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 disovery: Uranus, like
, 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. More rings were discovered in 1986.
Observing distant planets is difficult, especially with complications
due to daylight arriving before the planet completed its transit in
front of the star. But, after careful analysis and a closer view
courtesy of the Voyager
spacecraft in 1986, scientists have now identified 11 known rings around
Uranus. In order of increasing distance from the planet, they are
1986U2R, 6, 5, 4, Alpha, Beta, Eta, Gamma, Delta, Lambda and Epsilon.
Some of the larger rings are surrounded by belts of fine dust.