• The Great Red Spot
  • Cassini at Jupiter: Red Spot Movie
  • Transit Times of Jupiter's Great Red Spot
  • Galileo, Cassini, and the Great Red Spot
  • Een Rode Vlek draait op Jupiter rond (Dutch)

    A.L.P.O. Jupiter Alert

    2002 January 26 / 2002 February 08

    A consensus seems to be forming, within the amateur and professional astronomy communities, that south temperate oval BA should be expected to survive its conjunction with the GRS. Although BA may be affected in several ways, it will probably, according to Dr. Reta Beebe, be slowed somewhat then quickly be propelled past the GRS.

    The visual appearance of BA being split or piled up on another oval was simply other cloud material circulating around BA, and being compressed between BA and the GRS currents.

    Even though BA may not be disrupted, observers must remain alert. Jupiter has surprised us in past apparitions.

    It is important to obtain visual observations documented with disk sketches or strip sketches depicting the GRS and BA interaction, CCD images, or visual central meridian transit timings. These kinds of observations should continue well after BA has passed the GRS.

    The professional community is especially interested in any CCD images obtained in methane.

    CCD images and scanned sketches may be sent to at John W. McAnally. Or mailed USPO to 2124 Wooded Acres, Waco, Texas, USA

    76710. We can also provide A.L.P.O. observing forms.

    John W. McAnally
    The A.L.P.O. Jupiter Section
    Assistant Coordinator
    Transit Timings


    What's Up in Space -- 29 Jan 2002


    Something extraordinary is happening on the planet Jupiter in full view of amateur astronomers: Two gigantic storms are colliding. One is a "white oval" -- a 70-year old hurricane nearly the size of Earth. The other is the famous Great Red Spot -- a centuries-old tempest twice as wide as our planet.

    The pair will likely converge during the weeks ahead, but it will not be a head-on collision because the two storms circle the planet at slightly different latitudes. Nevertheless, the encounter should be dynamic and entertaining. Sky watchers with 6" to 10" telescopes can view the action on clear nights with good atmospheric seeing. Consult a table of Great Red Spot transit times to decide when to look.


    What's Up in Space -- 1 Jan 2002


    The giant planet Jupiter and our own planet Earth will have a close encounter on the first day of the New Year. The two worlds will lie just 4.19 astronomical units apart when Jupiter reaches "opposition" -- that is, a point in the sky directly opposite the Sun -- on January 1, 2002. New Year's Eve revelers in the northern hemisphere can easily find the planet. Simply look straight overhead at midnight: there lies Jupiter -- the brightest "star" in the sky.

  • Finder chart

    For images and Web links for these items, visit http://www.skypub.com


    Telescopic observers from the 19th century may not have had the technological wizardry available to modern-day skywatchers -- but they apparently had an easier time spotting Jupiter's signature feature, its Great Red Spot. According to Amy Simon-Miller (NASA/Goddard Space Fight Center), today this giant cyclonic storm is only about half as big as it was in the 1880s. Simon-Miller and three colleagues confirmed the shrinkage during a careful comparison of historical records and contemporary images from the Voyager, Galileo, and Cassini spacecraft. She presented their results last month at a meeting of planetary scientists.

    Astronomers have known since the early 1900s that the Great Red Spot's longitudinal extent has been decreasing. Late in the 19th century the spot was nearly 35 degrees wide, which corresponds to about 40,000 kilometers, or more than three times Earth's diameter.

    By 1979, when Voyagers 1 and 2 swept past, it had shrunk to 21 degrees (about 25,000 km), yet its latitudinal "height" remained essentially unchanged, about 12,000 km from top to bottom.

    Simon-Miller has discovered that the contraction seems to have picked up steam since the Voyager visits: at its present rate of shrinkage (0.19 degree in longitude per year), the spot will become the "Great Red Circle" by the year 2040. However a perfectly round shape is unlikely, she explains, because the strong, opposing jet streams that confine the spot's northern and southern boundaries will always distort it into an oval.

    No one knows why the not-so-Great Red Spot has shrunk -- or, for that matter, why its color intensifies and fades over time. One clue is that the winds around its circumference are whirling 70 percent faster now (about 700 km per hour) than they were in the Voyager era. Some historical observations suggest that the Red Spot grows and shrinks in a decades-long sequence. "I'm not sure the behavior is really cyclical," Simon-Miller comments, "but I certainly would not be surprised in the least if this shrinking trend slowed or reversed."

    One possible explanation is that deep-seated bursts of thunderstorm-like convection periodically energize the overlying cloud layers, causing the spot to bloat in size, then gradually contract as the turbulence subsides. "All of the weather on Jupiter seems to have sporadic increases in activity," she notes, "so whatever feeds the Great Red Spot likely will too."

    Copyright 2001 Sky Publishing Corporation. S&T's Weekly News Bulletin
    and Sky at a Glance stargazing calendar are provided as a service to
    the astronomical community by the editors of SKY & TELESCOPE magazine.
    Widespread electronic distribution is encouraged as long as these
    paragraphs are included. But the text of the bulletin and calendar may
    not be published in any other form without permission from Sky
    Publishing (contact permissions@skypub.com or phone 617-864-7360).
    Updates of astronomical news, including active links to related
    Internet resources, are available via SKY & TELESCOPE's site on the
    World Wide Web at http://www.skypub.com/.


