Uranus: Ring System
The Uranian ring system was discovered by accident in 1977, during the observation of a stellar occultation (the passage of Uranus in front of a star). A symmetric pattern of sharp dips in the stellar signal on either side of the planet revealed the presence of at least five narrow, almost opaque rings (Elliot, Dunham and Mink, 1977; Millis, Wasserman and Birch, 1977). Subsequent occultations observed in the late 1970s and 1980s, both from Earth-based telescopes and with instruments on the Voyager spacecraft, led to the discovery of five additional rings, while providing an abundance of data on the radii, widths and transparencies of the rings (Elliot and Nicholson, 1984; Holberg et al., 1987; Gresh et al., 1989; Colwell et al., 1990). In order of increasing distance from Uranus, the ten rings are designated 6, 5, 4, α, β, η, γ, δ, λ and ε, the somewhat curious nomenclature reflecting the naming of the original five rings (α-ε) as well as later discoveries.