PHOTO RELEASE NO.: STScI-PR91-04              FOR RELEASE: January 17, 1991

PHOTO CAPTION

NASA's Hubble Space Telescope Views Major Storm on Saturn

The accompanying movie shows the Saturn white spot, a great storm in the 
equatorial region of Saturn, discovered by amateur astronomers in September, 
1990.  Such storms are rare: the last one in the equatorial region occurred in
1933.  The movie contains one complete rotation of Saturn.  The storm extends
completely around the planet, in some places it appears as great masses of 
clouds and in others as well-organized turbulence.

Knowing that this storm is probably a once-in-a-lifetime event, scientists and
engineers of a special White Spot Observing Team, the Wide Field/Planetary
Camera Team, the Space Telescope Science Institute, and the Goddard Space 
Flight Center reprogrammed the observing schedule of the Hubble Space Telescope.
They were able to get several days of Saturn observations in mid-November 1990, 
shortly before Saturn moved too near in the sky to the Sun for safe 
observations by HST.

The movie was constructed from red, green, and blue Planetary Camera images 
obtained during eight successive HST orbits on November 17, 1990.  Each of the 
24 frames was processed to remove instrumental artifacts and the effects of the 
HST spherical aberration.  The frames were then combined to make the movie by 
interpolating images of Saturn at uniform intervals of about ten minutes, or 
six degrees of rotation of Saturn.  The color in the movie is approximately 
"true color."  The occasional dark swaths running North-South are an artifact 
of joining the individual frames.  The processed frames reveal detail down to 
about 700 km (440 miles), but there is some loss in resolution in constructing 
the movie.  For comparison, the diameter of Saturn is about 120,000 km (75,000 
miles).

The images used in the movie are only about fifteen percent of the data 
acquired during the November 1990 observing session.  By studying all the data, 
scientists hope to better understand wind speeds in Saturn's atmosphere, the
composition and altitude of the clouds, and perhaps help to understand the
cause of this great storm.

Credit:   NASA