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Moon, Saturn, and Spica

November 21, 2011

[SFX: Saturn audio]

The eerie sounds of the planet Saturn are telling a tale of two hemispheres.

As Saturn rotates, its magnetic field produces radio waves, which are recorded by the Cassini spacecraft. Cassini scientists convert the data to sound.

The radio waves are one way that scientists measure the length of Saturn’s day. Saturn is a big ball of gas with no solid surface, so there are no fixed landmarks to track as it spins. But the radio waves repeat as the planet rotates, providing a way to measure how fast Saturn is spinning: once every 10 hours and 40 minutes.

Over the last few years, though, scientists realized that the radio waves coming from the northern and southern hemispheres were out of sync. And as the seasons on Saturn changed, so did the radio waves. As the Sun moved from southern to northern skies, the cycle of radio waves got shorter in the south and longer in the north — as though the two hemispheres were rotating at different speeds.

That’s not actually the case, though. Instead, the changing levels of solar energy are most likely causing the two hemispheres of Saturn’s magnetic field to “sing” a bit out of tune.

Look for Saturn near the crescent Moon in the southeast at first light tomorrow. The star Spica is close to the left of the Moon, with fainter Saturn a little farther to the left of Spica.


Script by Damond Benningfield, Copyright 2011


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