Observing Project 10D The Majesty of Saturns Rings

The rings of Saturn are the signature image of astronomy, one of the first things that any new amateur is introduced to when he looks through a telescope for the first time. The behavior of the rings over the course of a fifteen-year period is the subject of this project.

In 1995, Saturn passed the autumnal equinox for the northern hemisphere and spring for the south. At that time the planets rings were presented edge-on to Earth and virtually disappeared leaving a naked Saturn. But the only time that all evidence of the rings is completely gone is in the instant that the inclination of the rings is zero. During any given year, the angle at which we view the rings changes slightly because Earth and Saturn do not orbit in exactly the same plane, so even as the rings are about edge on to the Sun, Earth will alternately travel two degrees towards the illuminated plane and then travel about two degrees to the dark side of the rings. When this happens the rings are not quite invisible but can be viewed in silhouette against the planet's disk. The rings may also paint a hairline shadow on the planet's face. By the time Saturn emerged from conjunction the next year, the rings had slowly begun to open as the planet's south pole began to point more towards Earth,we began to get a better and better view of the rings. The rings reappeared in 1996 as a bright slash through the planet and by the year after, they were open wide enough for details to begin to appear.With the rings about 8-10 degrees open, it becomes easier to differentiate the A ring from the B ring and on nights of good seeing, the Cassini division begins to appear.

By 2000, the rings were open by nearly twenty degrees and this began a five-year period where the rings are just at their most magnificent. The rings reached their maximum opening of about 28 degrees in 2003. Now is when we can see the most detail. The A and B rings are clearly visible as distinctly different structures and the Cassini division is obvious even in marginal seeing. On nights of good seeing the inner C ring begins to show itself as a distinctly different structure from the B ring outside of it. At maximum opening, the rings are so wide open that the segment of the rings that is behind the planet tips clear of the planet's disk allowing us to trace the outer circumference of the rings all the way around the planet.

Saturn's rings are bright. The middle B ring reflects more than 60% of the light that falls on them and the A ring about 30-40%. The rings are in fact brighter than the planet itself. Where there is a lot of light available there is the opportunity to use a lot of telescope power so if the air is steady, go ahead and use high power to study the rings.

As of the time this book is published, Saturn's rings are now in the early part of a seven-year long journey towards closure as southern summer progresses. By 2010, the rings will once again reach edge-on and disappear from our sights for a few months. But within a few short months we will begin to see them again as the northern face of the rings, in darkness for fifteen years sees the light of the Sun.

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