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Equinox at Saturn
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Since 2004, Cassini’s Composite Infrared Spectrometer (CIRS), has collected data on the thermal behavior of the main rings of Saturn. 
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Saturn experiences Equinox as Earth does every spring and fall.
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But seasons on Saturn are much longer.
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It takes around 30 years for this gas giant to complete a full orbit around the sun...
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so an Equinox occurs roughly every 15 Earth years.
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Because Saturn’s rotational axis is tiled with respect to its orbital plane,
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from the sun, Saturn appears to show its rings at different angles at different points in its orbit.
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For nearly half of Saturn’s orbit, the sun shines on the south side of the rings.
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For the other half, it shines on the north side.
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And every time the rings cross Saturn’s orbital plane, Equinox happens.
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As less and less solar energy heats the rings, they cool down.
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From 1994 to 2009 the sun illuminated the south side of the rings.
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Cassini’s Composite Infrared Spectrometer had a unique view of the cooling of the rings.
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Animation shows sun angle changing from December 2004 to August 2009 and shows temperature changes in the rings.
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Equinox
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The temperature of the side of the rings hidden from the sun changes, too.
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Animation shows sun angle changing from December 2004 to August 2009 and shows temperature changes in the rings.
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Equinox
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NASA, Jet Propulsion Laboratory, California Institute of Technology
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