    31st March 1998


    For well over two years, scientists from the department of Atmospheric, Oceanic & Planetary Physics at Oxford University have been studying weather and cloud formations on a world more than 600 million km away - the planet Jupiter. The latest results of their research will be presented at the UK National Astronomy Meeting on Tuesday 31st March by Professor Fred Taylor, co-investigator for the NIMS instrument on the Galileo spacecraft, which is currently orbiting Jupiter. These results include the revelation of remarkable structure in Jupiter's Great Red Spot.

    The giant planet Jupiter is famous for its colourful, swirling clouds. The most notable feature among this ever-changing turbulence is the Great Red Spot, a huge storm system that could swallow up three Earths and is known to have existed for at least three centuries.

    One of the instruments on board the Galileo orbiter being used to study the Jovian atmosphere and the Great Red Spot is the Near-Infrared Mapping Spectrometer (NIMS). The capability of NIMS to obtain spatial and spectral information simultaneously is ideal for investigating the composition, vertical layering, optical thickness, and fine structure of Jupiter's mysterious cloud layers. The scientists hope that continued observations with NIMS will help to explain a number of the following mysteries:

    1) Although theories abound, it is still not known what gives rise to the bright colorations of the Jovian clouds - for example, the red pigment in the Great Red Spot or the various yellows and browns.

    2) The nature of the circulation which gives rise to the east-west, belt-zone cloud structure is controversial.

    3) What creates and sustains the various giant weather systems (of which the Great Red Spot is just one example of a whole family of different types of giant eddies).

    The analysis of the data is still at a relatively early stage, but several preliminary results will be presented at NAM.


    Jupiter has high winds, and a large number of very large, very long-lived storm systems can be seen on the planet at any one time. The most famous of these is the Great Red Spot (GRS), which is revealed as having a most remarkable structure in the new data. Most astronomers believed it was a deep mass of cloud. Instead, it has a spiral arm structure of clouds, with gaps between which enable NIMS to see through the GRS into the deep, relatively clear atmosphere below. Futhermore, the cloud structure is higher in the centre by more than 10 km and tilted towards one side, something like a crooked spiral staircase. What seems to be happening is that wet air from the deep atmosphere is rising rapidly in a relatively narrow region in the centre of the GRS, and then spraying out above the tops of the ammonia clouds while rotating, rather like a giant garden sprinkler . In some ways this is similar to what happens in a terrestrial hurricane, but the Jovian storm is much bigger than the entire Earth.


    As expected, the main cloud layer on Jupiter is made up of frozen ammonia crystals, and lies at a pressure level of around half a bar (1 bar is the mean pressure at the surface of the Earth). Although anticipated to resemble terrestrial cirrus clouds, the Jovian, ammonia-ice version is made of particles around a hundred times smaller than those in water-ice clouds on Earth.

    The ammonia clouds are overlain by a thick haze at much higher levels in Jupiter's atmosphere. This appears to be a photochemical smog made up of liquid hydrocarbon droplets. A similar layer blankets Saturn's moon Titan and prevents us from seeing Titan's surface. Although thinner than Titan's, the Jovian haze is unexpectedly substantial, and varies with time and place across the planet.

    There is a thicker cloud layer below both the haze and the ammonia cloud. This may be the theoretically-predicted hydrogen sulphide (as NH4SH) cloud at around the one-and-a- half bar level (one and a half times the sea level air pressure on Earth), or a combination of that and an even deeper water cloud. New data is being acquired to try to resolve this point.


    Jupiter's atmosphere is mainly hydrogen, with about 15% helium and a number of minor constituents, the most important of which are measured and mapped by NIMS. Weather on Earth centres around the condensation and evaporation of water. On Jupiter three species, ammonia, phosphine, and water vapour, can condense, making for a remarkably complicated climate. The new data have shown that water, in particular, is very variable. This helps explain the very low water abundance measured by the Galileo probe when it plunged into Jupiters clouds in December 1995. It happened, by chance, to enter a particularly dry region.


    The Oxford researchers are part of an international science team for the Near Infrared Mapping Spectrometer on the Galileo orbiter (Principal Investigator is Dr. Robert W. Carlson of the Jet Propulsion Laboratory in Pasadena, California).

    Galileo is a $1.5 billion NASA mission to explore the Jupiter system at close quarters over a long period. The orbiter has been returning data on the planet and its four largest moons since 7 December, 1995. A probe was also released into Jupiter's atmosphere which returned unique information on the structure and composition of the planets cloud layers. Although the primary mission is now over, the orbiter and the NIMS experiment are in good health and an extended mission is under way. This is focusing on detailed studies of the icy satellite Europa, which is thought to have a sub-surface ocean.


    NIMS images showing full hemisphere views of Jupiter are available on the Web site at:

    Back to ASTRONET's home page
    Terug naar ASTRONET's home page