Occultation observations reveal ring system around Uranus

Abstract

Much precise calculating and thorough planning went into preparations earlier this year for the first observed occultation of a star by the planet Uranus, but it was chance—and cautious allowance for chance—that led to the serendipitous discovery of five or more rings about the planet. Large uncertainties in the time at which the occultation would commence and in estimates of how far north it would be visible caused several observers to turn on their photometric equipment well in advance of the predicted moment—and only thus did they detect the unforeseen dips in the occulted star's light intensity that revealed Uranus as the second ringed planet in the solar system. Three groups promptly reported the unexpected dips, which they originally thought were caused by small Uranian satellites. James L. Elliot, Edward Dunham and Douglas Mink (Cornell University), aboard the flying Kuiper Airborne Observatory, saw brief occultations both before and after the star passed behind Uranus. Robert L. Millis and Lawrence H. Wasserman (Lowell Observatory) and Peter V. Birch (Perth Observatory, Western Australia) have reported similar pre‐immersion observations by Millis, Birch and Daniel Trout (Perth), and J. C. Bhattacharyya and K. Kuppuswamy (Indian Institute of Astrophysics) at Kavalur, Madras, also reported a single event. The Cornell group was the first to suggest that the brief occultations were due to thin rings—not small satellites—because the time intervals between their pre‐immersion and post‐emersion events were nearly equal.