A closer look at the rings of Saturn

The rings of Saturn

These evenings, around 10 p.m., depending on how hilly your horizon happens to be, you will see a moderately bright, yellowish, starlike object low in the south-east.

That object is the planet Saturn. It is the sixth planet out from the Sun (we live on the third) and it has been described as the most beautiful object in the Solar System.

If you have binoculars, or better still a small telescope, it is worth a look.

The planets Mercury, Venus, Mars, Jupiter and Saturn have been known almost since the time our ancestors started looking up. They were distinguishable from the stars because, while the stars remained in fixed or extremely-slowly changing patterns, there were starlike objects that moved against the starry background from night to night.

They were called "planetai", Greek for "wanderers". Until the invention of the telescope and the decision by Galileo to use one to look at the sky, nothing more about them was known.

When, in the early 1600s, Galileo pointed his telescope at the sky, he knew about the planets, so he went for them early on. He saw Jupiter as a beige disc and discovered its four largest moons, now named Io, Europa, Ganymede and Callisto.

In his honour, they are also referred to as Galilean satellites. He saw the Moon was covered with mountains, craters and lava flows, which were thought to be seas, and were named accordingly. However, his big shock came when he pointed his telescope at Saturn. It looked oblong to him and sometimes appeared as though it had handles. This planet was different.

A few years ago, at one of our observatory open houses, we had a borrowed replica of Galileo's telescope. It was interesting to see how much telescopes have improved since Galileo's time.

By modern standards Galileo's telescope was a challenge to use. The field of view was tiny, so getting the telescope pointed in the right direction and keeping it pointed must have been a challenge. When looking at bright objects against dark backgrounds, there were fringes of false colour. That Galileo saw as much as he did is a monument to his persistence and patience.

Christiaan Huygens was a dedicated astronomer and telescope maker, and in 1655 he pointed a homemade telescope, which was significantly better than Galileo’s, at Saturn. He reported that Saturn was surrounded by a large ring that nowhere touched the surface of the planet.

He also discovered Titan, Saturn's largest moon. Soon after, in 1675, Giovanni Domenico Cassini, observed that the ring around Saturn was composed of multiple rings, all in the same plane. He also discovered four of Saturn's moons: Iapetus, Rhea, Tethys and Dione.

This is why the recent spacecraft sent to Saturn was called Cassini, and the lander it carried to Titan, Huygens. The rings attracted a lot of interest, and it was soon shown they could not be solid.

Now, thanks to spacecraft, including Cassini, we have had a good, close look at those rings.

They seem to be made up almost completely by small particles of ice, metres in size and smaller, down to millionths of a metre. There are many concentric rings, all less than a kilometre thick. This complicated structure is partially maintained by the pull of nearby moons, with some embedded in the gaps between the rings (shepherd moons).

However, although we know what the rings are made of, and can make computer models as to how they work, we still don't know for sure how or when they formed. Some believe they are long-lived, maybe dating back to the formation of the planet. Others suggest they are no more than a few million years old.

Have a look at them now. We don't know for sure how long they'll last.

Saturn will rise around 9 p.m. and Jupiter around 11 p.m. In hilly places, they will appear later.

Meanwhile, the Moon will be full on Aug. 30.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory near Penticton.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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