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1996-01-12
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PHOTO RELEASE NO.: STScI-PRC94-50c RELEASE DATE: November 2, 1994
HUBBLE TRACKS ROTATION OF URANUS
These three NASA Hubble Space Telescope images of the planet Uranus
reveal the motion of a pair of bright clouds in the planet's southern
hemisphere, and a high altitude haze that forms a "cap" above the planet's
south pole.
Hubble's new view was obtained on August 14, 1994, when Uranus was
1.7 billion miles (2.8 billion kilometers) from Earth. These atmospheric
details were only previously seen by the Voyager 2 spacecraft, which flew
by Uranus in 1986. Since then, detailed observations of Uranus's
atmospheric features have not been possible because the planet is at the
resolution limit of ground-based telescopes.
Hubble's Wide Field Planetary Camera 2 observed Uranus through a filter
that is sensitive to light reflected by a pair of high altitude clouds. This
makes a high altitude haze over Uranus' south polar region clearly visible,
along with a pair of high altitude clouds or plume-type features that are
2500 and 1800 miles (4300 and 3100 kilometers) across, respectively.
This sequence of images shows how the clouds (labeled A and B) rotate
with the planet during the three hours that elapsed between the first two
observations (left and center picture) and the five hours that elapsed
between the second pair of observations (center and right picture). Some
cloud motion might be due to high altitude winds on the planet.
(Observations are indicated in Universal Time.)
By tracking the motion of high-altitude clouds, the new Hubble
observations will allow astronomers to make new measurements of Uranus'
rotation period. Based on the previous Voyager observations, Uranus spins
on its axis at a faster rate than Earth does, completing one rotation every 7
hours, 14 minutes.
One of the four gas giant planets of our solar system, Uranus is largely
featureless. Unlike Earth, Uranus' south pole points toward the Sun during
part of the planet's 84-year orbit. Thanks to its high resolution and ability
to make observations over many years, Hubble can follow seasonal
changes in Uranus's atmosphere, which should be unusual given the
planet's large tilt.
Credit: Kenneth Seidelmann, U.S. Naval Observatory,
and NASA
These observations were conducted by a team led by Dr. Ken Seidelmann
of the U.S. Naval Observatory as Principal Investigator. These images
have been processed by Professor Douglas Currie and Mr. Dan Dowling in
the Department of Physics at the University of Maryland. Other team
members are Dr. Ben Zellner at Georgia Southern University, Dr. Dan
Pascu and Mr. Jim Rhode at the U.S. Naval Observatory, and Dr. Ed
Wells, Mr. Charles Kowal (Computer Science Corporation) and Dr. Alex
Storrs of the Space Telescope Science Institute.