The definitive discovery of the Uranian rings was made by astronomers James L. Elliot, Edward W. Dunham, and Jessica Mink on March 10, 1977, using the Kuiper Airborne Observatory, and was serendipitous. They planned to use the occultation of the star SAO 158687 by Uranus to study the planet's atmosphere. When their observations were analysed, they found that the star disappeared briefly from view five times both before and after it was eclipsed by the planet. They deduced that a system of narrow rings was present. The five occultation events they observed were denoted by the Greek letters α, β, γ, δ and ε in their papers. These designations have been used as the rings' names since then. Later they found four additional rings: one between the β and γ rings and three inside the α ring. The former was named the η ring. The latter were dubbed rings 4, 5 and 6—according to the numbering of the occultation events in one paper. Uranus's ring system was the second to be discovered in the Solar System, after that of Saturn.