Last month, I featured Jupiter that was at its closest point to Earth in the last year. At the time, it was about 390 million miles from Earth. Since then, Jupiter and Earth have wandered a little farther away from each other, at least astronomically speaking, in their respective orbits around the sun.
Even though Jupiter's orbit is about 40 million more miles away than it was on New Year's Day, it's still by far the brightest star-like object in the evening sky right now. Not only that, it's in the middle of my favorite set of constellations, what I call "Orion and his gang." At the start of the evening, it's high in the sky almost due south against the backdrop constellation Gemini the Twins.
With 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 month in Starwatch, when you cast your telescope Jupiter, you'll easily see the disk of the big planet and maybe some of the cloud bands, especially the two brighter ones that run on either side of Jupiter's equator. If atmospheric conditions are favorable, you may also see additional cloud bands or even Jupiter's biggest red spot, which is actually like a super giant hurricane that's has been swirling for hundreds of years. Honestly though, the red spot isn't really all that red. It's more of a pale pink, but with the right conditions and a little work, you might spot it.
Not only can Earth's cloud cover effect how well you see details in Jupiter's clouds, but so can the high jet stream winds. The best thing to do is watch Jupiter for as long as you can on any given night because seeing conditions can rapidly change and you can get those wonderfully clear views of the Jovian giant.
Just like Galileo was, I know you'll also be fascinated by watching Jupiter's four largest moons orbiting the planet every two to 17 days. They look like tiny little stars on either side of Jupiter, and it's fun watching 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. The great thing is you don't need a very big telescope to see that. Again, Earth's atmosphere has to cooperate with what astronomers call good "seeing" conditions, so patience is a big virtue when it comes to chasing moon shadows.
An essential tool for this is the Jupiter's Moons Javascript Utility from Sky and Telescope Magazine. Check it out at
http://www.skyandtelescope.com/observing/objects/javascript/jupiter
You'll see a diagram of the positions of Jupiter's moons. It will also tell you when one of the moons and its shadow is crossing Jupiter's face. Just set the time ahead to any time in the future to see if any shadowy events are taking place that night or any other upcoming night. The displayed diagram is a direct view, but most telescopes also give you an inverted image so you might want to set utility to the inverted view of Jupiter and its moons to make it less confusing.
There's another great tool to help you find Jupiter's great red spot while the largest planet in our solar system rotates on its axis in only about ten hours, much faster than the Earth's rotation. You can find it at http://www.skyandtelescope.com/observing/objects/javascript/3304091.html
There are also many apps you can get on smart phones to help you determine the positions of Jupiter's moons as well as the position of the red spot, and they're all reasonably priced.
The easiest moon shadows to see cross Jupiter are those of Ganymede and Callisto, Jupiter's largest moons. In fact, Ganymede, at 3,269 miles wide, is even bigger than the planet Mercury. These larger moons make larger shadows. 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.
Coincidentally, Io and Europa are Jupiter's most fascinating moons. Io is without a doubt 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.
Europa in my astronomical view is even more fascinating because its entire surface is a giant sheet of cracked ice. Once again because of Jupiter's tidal forces and interior friction, it's thought to be warm enough to have a slushy ocean of water under that ice cover. Where there's liquid water, who knows, 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.
Enjoy watching Jupiter's moons and their shadows. It's challenging and a lot of fun.
(Lynch is an amateur astronomer and author of the book, "Stars, a Month by Month Tour of the Constellations." Contact him at mikewlynch@comcast.net.)