The planet Jupiter is just making its appearance in the evening skies, and now dominates the southern horizon most of the night. For anyone who follows Jupiter closely, the giant planet presents a rather different face in 2007 than we've seen in recent years.
The two images above, made by D. L. Sharp with an 8-inch Newtonian, clearly show the changes which have taken place since this time last year.
All we ever see of Jupiter is the top of its thick gaseous atmosphere, and it's easy to forget that what we are seeing is clouds and that, as on our own planet, cloud patterns can change.
In recent years, the most obvious features have been two dark belts, known as the North Equatorial Belt and the South Equatorial Belt, with a lighter zone, the Equatorial Zone, in between, marking the planet's equator. Bright Tropical Zones appeared north and south of the two main belts. This is shown in the image on the left; north is at the top in these images. The result was a fairly symmetrical array of belts and zones relative to the equator.
Fast forward to 2007
The most striking change is that the southern half of the South Equatorial Belt has faded, changed from dark to light. At the same time, the normally bright Equatorial Zone has darkened, and the North Temperate Belt, to the north of the North Equatorial Belt has also darkened. The visual effect of this is that Jupiter's cloud belts have become noticeably asymmetrical: the whole northern half of the planet having become one dark complex belt, and the whole south of the planet becoming a broad bright zone.
These changes in the background colors of the belts and zones have had a striking effect on the appearance of Jupiter?s famous Great Red Spot. In recent years, the GRS has been buried in the dark hued southern component of the South Equatorial Belt, making it difficult to see in small telescopes due to the lack of contrast. In some years, it has actually been lighter than its background Belt, and has been visible only as a brighter area in a dark Belt, known as the Red Spot Hollow.
But now, in 2007, it is immersed in a broad white zone, and stands out clearly from its background, as can be seen in the image at right above. As a result, the Great Red Spot is easier to see in a small telescope than it has been for many years.
On the night of 2007 June 17/18 I was able to see it readily with my 100mm Orion ED refractor at 180x, which was next to impossible last year. No color was visible; that requires a larger aperture: on June 9/10 it appeared a pale salmon pink in my 11-inch Newtonian.
You can use Starry NightŪ to predict when the Great Red Spot will be close to Jupiter?s central meridian, the imaginary north-south line though the center of Jupiter's disk.
Starry NightŪ needs to know the current longitude of the Red Spot, since it drifts in longitude. It gets this information from a file in the Sky Data folder called JupiterGRS.txt. Mac users will need to control-click on their Starry NightŪ application icon, choose "Show Contents," and then drill down through Contents, Resources, and Sky Data to find this file.
If you have Starry NightŪ 6.0.0 or earlier, this file should be edited to contain the value 118.0. If you have Starry NightŪ 6.0.1 or higher, it should be 284.0.
With these values in the JupiterGRS.txt file, Starry NightŪ will depict the position of the Great Red Spot accurately so that you will know when best to observe it. Because of its improved visibility this year, give it a try!
Geoff has been a life-long telescope addict, and is active in many areas of visual observation; he is a moderator of the Yahoo "Talking Telescopes" group.