Hubble images reveal dynamic seasons on Uranus
March 30, 1999
(CNN) -- A dramatic new time-lapse movie by NASA's Hubble Space Telescope shows for the first time seasonal changes on the planet.
The series of images reveal Uranus 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, according to NASA.
The movie, created by Hubble researcher Erich Karkoschka of the University of Arizona, clearly shows for the first time the wobble in the ring system, which is made of billions of tiny pebbles. The wobble may be caused by Uranus' shape, which is like a slightly flattened globe, along with the gravitational tug from its many moons.
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 the 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.
Uranus, a gas giant some four times larger than Earth, 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.
Hubble surveys 6 spiral galaxies
Space Telescope Science Institute
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