In addition, to more clearly view the rings the astronomers timed their observations to match a rare alignment that occurs only once in forty-two years (on May 3, August 16, 2007, and, later, February 12, 2008): the rings appear edge-on to the Earth, what is called a ring-plane crossing. They will also take images on December 7, 2007, when the rings appear edge-on to the Sun.

Uranus takes approximately 84 years to travel around the Sun, which is why this event only occurs once every 42 years, twice during one complete circuit about the Sun.

This alignment called the ring-plane crossing actually makes it appear that the ring is cutting the planet in two. An excellent photograph showing this effect (which was produced by Keck 2) appears at the CBC Science and Technology news website “Uranus 'dark side' image reveals changing rings”.

Lead astronomer Imke de Pater, at the University of California, Berkeley, United States, and fellow collaborators directly used the ground based telescopes of the Keck 2 (W.M. Keck Observatory, one of the world’s largest optical/infrared telescopes, located in Hawaii, United States); the Very Large Telescope (European Southern Observatory, a system of four separate optical telescopes, located in Chile); and a telescope at the Palomar Observatory (California, United States).

Much of the improvement in clarity with the images was due to a high-tech adaptive optics system recently installed on the Keck 2 telescope. Adaptive optics is a technology used to improve the performance of optical systems, such as telescopes, by minimizing the negative effects of such distortions as that found within Earth’s atmosphere.

The astronomer team also used the space based Hubble Space Telescope (National Aeronautics and Space Administration). The Advanced Camera for Surveys (ACS), onboard of Hubble, also helped to produce the clearer pictures of Uranus’ rings. The ACS was affixed to Hubble during the NASA space shuttle repair mission (STS-109) in March 2002.

The advantage of viewing the rings when they are edge-on to the Earth is because the outer rings are less bright than normal, while the inner rings actually become brighter.

De Pater said of their findings, “People tend to think of the rings as unchanging, but our observations show that not to be the case.” He went to say, "There are a lot of forces acting on small dust grains, so it is not that crazy to find that the arrangement of rings has changed."

In fact, when the spacecraft Voyager 2 photographed the rings of Uranus in 1986 the dust that surrounded the rings appeared to be embedded within the rings. However, the photographs taken by de Pater’s team showed the dust to be enveloping the rings like a cloud. In the twenty plus years between the images, the rings appear to have relocated themselves.

The results of their finding were presented on Thursday, August 23, 2007, at the European Planetary Science Congress in Potsdam, Germany. Their findings also appear in Science Express, the Internet version of Science magazine,

Previously, astronomers thought that the rings of Uranus were pretty much unchanging. The process of adding and removing dust by natural causes cancelled out any noticeable changes, at least, any change that could be seen here on the Earth. However, with these improved imaging systems, de Pater’s team now realizes that major changes occur within the rings. Already they have discovered that one ring (zeta) has disappears, while a new one has appeared.

They do not know yet what causes these changes although they conjecture that variations could be caused by pressure from solar radiation, drag forces from the magnetic field of Uranus, or from collisions with larger bodies such as meteoroids.

Based on this information and on information from the rings around Saturn, astronomers now think that such rings are very dynamic structures, continuously changing and evolving.

Uranus has nine major rings that are composed of rock. The planet also contains numerous small dust rings.

Dramatic images are available on the University of California, Berkeley website UCBerkeleyNews (“Keck, Hubble provide new view of Uranus' rings”). The website of Dr. de Pater contains comparisons of the rings taken in different years.

From the UCB website, the astronomers conclude: "With further observations, the time scales over which these variations occur should provide new insight into the physical processes at work."

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