Don't look now but Saturn is losing its rings. Actually, do look as the famed ringed planet is still a beauty, and its rings really aren't going anywhere-- it just looks that way.

In 1610, the year Galileo discovered Jupiter's four largest moons with his new telescope, he also viewed Saturn and saw that something was different. But with his crude telescope--inferior even to today's department store scopes--he misinterpreted what he saw as he wrote, "the planet Saturn is not one alone, but is composed of three, which almost touch one another...the middle one is about three times the size of the lateral ones."

Two years later, he was perplexed when Saturn's companions disappeared: "Have they vanished or suddenly fled? Has Saturn, perhaps, devoured his own children? Or were the appearances indeed illusion or fraud?" Later, when the secondary bodies reappeared, he was even more dumbfounded. Sadly, he died never knowing what he had discovered and having no clue about the mysterious disappearance and reappearance of his discovery.

The quality of telescopes rapidly improved, and the mystery was solved in the decade following Galileo's death. Christiaan Huygens determined that surrounding Saturn is a "flat ring which nowhere touches the body of the planet." He referred to the rings in the singular as he thought they were one solid body; we now know there are dozens of flat rings, each composed of millions of small icy particles.

In 1659, Huygens explained the rings' periodic disappearance. Like Earth, Saturn is tilted on its axis, so at different points in its orbit around the Sun, we see its rings at different angles. About every 14 3/4 years (twice during each Saturnyear of 29 1/2 Earth-years) we see the rings edge-on. Being only a mile or so thick, from our distance of 800 million miles, they seem to vanish for a few weeks.

Huygens' diagram helps visualize this. The inner views of Saturn show the planet as it orbits the Sun; the outer views show how the planet and rings appear to us at each corresponding point.

Saturn's rings, now slightly tilted, are still visible, but the tilt gradually decreases over the next few months until early September when we cross the ring plane. At that point, the rings will seem to disappear once more--showing us the sight that so mystified Galileo nearly 400 years ago. Unfortunately, by September Saturn will be close to the setting Sun and difficult to see in the twilight. So find a telescope and take look now as this won't happen again until 2024.

Sky Calendar

* Apr. 22 Wed. morning: The Lyrid meteor shower peaks about 5 a.m. and Venus is just below the crescent Moon at dawn.

*24 Fri.: The Moon is new.

*26 Sun. evening: Mercury is below the crescent Moon at dusk low in the west.

*May 1 Fri.: May Day and Beltane, a cross-quarter day celebrating the middle of spring, and the Moon is at 1st quarter.

*May 3 Sun. evening: Saturn is to the upper left of the gibbous Moon.

* 6 Wed. morning: The Eta Aquarid meteor shower peaks with the Moon setting 2 hours before sunrise.

* 8 Fri.: The full Moon is called Milk Moon and Planting Moon.

Naked-eye Planets. Evening: Saturn is high in the southeast with Mercury low in the west northwest at dusk. Morning: Jupiter is the brightest object in the east southeast as "morning star" Venus and much fainter Mars (to Venus' lower right) are just above the eastern horizon before dawn.

Paul Derrick is an amateur astronomer who lives in Waco. Contact him at 918 N. 30th, Waco, TX 76707, (254) 753-6920 or paulderrickwaco@ aol.com. See the Stargazer Web site at stargazerpaul. com.