Sky Talk April 2010: Saturn’s Rings Reappear

Last year, the sky’s most spectacular planet and one of astronomy’s greatest icons — magnificent Saturn — “lost” its rings as seen in most telescopes. (See the March installment of Sky Talk.) And what bad timing, for 2009 was the International Year of Astronomy when millions of people around the world got their first look through a telescope only to see a ringless Saturn! But now the rings are returning to again thrill stargazers.

Twice during Saturn’s 30-year orbit of the Sun, its ultra-thin ring system (only 100 feet thick in most places!) passes through the plane of our view from the Earth, causing the planet to appear without rings. For much of last year the rings were tilted less than 3 degrees to our line of sight, making their visibility in small scopes difficult. At the time they actually went edge-on (when only the Hubble Space Telescope and the very largest of optical telescopes could have detected them) Saturn was in conjunction with the Sun and no longer visible. But now it’s well placed for viewing again in the southeastern sky on April evenings and rising higher each night.

Normally, the 35x eyepiece on the Scientifics 60mm refractor or the 30x one on the Astroscan 105mm wide-field reflector will show the rings when fully open. But right now, it will take a magnification of least 60x and a very steady night to reveal them. (In the case of the little 75mm commemorative FirstScope Dobsonian reflector (#31512-75) added to the Scientifics line last year, its 75x eyepiece will be needed.) What will be seen is not so much an actual ring around the planet but rather a luminous line extending from either side of its equator.

Saturn will remain visible in the evening sky into September, and as the year progresses its ring system will slowly open to our view. By the time the planet disappears into the evening twilight at Summer’s end, the rings will be inclined about 5 degrees to us (eventually reaching a maximum tilt of 32 degrees some seven years from now), and by then appear as a true ring rather than a line. It’s great fun watching this transition occur and seeing Saturn finally becoming the ringed world again that makes it so famous. Those readers fortunate enough to own one of the many fine larger instruments in the Scientifics line of telescopes will truly have a “ring-side” seat at this celestial unveiling!

When Galileo first viewed Saturn in 1610 with his optically primitive telescope he described it as looking like a triple planet or a cup with “handles.” But several years later when he saw it again, the handles has vanished! When he first viewed it, the rings were nearly wide open — but in the interim they had turned edgewise and completely disappeared, leaving him (understandably) quite perplexed. Had he continued his observations of the ringed planet longer, he would have had the honor (and thrill!) of discovering what was actually happening. As it was, that fell to the noted Dutch astronomer Huygens in 1665 using a much superior telescope to those of the Italian astronomer.

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


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