and Jupiter. In this case, clouds passing in front of our moon allowed the exposure of the camera to be set to capture this scene. You can learn how to take photographs like this yourself here.

2. Drama
The moons of Jupiter move constantly, revealing almost nightly displays of shadows, occultations, and disappearances. When all 4 large moons disappeared from view one by one in early September, even though I was dead tired and desperately wanted to sleep… I couldn’t take my eye off of this show. It was absolutely gripping. And I’ve been doing this for more than thirty years.

3. Physics
The graceful rhythmic motion of the moons is governed by the laws of Newtonian gravitation. But observations of the moons also helped astronomers in the 17th century to understand that light moved at a finite speed, and helped them determine that speed fairly accurately. This was a totally accidental discovery.

4. History
The four bright moons of Jupiter were discovered by Galileo almost exactly 400 years ago. To celebrate this discovery and others by Galileo, this year was named the International Year of Astronomy.

But Galileo’s discoveries got him into hot water with the church. Despite the plain evidence in Galileo’s telescope, which they were invited to look through, church leaders compelled Galileo upon threat of excommunication and painful death to renounce his views that the Earth moved around the sun, as Jupiter’s moons revolved around the giant planet.

It’s a small mark of human advancement that, in some parts of the world, a scientist can oppose deeply held beliefs without having his life destroyed. Mostly.

5. Literature
We’ve already covered Arthur Clarke’s proposal of life under the thick ice of Europa in his science-fiction novel 2010.

And Canadian author Alice Munro named one of her lovely short stories “The Moons of Jupiter”, in which the main character had a small personal revelation while learning about the moons during a show at a planetarium.

Truth is, it’s hard not experience some personal insight while stargazing. If you just keep your mind open, and use a little imagination.

You just have to get outside and look up.

Posted in Celestial Objects, Solar System Observing



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