Saturn at Equinox: APOD: 2014 September 21 - Saturn at Equinox
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.
2014 September 21
Explanation: How would Saturn look if its ring plane pointed right at the Sun? Before August 2009, nobody knew. Every 15 years, as seen from Earth,
Saturn's rings point toward the Earth and
appear to disappear. The
disappearing rings are no longer a mystery -- Saturn's rings are known to be
so thin and the
Earth is so near the Sun that when the rings point toward the Sun, they also point
nearly edge-on at the Earth. Fortunately, in this
third millennium, humanity is advanced enough to have a spacecraft that can see the rings
during equinox from the side. In August 2009, that Saturn-orbiting spacecraft,
Cassini, was able to snap a series of unprecedented pictures of
Saturn's rings during equinox. A digital composite of 75 such images is
shown above. The rings appear
unusually dark, and a very thin ring shadow line can be made out on Saturn's cloud-tops. Objects sticking out of the ring plane are
brightly illuminated and cast
long shadows. Inspection of these images is helping humanity to understand the specific
sizes of Saturn's ring particles and the
general dynamics of
orbital motion. This week, Earth undergoes an
equinox.
