Sky Talk March 2009: Saturn Without Rings!

The magnificent ringed-planet Saturn is now well placed for viewing in the southeastern sky on March evenings. Unfortunately, for many who will be looking at it for the first time during this very active International Year of Astronomy, it will be a disappointment in small telescopes-for it will be seen nearly ringless!

Twice during each of Saturn’s 30-year orbits of the Sun, its ultra-thin ring system passes through the plane of our view from the Earth, causing the planet to appear without rings. Indeed, over the past couple of years the rings have been closing up, resulting in Saturn appearing much fainter than it does when they are wide open and reflecting added sunlight to that of the planet’s globe itself.

During March, the rings will be tilted just 3 degrees to our line of sight. Their visibility in small scopes like the Scientifics’ 60-mm refractor (#30823-61) will depend on having a steady atmospheric to look through (or good “seeing” as stargazers call it) and the training of the observer’s eye. Its 87X eyepiece should show them as a razor-thin line extending outward on either side of the planet’s equator. The 4-inch and larger telescopes in the Scientifics catalog will definitely show the rings at magnifications of 100X or more throughout the Spring. However, by the time the rings actually go fully edge-on to the Earth in early September, not even the largest telescope in the catalog will show any trace of them! (This actually occurs this time while Saturn is on the opposite side of the Sun from us and would not be visible in any case.)

Another fascinating phenomenon accompanies the ring passage. Saturn’s satellites, several of which are visible even in a 60-mm glass, lie in the same plane as the rings and as they orbit the planet they appear like beads on a string (the rings) slowly moving to and fro from one side of its globe to the other. It’s also fun to see when the rings finally disappear completely in small telescopes and then when they first reappear. When Saturn becomes visible again in the morning sky in October, the rings will have begun slowly opening to view. By the end of this year, they will be tilted about 5 degrees to us and will eventually reach a maximum tilt of 32 degrees some eight years from now. The next ring-plane crossing will happen in the year 2025.

Interestingly, when Galileo first looked at Saturn in his optically primitive telescope, he described it as a cup (or planet) with “handles.” But several years later when he viewed it again, the handles has vanished! When he first saw it, the rings were nearly wide open — but in the interim they had turned edgewise and completely disappeared, leaving him (understandably) very perplexed.

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of five books on stargazing.


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