Data Set Overview
      =================
      During the period 1985-1990, the earth entered the orbital plane
      of Pluto and its moon Charon, and the mutual eclipse events were
      observed from ground-based observatories.  A subset of these data
      are included in this data set, and more will be added in future
      updates.  The current version contains photoelectric photometry
      data from thirty-nine events observed at Mauna Kea Observatory by
      Tholen, and CCD photometry data from fifteen events observed at
      Palomar Observatory by Buratti and colleagues.
 
      Data
      ====
      The Mauna Kea data is in the file pcmemko.tab, and includes
      standard B magnitudes and errors, and Julian date at mid-
      observation, corrected for light-travel time.  The Palomar data is
      in the file pcmepal.tab, and includes differential magnitudes and
      errors, and Julian date at mid-observation (uncorrected).
 
      Modification History
      ====================
      In January 2002 SBN personnel calculated UTC based on the Julian
      dates provided and added it to the data files. At the time
      resolution of the Julian date (less than 1.e-05), UTC and UT are
      equivalent. START_TIME and STOP_TIME values were updated
      throughout as appropriate. No other data values were changed.

Review
      ======
      This version of the data set underwent formal external review on
      May 10, 2002.
 
      Data Coverage and Quality
      =========================
      The data set is eventually intended to be a complete collection of
      groundbased observations of the Pluto-Charon mutual events.  At
      present, it contains visual photometric data from Mauna Kea
      Observatory and Palomar Observatory.  Additional data will be
      added in future updates.