Saturn's Vanishing Rings

Saturn's famous rings will disappear today

Named after the Roman god of agriculture, the sixth planet from the sun is best known for its rings, which likely formed 4.5 billion years ago, at about the same time the Earth was born.

And since then, every fifteen years, Saturn's rings "disappear," in what astronomers call the "ring plane crossing" illusion.

"The magician's tools required to perform this trick are pure sunlight, a planet that wobbles, and a main ring system that may be almost 200-thousand miles wide, but only 30 feet thick," says Linda Spilker, deputy project scientist for the Cassini Saturn mission at NASA's Jet Propulsion Laboratory in Pasadena, California, in a recent press release.

"Whenever equinox occurs on Saturn, sunlight will hit Saturn's thin rings, the ring plane, edge-on," said Spilker." The light reflecting off this extremely narrow band is so small that for all intents and purposes the rings simply vanish."

"The best Saturn viewing window is ending, but the dramatic narrowing of the rings is worth attempting through a telescope," according to Cassini's Saturn Observation Campaign, which invites professional and amateur astronomers to participate.

"Look for Saturn very low on the Western horizon just after sunset. It sets an hour after sunset by month’s end. The rings have narrowed to only 1.9 degrees this month. The Sun passes through Saturn's ring-plane on August 10th. The south face of the rings are very slightly tilted towards Earth, and the previously bright sun-lit ring, which looks like a straight line, will appear to have gone dark as we get a glimpse at the dark north side of the rings for the first time. Look for Saturn near Mercury on the 18th and near the moon on the 25th."

Humans started witnessing this phenomenon since 1612, when Galileo observed it and wrote, "I do not know what to say in a case so surprising, so unlooked for and so novel."

Medieval thinkers associated Saturn with melancholy, one of the four humors of ancient medicine. But if you manage to get a view of our solar system's second-largest planet and don't see its rings, don't be sad -- they're still there.

GET INVOLVED

• Participate in Cassini's Saturn Observation Campaign (The Cassini Equinox mission invites professional and amateur astronomers plus interested members of the public to join the Saturn Observation Campaign)
• Sign a petition to add the option for US taxpayers to contribute to NASA on the IRS 1040 tax form
  
• Donate to the American Astronomical Society
  
• Download this month's free night sky map and calendar from Skymaps.com

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image: The Cassini spacecraft looks toward the sunlit face of Saturn's rings, whose shadows continue to slide southward on the planet toward their temporary disappearance during equinox in August 2009. This two-frame color mosaic was created from images taken as part of a photometry observation of the rings. Photometry observations are useful for determining a host of ring particle properties. This view looks toward the sunlit side of the rings from about 3 degrees below the ringplane. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were acquired with the Cassini spacecraft wide-angle camera on Aug. 22, 2008 at a distance of approximately 1.2 million kilometers (728,000 miles) from Saturn. Image scale is 66 kilometers (41 miles) per pixel. (image credit: NASA/JPL/Space Science Institute)