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Band on the Run

Week of March 9, 1998

Are you sick of hearing about El Nino yet? Me too. But it has made me think about weather in general, and on other planets specifically. It has also reminded me about an event I had almost forgotten about...


One of the first targets for anyone with a small telescope is Jupiter. It's bright, big and is a very nice target, even with the most modest of instruments. Even through a pair of binoculars, you can easily see the four large satellites of Jupiter, discovered by Galileo Galilee and imaged so amazingly by the Voyager and Galileo probes. The disk of Jupiter itself is easily resolved, and a small 'scope will reveal that the planet has three ghostly bands across its "surface". Those bands are actually immense hurricanes, fueled by Jupiter's interior heat and whipped into horizontal bands by the planet's fast rotation (Jupiter spins once every nine hours or so).

Galileo himself saw those bands, so we know they have been around for at least 400 years or so, and they are a staple of amateur astronomers' observations. Each is wider than the diameter of the Earth, and stretch clear across Jupiter's face. So you can imagine everyone's surprise when one of those bands disappeared, literally overnight.

Back in the early 90's I was observing the King of the Planets with a small 'scope, and immediately saw that something was amiss. I logged onto an astronomy chat group, and sure enough the place was abuzz with the news that one of the belts had disappeared. Much later, it was found that the belt had actually sunk a bit, and another layer of Jupiter's atmosphere had covered it up. It stayed that way for weeks, and then just as suddenly reappeared, looking no different than it had for the past four centuries. To the best of my knowledge, no one really knows just why the belt sank, or why it came back up.

I find this fascinating, and a bit familiar. El Nino is caused by a warming of the waters of the Pacific ocean, and no one knows what causes it. It has caused many deaths and tremendous property damage in the U.S., and has global ramifications, and let me stress here again that no one knows what causes it! We study the Earth as much as we can, but sometimes it's not enough. We study other planets, because their conditions are different, and it lets us see how different causes yield different effects. This particular soapbox of mine has my footprints permanently embedded in it, but this really does need to be reiterated to everyone: we study other planets to better understand ourselves. By looking outward, we can see farther inward. Astronomy is important, and I don't want anyone to forget it.

If you want to know more about Jupiter, you can start with my tour of the solar system page about it, and use the links I have there!

©2008 Phil Plait. All Rights Reserved.

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