We present observations of the occultation of Umbriel by Oberon on 2007 May 4. We believe this is the first observed mutual event between satellites of Uranus. Fitting a simple geometric model to the light curve, we measure the mid-event time with a precision of 4 s. We assume previously measured values for the albedos of the two satellites, and measure the impact parameter to be 500 +/- 80 km. These measurements are more precise than estimates based on current ephemerides for these satellites. Therefore observations of additional mutual events during the 2007-2008 Uranian equinox will provide improved estimates of their orbital and physical parameters.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2008
- planets and satellites: individual: Umbriel;
- planets and satellites: individual: Oberon;
- 4 pages, 3 figures, accepted for publication in MNRAS Letters