Mar 29, 1999
Huge springtime storms hit the planet Uranus
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A dramatic new time-lapse movie by NASA's Hubble Space Telescope shows for the first time seasonal changes on the planet. Once considered one of the blander-looking planets, Uranus is now revealed as a dynamic world with the brightest clouds in the outer Solar System and a fragile ring system that wobbles like an unbalanced wagon wheel. The clouds are probably made of crystals of methane, which condense as warm bubbles of gas well up from deep in the atmosphere of Uranus.
Right: Last august the Hubble Space Telescope captured this near infrared image of Uranus. Recent analysis indicates that clouds seen here in orange appear to circle Uranus at speeds in excess of 500 kilometers per hour. Comparisons to earlier photographs show a slight precession shift in the brightest of Uranus' rings.
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Although Uranus has been observed for more than 200 years, "no one has ever seen this view in the modern era of astronomy because of the long year of Uranus -- more than 84 Earth years," said Dr. Heidi Hammel, Massachusetts Institute of Technology.
The seasonal changes on Earth are caused by our planet's rotational pole being slightly tilted. Consequently, the Earth's Southern and Northern hemispheres are alternately tipped toward or away from the Sun as the Earth moves around its orbit. Uranus is tilted completely over on its side, giving rise to extreme 20- year-long seasons and unusual weather. For nearly a quarter of the Uranian year, the sun shines directly over each pole, leaving the other half of the planet plunged into a long, dark, frigid winter.
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Uranus was discovered March 13, 1781, by William Herschel. Early visual observers reported Jupiter-like cloud belts on the planet, but when NASA's Voyager 2 flew by in 1986, Uranus appeared as featureless as a cue ball. In the past 13 years, the planet has moved far enough along its orbit for the sun to shine at mid- latitudes in the Northern Hemisphere. By the year 2007, the sun will be shining directly over Uranus' equator.
Karkoschka, Hammel and other investigators used Hubble from 1994 through 1998 to take images of Uranus in both visible and near-infrared light.
The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. Web Links
NASA/STScI Press release - Mar. 29, 1999
Infrared Uranus - Astronomy Picture of the Day, Oct 20, 1998
Uranian Moons, Rings, And Clouds - Astronomy Picture of the Day, Nov 26, 1997To learn more about Uranus, visit Bill Arnett's Nine Planets web site.
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