Last week I told you how the rest of the summer is a wonderful time to watch Jupiter. It’s by far the brightest starlike object in the night time sky. No other star or planet is even close, and this month Jupiter is visible all night long, crossing the low southern skies.
It rises at sunset and sets at sunrise, and through even the smallest of telescopes or even binoculars, there’s much you can see on the largest planet in our solar system. Even with a pair of binoculars you can see Jupiter more clearly than Galileo did in 1610 with his homemade telescope.
As I told you last week, when you view Jupiter through a telescope, all you really see is a facade of atmosphere and cloud bands that completely encase the king of the solar system. Through a small telescope you can see at least some of the cloud bands, especially the two brighter ones that run on either side of Jupiter’s equator.
If our own atmospheric conditions are favorable you can see additional cloud bands, or even Jupiter’s Great Red Spot, which is actually like a giant hurricane, swirling for hundreds of years.
The best thing to do is watch Jupiter for as long as you can on any given night, as seeing conditions can rapidly change and you can get those wonderfully clear views of the Jovian giant.
Just as Galileo was, I know you’ll be fascinated by watching Jupiter’s four largest moons orbiting the planet in periods of two to 17 days. They look like tiny little stars on either side of Jupiter, and it’s fun seeing their positions change from night to night.
One of the things I really enjoy is watching one or more of the moons cross in front of the face of Jupiter, but that can be tricky, because they easily blend in with the cloud bands. I think it’s actually easier to see the shadows they cast on Jupiter’s cloud tops, because they’re visible as distinct contrasting black dots.
Again, Earth’s atmosphere has to cooperate, so patience is a big virtue when it comes to chasing moon shadows.
An essential tool for this is the Web site from the University of Maryland: www.astro.umd.edu/~lgm/astr120_fall97/jupiter.html, which you’ll want to put in your bookmarks. It’s a diagram of the positions of Jupiter’s moons, as well as the position of the Red Spot on the rapidly rotating planet. It also will tell you when one of the moons and its shadow is crossing Jupiter’s face.
The moons themselves will be depicted by a white dot across Jupiter’s face and their shadows will be black dots. Just set the time ahead to anytime in the future to see if any shadowy events are taking place that night or any other upcoming night. A word of caution: The displayed diagram is an upside down inverted view, which is helpful because most telescopes also give you an inverted image.
There’s another program you can use from Sky and Telescope Magazine that’s also useful but a little more complex. Just Google “Chasing the Moons of Jupiter,” and follow the steps at skyandtelescope.com.
The easiest moon shadows to see cross Jupiter are those of Ganymede and Callisto, Jupiter’s largest moons. Ganymede, at 3,269 miles wide, is even bigger than the planet Mercury. Jupiter’s smaller moons, Io and Europa, orbit closer to the big planet and are tougher to see. Consider them the big prize in moon shadow spotting.
Io and Europa are Jupiter’s most fascinating moons. Io is the most volcanic body of the solar system. Because of Jupiter’s tremendous gravity and tidal force, the rocks that make up the interior of Io are constantly rubbing against either other, generating massive interior friction and tremendous heat and resulting in the constant volcanoes of Io.
Io was dubbed the “pizza” planet, because when it was first photographed by space probes, the surface was a mix of red and yellow colors caused by all the volcanic activity. The Galileo spacecraft that orbited Jupiter for more than eight years charted a total of 120 volcanoes on Io.
Europa is even more fascinating, because its entire surface is a giant sheet of cracked ice. Once again, because of interior friction and Jupiter’s tidal forces, it’s thought to be warm enough to have a slushy ocean of water under that ice cover. Where there’s liquid water, maybe there’s some life. I doubt there are bass swimming around, but who knows what will be found if we ever auger our way through that ice.
Mike Lynch (www.lynchandthestars.com )is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis.
The Everett Astronomical Society welcomes new members and puts on public star parties. The Web site is members.tripod.com/everett_astronomy.
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