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Illinois hunting and fishing

Jan Sandberg
Jupiter and its four brightest moons are pictured using a 10 inch aperture telescope. The photo was taken by Jan Sandberg, Notice the bands on Jupiter.

Jupiter rules the southern sky

October 11, 2009 at 07:39 AM


Stealing the show in the southern evening sky this autumn is the gloriously bright planet Jupiter. Blazing at magnitude - 2.6, the fifth planet from the sun outshines all of the night stars and only Venus and the moon gleam brighter (and a rare fireball).

If you have even a small telescope, be certain to train it this way. You will at once see s small, white disc - the planet, and as many as four “stars” more or less in a row on either side. These are the four brightest moons of Jupiter, discovered by the great astronomer Galileo on January 7, 1610. Their names in order of distance from the planet are Io, Europa, Ganeymede and Callisto.

Figuring out which is which requires a good chart such as published in Sky and Telescope magazine and on their Web site, and undoubtedly in other sources. These charts show the moons as lines going around the planet as your eyes scan the column of dates, night to night. Each line is color coded to tell which moon is what.

Galileo didn’t have such a chart, of course, and had to do it the hard way. Hour by hour, and night by night, he tracked the positions of these star-like satellites that looked very much alike. As the moons moved in their orbits, each hour and each night they were seen in a different positions. Finally, he could tell what was what. You can do the same!

Today’s department store telescopes, almost universally maligned by experienced star watchers, are still superior to the crude, early instrument Galileo held up to the heavens.

Backyard telescopes of about 4 inches aperture or larger, with at least medium magnification and a good night with steady air, can reveal something of the transits of these moons as they cross the face of Jupiter. You may not be able to detect the moon itself against the bright planet, but what should be obvious is the ink-black round speck nearby, the shadow of the moon cast on Jupiter’s clouds. Indeed, this is a total solar eclipse in action, seen from above. Also visible, with even a small telescope, is the equally fascinating total eclipses of the Jovian (Jupiter) moons when they either disappear into the shadow of the great planet, or if missing the shadow, are seen gradually disappearing in back, or in front of the planet’s bright edge. These events are also listed by Sky and Telescope, and other sources.

One of the striking features of Jupiter is its bands. Can you imagine the music King Jupiter must enjoy! These bands are stripes of brown, yellow, orange and white that circle the planet and make up its perpetual covering of clouds. Among them the clouds sprout numerous spots, mostly oval, of varied shades and sizes, and a bounty of swirls and festoons. These features are always changing, although the principal bands are consistent.

Jupiter is 88,846 miles wide, more than 11 times the size of Earth. This is measured from the top of the cloud deck; the vast bulk is made up of mostly gas and liquid, with very little, if any, sold rocky core. In fact, astronomers have theorized that Jupiter should be classified somewhere between a planet and a star.

The brighter bands are referred to as zones, and the darker ones as belts. The colors represent different chemicals, which are churned in the interior by convection, cycled to the top. The bands are whipped by the enormously quick rotation of the planet, which spins once around in nine hours, 56 minutes.

The most famous spot is referred to as the Great Red Spot, a vast cyclone of reddish material that has been around for over 300 years. A small to medium sized telescope should be able to pick out at least two of the dark belts, and possibly the Red Spot, although the colors are difficult to discern in a small instrument.

Ability to see these features depend mostly on the stillness of the Earth’s atmosphere on the night you are watching as well as well earned experience, much the same that Galileo gathered. Steadily mounted binoculars are enough to show the moons, especially if not too close to the planet.

Last-quarter moon (the Earth’s moon!) is on Oct. 11.

The writer may be contacted at .(JavaScript must be enabled to view this email address).

Keep looking up!

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