Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

April 28, 1997
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Io's Sodium Cloud
Galileo Project, JPL, NASA

Explanation: Io has its own cloud. Jupiter's most active moon is visible on the left of the above false-color photograph, with its left side illuminated by sunlight. But what is happening on Io's right side? Here a plume of gas from the active volcano Prometheus also reflects sunlight. A second active volcano, Pele, is also visible: marked by the red spot just below Io's center. Surrounding the moon is a yellow haze originating from gas ejected by Io's volcanos. Sodium atoms in the gas cloud are particulary efficient at reflecting yellow light. Several points of light are background stars.

Tomorrow's picture: Hale-Bopp and Orion

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U.