Jupiter, February 26, 2003, 07:33 UT. This image was obtained about one week before opposition. Io is to the right. 203 mm f/7 newtonian with ToUcam Pro Webcam @f/35. 

            Jupiter is the largest planet, a gas giant with a banded pattern of clouds. The clouds show a subtle and ever changing variety of colors and patterns. In many ways, it is the most rewarding planet for amateurs to observe

    My first telescope was an Edmund’s 3” Newtonian. Though this telescope easily showed Jupiter's Galilean satellites, I was never able to detect cloud bands with it. My next scope was a Criterion 6” Newtonian. With it, not only was I able to detect banding, but I was finally able to discern some of the delicate colors of Jupiters clouds. This allowed views of the famed Great Red Spot, the hurricane like storm that has been raging for several centuries at least. For me the most inspiring sights involve the transits of the moons and their ink-black shadows across the cloud tops. The realization that each of the Jovian worlds is approximately the size of our own Moon or larger and yet each is dwarfed by the massive Jupiter helps put things into perspective.

The shadows of Io (smaller of the two shadows) and Ganymede, January 8, 2001. 203 mm f/7 newtonian and PC-23C video camera with wratten #25 filter.

Jupiter's Atmosphere

    Jupiter is possessed by a complex weather system. Unlike the Earth and other terrestrial planets, the atmosphere of Jupiter is very deep extending to a depth of thousands of kilometers. Jupiter's interior acts like a fluid. In many respects, therefore, Jupiter more closely  resembles a star than a terrestrial planet. Unfortunately, we are unable to observe the motions deep within Jupiter's interior. We can only observe Jupiter's cloud tops. These consist of alternating light and dark bands that parallel the equator. They are composed of winds that that flow east or west. The dark bands represent areas of rising, moist air. The dark Equatorial Bands that straddle the equator often contain large convective storms. The Galileo spacecraft revealed that these storms are marked by intense lightning activity. The lighter zones represent areas where dry descending air predominates. Recent modeling suggests that the alternating flows of air are ultimately driven by cyclonic flow around these convective centers. In this way, small scale "atmospheric whirpools" provide the force that spins the bands. It is not known if the surface cloud patterns reflect deep atmospheric circulation. However, the enery to drive this circulation is thought to originate largely from within Jupiter itself rather than from the Sun.

    More detailed information about Jovian atmospheric activity can be found at Jovian Activity and Nomenclature, a website maintained by Damian Peach

    The Equatorial Zone (EZ) is an area of eastward blowing winds. Dark, bluish festoons project from the northern edge of the zone and are sheered into diagonal plumes across the equator. In infrared light, these plumes are bright indicating that they are hot relative to the surrounding cloud deck. These were, until recently, thought to be analogous to eruptive plumes by some workers. However, the Galileo Probe plunged an area near the center of a large fastoon and found, contrary to expectations, very little water vapor. Instead, The EZ is now understood to represent an area of dry descending air.  The blue festoons are openings in the high altitude cloud deck that allow observers to peak into the hot atmosphere far below.

    The light reflected from Jupiter's cloud tops contain a wealth of information about their depth and temperature. In general, features that are dark in red light (that is, blue) are generally believed to be from deeper in the Jovian atmosphere. Blue light images generally highlight the features from the upper Jovian atmosphere.

Jupiter as seen in raw (unprocessed), and separated into red, green, and blue channels, and as the final processed rgb image. These images were obtained January 9, 2002 with an 8" f/7 newtonian and an Intel PC CS430 (Intel Pro Video PC Camera). 

    Jupiter is composed of a witch's brew of chemicles. It is largely of hydrogen and helium. There are lesser amounts of other elements, nearly in the same relative abundances as are found in the Sun. The white clouds are composed of ammonia ice (NH₃) that freezes out of Jupiter's atmosphere at high altitudes. Darker clouds probably contain complex organic particles that form a smog. Sulfur and other elements such as phosphorous might also be a coloring agent.

Jupiter with its Great Red Spot, February 15, 2004, 06:48 UT. 203 mm f/7 newtonian with ToUcam Pro Webcam @f/35.

    One of the continuing mysteries of Jupiter's weather is why there is a strong asymmetry in air circulation patterns. Jupiter's southern hemisphere contains numerous cyclonic storms situated at about 40 degrees latitude. The larges of these is the Great Red Spot (GRS). This is a large storm system that is very persistent, probably continuing for over 300 years! The GRS represents a spiraling column that rises high above the surrounding cloud deck. The clouds at this height are extremely cold and therefore the GRS is dark in infrared light. The red coloration may be due to phosphorous. It is possible that gases are rapidly brought to the surface from a great depth before they can be destroyed. 

    The polar regions experience strong auroras. These are created as ionized particles captured from the solar wind and from Jupiter's neighborhood by Jupiter's intense magnetic field. These particles are channeled into and collide with the upper atmosphere of the Jupiter's polar regions. The aurora may drive chemical reactions to create the distinctive polar darkening. The polar regions show less banding and have a mottled appearance. High resolution images obtained from the Cassini spacecraft show an abundance of vortex-type motion in this area.

The Jovian System

     Each of the Jovian moons shows a disk and is a world in its own right, though surface markings of Ganymede and Io are only barely visible in amateur scopes. Ganymede shows high contrast surface features including the dark Galileo Regio to scopes as small as 6” and definitely in 10” and larger. This on a disk that never exceeds about 2 arcseconds in diameter. Io shows a darker equatorial region in scopes as small as 10” under excellent conditions. The moons can be readily distinguished visually by size and color, and differences in size and brightness can be detected in video images taken with my 8.”

    Imaging Jupiter is relatively easy because it is bright and large. However, its fast rotation requires that frames that are to be combined from video must be restricted to only a few minutes, preferably less than 2. Also, Jupiter presents a "soft" target that is difficult to focus on. Some instead focus on the nearby moons. I especially like to use the shadows of the moons on Jupiter as focusing aids.

  November 13, 2002, 11:56 -12:08 UT. A sequence of 8 images compiled from 8, 1 minute AVI clips showing Jupiter's swift rotation beneath the shadow of Io (closest to Jupiter). Europa is on the far side of Jupiter and is moving to the upper right. Note the Field rotation over the 14 minute interval. South is to the upper left. Click on image for a larger view. 

Books

"The New Solar System" edited by J. Kelly Beatty, Carolyn Petersen, and Andrew Chaikin

"Jupiter The Giant Planet" by Reta Beebe

Links

Jupiter

International Outer Planets  Watch (IJW)

Association of Lunar and Planetary Observers (ALPO), Jupiter Section

British Astronomical Association (BAA), Jupiter Section

António Cidadão's Lunar and Planetary Observation and CCD Imaging

Ed Graften's CCD Astro-imaging Page

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