Saturn's Disappearing Rings

The title of this column may sound alarming to some. And if you took a quick telescopic look at Saturn on the next clear night it would appear that the sixth planet from the Sun seems to be losing its ring system. While astronomers believe Saturn’s rings will eventually all “rain” down onto his cloud tops in 50 to 100 million years and cease to exist, the current scenario is not so dire.

In the course of Saturn’s almost 29½ year orbit of the Sun, our Earthly perspective affords us a view of this magnificently ringed world from different angles. Sometimes Saturn’s north pole is tilted away from us, allowing us to view the southern or bottom “surface” of the rings (this is the current situation). At other times the north pole is tilted towards us, and we see the northern or top surface of the rings.

However, in between these views is a time when our perspective allows us to see the rings edge-on, an event called a ring-plane crossing. Imagine a piece of paper slicing through Saturn at his equator, and that you are looking directly at that thin edge of the paper. Ring plane crossings occur about every 15 years. Please visit the following website to view a diagram showing the reason for the changing aspect of Saturn’s rings as seen from the Earth: http://astrocoffeehut.files.wordpress.com/2008/03/changing-aspect-saturn-rings_sm.jpg

I’ve seen this edge-on view on a couple of occasions during my 35+ years of observational astronomy. I knew another ring plane crossing was going to occur this year, but until last fall I did not realize we would not be able to see the upcoming one on September 4. Why? Saturn will be too close to the Sun in our sky to be seen from the Earth. And what’s even worse, the next one in 2025 will not be a favorable event either.

However, if you’ve not seen Saturn for quite some time, you will be somewhat surprised when you observe it now. During the beginning of March the rings were tilted only 2.3 degrees from the horizontal, and we were still looking at the southern surface of the ring system. Through the beginning of May the rings will open up just a little wider (the tilt increases so we see more of the rings). Then the tilt begins to shrink until we lose Saturn in the Sun’s glare.

If you wish to observe Saturn with your own telescope you can still find him in the constellation of Leo. Regulus is the bluish-white star at the bottom of the “sickle-shaped” pattern that marks the head and front quarters of the lion. (This asterism also looks like a backwards question mark, with Regulus in the location of the period.) Saturn will be down and to the left. On April 1 at 7:30 pm Saturn will be about 40 degrees above your southeast horizon.

Or visit Seagrave Observatory in North Scituate or Ladd Observatory in Providence to observe beautiful Saturn through the larger telescopes at each facility. Check out the websites for the public night schedules. Even with a small telescope with lesser quality optics you’ll still see the rings despite their almost edge-on appearance. Your view will even be better than what Galileo saw when he first observed Saturn in July 1610 at a magnification of 30 times with his one-inch in diameter lens telescope. He was unable to resolve or distinguish the rings. He observed what he believed to be two moons on either side of Saturn’s disk (it looked like Saturn had ears or handles), which didn’t change position like Jupiter’s moons did. Galileo soon lost interest.

When he next visited Saturn the moons were gone! This event was something Galileo could not explain, and he died before the true nature of his observation was discovered. It just so happens that when Galileo revisited Saturn the Earth was crossing the ring-plane, and the rings (Galileo’s two moons) disappeared.

It is amazing Saturn’s rings are visible at all, considering the planet’s distance from the Earth (at the beginning of April – 788,000,000 miles), and the fact that the ring plane is only about 328 feet thick (just larger than the length of a football field). Detail usually seen in the rings all but disappears at this time. By the time of the ring-plane crossing on September 4, Saturn will have moved away from us and will be over 968,000,000 miles from the Earth.

The rings are comprised of irregularly shaped dirty snowballs, ranging in size from grains of dust to many particles the size of pebbles. There are also some “boulders” as large as a car or small house sized bodies. They all orbit Saturn along the planet’s equatorial plane.

It is indeed unfortunate we do not witness the ring plane crossing, but the narrow aspect of the rings does allow us to concentrate on the disk of Saturn himself and to follow some of his retinue of Moons more easily. Though you can focus your attention on the planet’s salmon-colored cloud tops, the bands in Saturn’s upper atmosphere are much less prominent than those of Jupiter. (Very little cloud detail can be seen in small telescopes.) And a few of Saturn’s brighter moons will be more apparent as they parade around the planet. The brightest will be Titan, which orbits Saturn in 16 days.

Take this opportunity to view Saturn from a fairly unique perspective. After September 4, Saturn’s north pole will begin to tilt towards us, the rings will begin to open up, and we will then see the northern or top surface of the rings until the next ring-plane crossing in 2025.

As always, keep your eyes to the skies.