Sky Talk November 2010: Jupiter Loses Belt & Gains Red Spot!

Magnificent Jupiter is at its best this month and has some real surprises in store for telescope users: it’s lost one of its two main equatorial belts, while its famed Great Red Spot is making a comeback after being barely visible for the past few years! All you need to see this for yourself is a clear night and a good-quality telescope, however small it may be.

Two of Jupiter’s best-known features: one has disappeared and the other reappeared! Even the smallest of telescopes at a magnification of 25x or so normally shows the planet straddled with two obvious brownish belts, known as the “North Equatorial Belt” and the “South Equatorial Belt.” When Jupiter emerged from conjunction with the Sun earlier this year, observers were shocked to see that the latter belt was all but gone! Seeing the giant planet with only one major belt is strange indeed. (There’s actually dozens of belts and bands and zones visible on the face of the planet — the larger the telescope and the better trained the eye, the more are seen!) This disappearing act has happened in the past and the belt is sure to return to prominence, but no one can say just when. So be sure to keep an eye on Jupiter!

Ever since the early days of the telescope, a huge cyclonic oval some 25,000 miles in length (the circumference of the Earth!) has been seen attached to the South Equatorial Belt and rotating rapidly with the planet itself. Often appearing reddish in hue in its “early days,” it was given the name the “Great Red Spot.” But over the centuries, it has from time-to-time faded and become difficult to see even in fair-sized telescopes. Its color also changes, affecting its visibility. It typically appears salmon pink or pale orange, but on rare occasions — as in the 1960s — a bright brick-red. I vividly remember seeing it easily back then in my little 60mm refractor.

During the past few years, the Red Spot has been decidedly difficult to spot! But it has made a comeback, and is becoming more obvious and colorful as time goes on. When on the side of Jupiter facing us (and given a steady night) it can even be seen in the Scientifics 60mm refractor with its 87x eyepiece (and normally both the major belts easily as well with its 35x eyepiece). The trick is knowing when to look, because it spends much of its time around the sides or back of the planet. Fortunately, Sky & Telescope provides a timetable of good visibility in both the magazine itself and on its site.

Needless to say, the larger telescopes in the Scientifics’ line will give much more detailed views of this strange object and the planet itself in general. They are also capable of showing the four bright Galilean satellites (those discovered by Galileo) as actual disks and not just jewel-like points of light circling Jupiter — orbiting worlds in their own right!

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of eight books on stargazing.