Get Ready to Observe Jupiter

In my July column I reported that one of the main features of Jupiter, the South Equatorial Belt (SEB), was missing. For those of you not familiar with the morphology of Jupiter, this missing cloud belt is the one in which the Great Red Spot partially “resides” (it actually sits in the light-colored South Tropical Zone and “notches” into the brownish South Equatorial Belt north of it). The Spot continues unabated, but the view is quite strange compared to our “normal” view. It now appears to float within and above a deck of white ammonia clouds.

This phenomenon has occurred in the past, and the SEB eventually returned. Through an Internet service called Project Slooh, I recently (August 2) captured an image of Jupiter with the aid of a robotic telescope atop a mountain in the Canary Islands. (My tree-line has prevented me from viewing Jupiter from my home in Pascoag at a reasonable hour.) The missing belt was quite apparent.

While some of my colleagues have been observing and imaging Jupiter since January, until recently they had to do so during the early morning hours. I know many of you too need to wait for Jupiter to show itself at a more reasonable hour of the evening. Well, now’s the time to drag your telescopes out of the closet/garage/basement (or visit one of the local observatories) and focus in on the largest planet in our solar system. Before taking a first-hand look at how Jupiter currently appears, you may wish to refresh your memory on how prominent his cloud features looked before the SEB disappeared. Here is a web site you can access: http://science.nasa.gov/media/medialibrary/2010/05/19/loststripe_strip.jpg

If you do visit an observatory, the volunteers there will find Jupiter for you. However, if you have a telescope of any size, you most definitely will want to locate and view Jupiter on your own.

On September 1, Jupiter will rise above the due east horizon around 8:08 pm here in southern New England. Most of us do not have a “dead” horizon, so you must wait some time for the planet to rise higher into the sky. By 10:00 pm Jupiter will be 20 degrees above the horizon. You can’t miss it. It will be the brightest object in the sky. The higher it rises, the better it will look through a telescope, as long as the air is clear and steady.

Each night Jupiter will rise earlier and earlier, so by the 15th of September it will rise just after 7:00 pm, and by 10:00 pm it will be 30 degrees above the horizon. Plan your observing schedule using these dates and times.

Jupiter is a very beautiful planet to observe. Though it makes its closest approach to the Earth on September 20, it will still be about 367,000,000 miles from us. Despite this vast distance, Jupiter is a large world (you could fit 1,321 Earths within its volume) so even a small telescope will show the prominent cloud bands and its four primary moons.

I’m not sure what you will notice first when you observe Jupiter through a telescope. Perhaps it will be his Galilean moons or satellites, named in honor of Galileo Galilei who first observed them on January 7, 1610. Jupiter has four major moons (out of about 61 plus). They are named: Io, Europa, Ganymede and Callisto. Because they orbit around the planet in different paths, they are not all visible at the same time. In fact, during a rare two-hour period back in September, none of the four was visible from the Earth.

When multiple moons are present, they line up in the plane of Jupiter’s equator. As these satellites parade around Jupiter, many interesting events occur for us earth-bound astronomers to observe.

When a moon passes in front of Jupiter and casts a shadow onto the Jovian cloud tops, it is called a transit. Besides seeing the satellite’s shadow, you may also see the bright disk of the satellite traversing Jupiter’s clouds at the same time, though this event is more difficult to observe. A moon may also pass behind the planet, which is called an occultation. Jupiter’s shadow can even eclipse a satellite as well; gradually the moon will either blink out or reappear. Also, it’s fun to watch all four moons line up on one side of the planet. I love to watch Jupiter over an extended period of time during the course of one evening because the view is dynamically changing as you watch.

Next it’s time to look at Jupiter’s disk, the ball of the planet. Even a small telescope will reveal the more prominent dark bands/belts and lighter zones in Jupiter’s cloud tops. Though the Great Red Spot (GRS), an almost four hundred year old storm, is not as red as it once was many years ago, it should be very easy to see if it has rotated into view. Why? With the SEB covered by white ammonia clouds, the darker GRS stands out in stark contrast.

So get out there under a clear September sky and hone your observing skills on Jupiter.

But don’t forget, larger telescopes await your eyes every clear Saturday night at Seagrave Memorial Observatory (http:/www.theskyscrapers.org) on Peeptoad Road in North Scituate. Be sure to check the web site for scheduled open times and cancellations before venturing out for a visit. Also, when this column was being written during early August, the renovations at Ladd Observatory in Providence were still underway and the observatory remains closed. Once September arrives please check their web site frequently to look for a re-open date and time. As always there is no admission fee to either of these facilities on the public open nights.

Jupiter and a host of other fascinating astronomical objects await your gaze. Don’t let those photons go to waste!

Keep your eyes to the skies.