Disappearing rings? What's this guy talking about? People have been entranced by Saturn's glorious ring system since Galileo first spotted them in 1610.

His telescope wasn't very strong, so the rings looked like ears, or jug handles to him. But the advent of better telescopes brought the complex, and ultra-thin ring planes into clearer view. And no one who sees them through a good telescope ever forgets his/her first view.

Saturn and its halo are an image you've seen since childhood - an icon representing all of outer space. Here's an amazing Hubble movie of Saturn rotating inside of its rings.

But the magic of celestial mechanics periodically makes the rings vanish, as the Earth passes through the ring system's plane twice during each of Saturn's 29-year orbits around the sun. That brings them into an edge-on perspective with respect to Earth. Like a dinner plate, the rings may present a broad expanse to our eyes when the angle is steep. But tilt it back to edge-on, and the dinner plate becomes a thin line.

In Saturn's case the rings are so thin they virtually disappear. Two years after Galileo discovered them, the rings "vanished." He was baffled.

And that's where we're headed now. Saturn is visible on any clear evening this spring, high overhead in the constellation Leo. By April 30, our view of Saturn's rings will show them at an angle of just under 10 degrees from edge-on. And that will be our last, best view of the ring system for the next several years.

The last time this happened was in 1995 and 1996, when the ring angle shrank to zero. Then it began to increase again, reaching a maximum of 27 degrees in 2003, a climax that occurs about every 14 years. It's been diminishing ever since, and slips to zero degrees again in September 2009.

Here's how the 1995-96 event looked to Hubble.