As Saturn's rings orbit the planet, a section is typically in
the planet's shadow, experiencing a brief night lasting from 6
to 14 hours. However, once approximately every 15 years, night
falls over the entire visible ring system for about four days.
This happens during Saturn's equinox, when the sun is directly
over Saturn's equator. At this time, the rings, which also orbit
directly over the planet's equator, appear edge-on to the sun.
During equinox, light from the sun hits the ring particles at
very low angles, accenting their topography and giving us a
three-dimensional view of the rings. "The equinox is a very
special geometry, where the sun is turned off as far as the
rings themselves are concerned, and all energy comes from
Saturn," said Dr. Michael Flasar of NASA's Goddard Space Flight
Center in Greenbelt, Md. During Saturn's latest equinox August
11, the rings reached a temperature of 382 degrees below zero
Fahrenheit, the coldest yet observed, as seen by the Composite
Infrared Spectrometer (CIRS) i