Take time to check out Saturn’s rings


By Tom Burns - Stargazing



The most spectacular sight in a telescope is Saturn and its fabulous rings. The planet is starting to dive toward the western horizon in the early evening, but there are still a few weeks to check it out before Earth blocks the view.

If you don’t have a telescope, now is the time to schedule a visit to a local observatory near you.

Binoculars won’t help you here. Saturn is gigantic, but it is also really far away as planets go. However, even a small telescope will show its fabulous ring system.

Look to the SSW after it’s good and dark. Saturn is the bright yellow “star” in the constellation Capricornus, the oddly named “Sea Goat.”

At 75,000 miles in diameter, Saturn is the second largest planet after Jupiter, and at 887 million miles away right now, it’s the farthest from the sun of all the planets visible to the unaided eye.

It takes more than 29 years for Saturn to orbit the sun. It makes no more than three such trips during the average human life. For that reason, Saturn moves very slowly against the background stars of the zodiac.

Saturn averages about 240 degrees below zero on its surface, but, like all the “gas giant” planets, it cannot be said to have a surface. Like most outer planets, Saturn is, on the surface at least, a great gasbag.

Like Jupiter, underneath its dense atmosphere, it is composed chiefly of liquid hydrogen, with a smattering of helium, ammonia, and methane ice crystals thrown in.

Saturn is thus not a very heavy planet. Its specific gravity is less than water, a scientific way of saying that if you could arrange a pan of water big enough, Saturn would float!

Saturn’s gassy surface doesn’t show much detail, but look for the rings’ shadow as a curved dark band projected on the planet.

And look for a dim point of light some distance outside the rings. You’re seeing Titan, the biggest and brightest of Saturn’s 63 confirmed moons. At 3,500 miles in diameter, Titan is wider than the planet Mercury.

Okay, okay, now look at the rings. This year, they are tilted in such a way as to expose their structure well. They look like a rakishly tilted hat brim.

Over the next few years, the rings will change their tilt and become less visible. By 2025, they will look like a line cutting the planet in half. For about four days, they will not be visible at all.

(A digression: In my infinite wisdom as director of Perkins Observatory, I managed to schedule a Cub Scout program at the observatory during those four days in 2009. The Perkins staff and volunteers will forever remember the date as the Great Cub Scout Riot.)

The rings you can see in a ‘scope are about 170,000 miles in diameter, more than twice as wide as the planet’s disk.

But close-up views from the Voyager and Cassini space probes reveal fainter outer and inner ring segments invisible from Earth.

The outer rings extend out to a diameter of at least 600,000 miles. The inner rings float a mere 5,300 miles from Saturn’s cold cloud tops.

Despite their enormous width, the rings are extraordinarily thin, no more than a mile thick in most places. That’s thinner than a piece of paper if you scaled it up to Saturnian size.

Although the rings look solid in a telescope, they are primarily composed of jagged pieces of water ice and a smattering of rocky meteoroids that probably average no more than a few feet in diameter.

The pieces aren’t very closely packed together, either. When Saturn passes in front of a star, the star is usually visible through the rings.

I have written previously about scientific speculations concerning the origins of Saturn’s rings. The bottom line: Despite visits by spacecraft, astronomers still aren’t sure whether the rings formed recently or long ago. The most prevalent speculation is that the brighter rings formed when one of Saturn’s smaller moons shattered from Saturn’s enormous gravity. Stay tuned.

My earliest astronomical memory is the view of Saturn’s rings through a neighbor’s telescope. That single view sparked a lifelong interest in astronomy.

A whole generation of children is waiting to be delighted in the same way. If you have a telescope, take them out and give them a look.

While you’re at it, tell the kids the story of Old Father Time.

They should recognize him. We see him mostly, sickle in hand, on New Year’s Eve, passing on the burden of the coming year to the New Year’s baby.

Father Time is older than you might think. He has moved slowly and inexorably across the sky for eons. As the autumn progresses, you may see him, much as our ancient forebears did, marking the passing of the days, months, and years.

He is Saturn, the deity responsible for time and agriculture. He is visible just after dark as a bright, orange-yellow point of light low in the southwestern sky.

Because Saturn was the slowest moving of the planets visible to them, the ancients saw it as a symbol of the slow passage of the years. The Greeks called it/him Cronus, Father Time, the father of all the gods on Mount Olympus. He was also in charge of fertility. He made the plants and animals grow and multiply, passing their seed on through time into the next generation. That’s why, to this day, Father Time still carries his scythe, ready to harvest the Earth’s bounty.

Cronus was not, strictly speaking, a god but a Titan, the beings who ruled the universe before the gods came to power. He came to power by driving out his father, Uranus, the god of the sky, with his sickle. Having heard a prophecy that he, in his turn, would be deposed by one of his children, he swallowed them whole as they were born. The only child to escape Cronus’ weird culinary habits was Zeus, called Jupiter by the Romans. His mother, Rhea, smuggled him to the island of Crete, where he grew to manhood.

Cronus was tricked into vomiting up his other children, and they joined forces with Zeus to overthrow their father. After a 10-year war, Zeus and the other gods were triumphant, and they threw Cronus into Tartarus, the deepest bowels of the Earth, below even Hades. For all his faults, Cronus was a kind and gentle deity. His rule brought a golden age to Earth — a period when time and nature were bountiful. The crops grew without fail, and time moved with the slow softness of a summer breeze. Humans lived like the gods themselves, and even death was no worse than a gentle dream. With his banishment, the age of death and change began.

The age of the gods came and human fate moves now with their fickle whims. (Try living in your father’s stomach for a while and see what it does for your disposition.) Crops sometimes are bountiful, and sometimes they fail. The seasons are inconstant, and death is the inevitable end of life. The old gods and titans are gone now. We see their ghosts as those bright points of light, the planets that wander slowly among the stars. Perhaps you will think of Cronus as you look at his rings through a telescope this autumn. He wears them low on his head like a triumphant wreath of golden ivy. Of course, the ancients didn’t know about the rings, but it is well that Cronus should be so crowned. In a sense, Father Time still rules.

We are still bound by the brief years we dwell upon our planet, by the inexorable flow of time during our all-too-brief residence here. Time, Cronus’ gift to the world, is still our greatest joy — and our greatest sorrow.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.