When two teams of scientists set up to watch Uranus pass in front of star SAO 158687 in 1977, they expected a rare chance to observe a distant planet. Instead, they made a major discovery: Uranus, like Saturn, is encircled with a band of rings.
As the observers in the Kuiper Airborne Observatory and the Perth Observatory in Australia watched, the star appeared to blink out briefly several times. The blinking was caused by the rings blocking the starlight. The Australian team was so surprised they missed three rings as they tried to figure out why the starlight signal kept disappearing.
The Kuiper team had a better vantage point and were first to publish the surprising news that Uranus was encircled by five narrow rings, which they named Alpha, Beta, Gamma, Delta and Epsilon in order of increasing distance from the planet. The Perth team identified six distinct dips in the starlight, which they named rings 1 through 6.
After careful analysis and a closer view courtesy of the Voyager 2 spacecraft in 1986, scientists have now identified 13 known rings around Uranus. [Editor's note: The discovery of two new rings was announced on December 22, 2005. See HubbleSite News Release Archive.] In order of increasing distance from the planet, they are 1986U2R, 6, 5, 4, Alpha, Beta, Eta, Gamma, Delta, Lambda, Epsilon, Nu and Mu. Some of the larger rings are surrounded by belts of fine dust.
Reference: USGS Astrogeology: Gazetteer of Planetary Nomenclature -- Ring Nomenclature