Saturn - The Ringed Wonder 400 Years Later

Since ancient times, observers have noted the movements of Saturn, the most distant planet that can be seen with the naked eye. It’s usually pretty easy to find among the stars, with a yellowish hue and a brightness that sets it apart from the stars around it.

For the amateur stargazer, Saturn has always been a favorite because even in the lowest grade telescopes available today, its magnificent ring system is prominently displayed. Of course, this hasn’t always been the case. The earliest simple telescopes were able to show that Saturn wasn’t just a sphere like the other visible planets, but the nature of the luminous “something” that accompanied it would take many years to identify.

As the art and technology of telescope design advanced, the mysteries of Saturn would slowly reveal themselves:

[Moving your mouse pointer over the picture reveals the names and locations of a sample of Saturn’s ring features shown in the photograph.]

In 1608, the telescope makes its debut in the Netherlands. Hans Lippershey applies for a patent on an instrument variously referred to as a “looker”, or a “spyglass”. But two other gentlemen, Sacharias Jansen and Jacob Metius, come forward and show that they too have constructed their own devices. The patent board isn’t too impressed. After all, the lenses used in the spyglasses aren’t too different in conceptualization from the lenses used in spectacles and those have been sitting on people’s noses for hundreds of years. The upshot is that Hans Lippershey doesn’t get his patent and Jacob Metius receives some small award, but astronomers gain a tool that will transform our understanding of the universe.

Coupled with the soon to be invented microscope, a wholly new era comes to pass. For the first time human beings will be able to witness realities of nature that are invisible without the aid of instruments.

1609: Galileo Galilei of Tuscany improves on the design of the spyglass and explores the Moon. He discovers that its surface is not smooth, but contains mountains and valleys. Galileo calls his instrument a telescope.

1610: Galileo turns his telescope on Jupiter and discovers that it is orbited by what will be called the Galilean moons, Io, Callisto, Europa and Ganymede. To Galileo, Jupiter and its moons resemble a miniature solar system. He explains his studies in a pamphlet entitled Sidereus Nuncius (The Starry Messenger) which confirms the Copernican theory, first put forward by some early Greek astronmers, that the Sun is orbited by the Earth and other planets.

In later life, this view will leave him vulnerable to prosecution by the Inquisition. Under threats of torture and death, he recants and states that he agrees with the Christian assertion that the Sun, Moon, and other planets orbit the Earth. In return, the Inquisition does not burn him at the stake and imprisons Galileo in his home for the rest of his life.

This same year, Galileo turns his telescope to the planet Saturn and although his rudimentary instrument is not powerful enough to resolve its ring system it does show that this planet has a structure different from the other planets. On July 30th, he writes to his Medici sponsors, “…the star of Saturn is not a single star, but is a composite of three, which almost touch each other, never change or move relative to each other, and are arranged in a row along the zodiac, the middle one being three times larger than the lateral ones, and they are situated in this form: oOo.”.

1612: Galileo looks at Saturn and is startled to find no evidence of its strange structure at all! He writes, "I do not know what to say in a case so surprising, so unlooked for and so novel". Galileo does not know that twice in Saturn’s twnty-nine and a half year orbit of the Sun, its ring system is turned edge-on to our view from Earth and it disappears. Among astronomers, this phenomenon is still very popular to “not see”. Galileo expresses confidence that this development concerning Saturn is temporary.

1616: Galileo, still improving the strength of his telescope, and unaware that Saturn’s axial tilt changes its appearance from Earth as Saturn continues its orbit of the Sun, notes for the first time that the planet has a structure that will gradually be recognized as a ring system: “The two companions are no longer two small perfectly round globes ... but are present much larger and no longer round ... that is, two half ellipses with two little dark triangles in the middle of the figure and contiguous to the middle globe of Saturn, which is seen, as always, perfectly round.”

As the years pass and telescopes improve, astronomers around the world work to solve Saturn’s enigma.

1656: In March, Dutch astronomer Christaan Huygens writes of Saturn: “Annulo cingitur, tenui, plano, nusquam cobaerente, ad eclipticam inclinato.” (It is encircled by a ring, thin, plane, nowhere attached, inclined to the ecliptic.)

Saturn’s ring system has been identified. But Huygens understands that scholars will have a hard time with the idea that Saturn could orbit the Sun and its ring will simply go along for the ride “without attaching it by any joints or ties, although imagining that it preserves a uniform distance on every side and revolves in company with Saturn at a very high rate of speed. These men should consider that I do not construct this hypothesis from pure invention and out of my own fancy…”

Huygens describes his idea of some connecting force: “…owing to the great similarity and relationship that exists between Saturn and our Earth, it seems possible to conclude quite conclusively that the former, like the latter, is situated in the middle of its own vortex, and that its centre has a natural tendency to reach toward all that is considered to have weight there, it must also result that the ring in question, pressing with all its parts and with equal force toward the centre, comes by this very fact to a permanent position in such a way that it is equally distant on all sides from that centre.”

In 1666, Isaac Newton will put forward his theory of gravity and things will become clearer.

1675: French astronomer Giovanni Cassini, discovers that Saturn has a gap in its ring. This gap which defines an A and B ring will be known as Cassini’s Division. He also believes that Saturn’s rings are not solid, but are made up of particles.

1837: German astronomer Johann Encke publishes his study of color and brightness variations of Saturn’s rings with particular emphasis on the A ring. A gap in the A ring that was first noted by Henry Kater in 1825 is named for Encke and acknowledges his work.

1850: American astronomers as well as father and son, William and George Bond of Harvard discover Saturn’s C ring, a band of dark semi-transparent material adjacent to the B ring.

1856: Scottish physicist James Clerk Maxwell establishes that Saturn’s rings would have broken apart long ago if they were solid. Instead, they must be made up of fine particles. His work earns him the Adams Prize in 1857.

1969: Pierre Guerin of France observes photographic evidence of possible ring material near Saturn’s C ring. He has discovered the D ring.

Not visible in this Hubble Space Telescope photograph are the broad outermost E and F rings of Saturn.