Other lords of the rings
No, this is not a sequel to Peter Jackson's epic blockbuster movie The Lord of the Rings.
If you stayed awake in science class the day the solar system was discussed, you know Saturn is circled by a series of concentric rings of material. Called an annular ring, they are composed primarily of countless silica dust and water ice particles (the origin of which is not fully understood), ranging in size from a few micrometres to metres.
Saturn was discovered by Galileo Galilei in 1610. He was the first person to observe the planet using one of the first telescopes ever invented. Viewed from a point well above either the planet's north or south pole, the picture would resemble a multi-ringed dartboard.
The ring system consists of several rings, each of which is labelled with a letter of the alphabet. The three largest, A-C, are considered the major rings, with rings D-G, along with another six smaller and fainter rings, considered minor rings.
The rings vary in composition, width, depth, and apparent colour (actually a factor of their composition rather than any actual colouring). There are several near-empty sections between some of the rings, where particle numbers drop off significantly; the most well known is the Cassini Division (named for the Italian astronomer Giovanni Cassini, who discovered it in 1675), located between the A and B rings.
While the planet's ring system is huge — the largest ring spans about 274,000 kilometres in diameter — the rings are on average relatively thin, only about 200 kms in thickness.
Although Saturn's ring system is constantly losing materials, it is estimated it will last another 300,000 years (so you should still have time to see it). It is hypothesized that Saturn's innermost ring (D), which appears to be the youngest of the rings (at least composition-wise) may have once been a small moon named Veritas (after a Roman goddess said to have hidden in a well) that ventured too close to the planet, and was torn asunder by its tidal forces.
As magnificent as its ring system is, however, Saturn is not the only planet in our solar system with a ring system. Jupiter's ring system, discovered in 1979 via the Voyager 1 spacecraft's flyby, and confirmed by the Galileo spacecraft flyby in 1995, is a faint, four-ring system composed primarily of dust.
The ring system around Uranus (13 rings currently known, with more suspected) was discovered in 1977 and is believed to be composed of debris leftover when small moonlets orbiting the planet collided with one another. The ring system itself is only a few kilometers wide, opaque, and very faint.
Discovered in 1989 by the Voyager 2 flyby, Neptune's six-ring system is, like that of Uranus, faint and tenuous. The rings are very dark, though. It's believed this is due to organic compounds within the rings.
Interestingly enough, other celestial bodies within our solar system's outer regions have been found to have ring systems: Haumea, an egg-shaped minor-planet in the Kuiper Belt two billion kilometres beyond Pluto, has a 70-km wide ring of debris around it; and Chariko (named for the wife of Chiron, and a daughter of Apollo), a small celestial body orbiting between Saturn and Uranus, was discovered to have two rings around it (named Oiapoquue and Chui after two South American rivers). To date, however, there has not been any sign of the one ring to rule them all.
THIS WEEK'S SKY
Mercury is currently too close to the sun to be seen. Venus (magnitude -3.98) is, as it has been for the past several weeks, visible in the pre-dawn sky around 4:50 a.m., reaching an altitude of approximately 20 degrees above the southeast horizon before fading with the break of dawn shortly after 7 a.m.
Mars (magnitude -1.37) is visible in the evening sky as dusk fades, 23 degrees above the eastern horizon, reaching a maximum altitude of 48 degrees above the southern horizon by 9 p.m., and remaining visible until about 2:40 a.m. when it drops below eight degrees above the western horizon.
Jupiter (magnitude -2.07) makes an appearance 20 degrees above the southern horizon around 5 p.m., then heads toward the horizon before setting shortly after 8 p.m.
Saturn (magnitude +0.63) is also visible 20 degrees above the southern horizon by 5:15 p.m., before it, too, drops toward the horizon, and sets around 8:30 p.m.
Until next week, clear skies.
EVENTS
• Nov. 26 — Moon at apogee (farthest from Earth)
• Nov. 28 — Moon at aphelion (farthest from the sun)
• Nov. 30 — Full (Beaver) moon, 6:30 a.m.
Glenn K. Roberts lives in Stratford, P.E.I., and has been an avid amateur astronomer since he was a small child. His column, Atlantic Skies, appears every two weeks.