• MPC Preparation (Info)


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    Read MPEC 2010-U19 Read MPEC 2010-U21

    M.P.E.C. 2010-U20                                Issued 2010 Oct. 19, 02:20 UT
         The Minor Planet Electronic Circulars contain information on unusual
             minor planets and routine data on comets.  They are published
       on behalf of Commission 20 of the International Astronomical Union by the
              Minor Planet Center, Smithsonian Astrophysical Observatory,
                              Cambridge, MA 02138, U.S.A.
             Supported in part by the Steven and Michele Kirsch Foundation
                 Prepared using the Tamkin Foundation Computer Network
              URL http://cfa-www.harvard.edu/iau/mpc.html  ISSN 1523-6714
                                   EDITORIAL NOTICE
         The rules defining who discovered a particular object have evolved over
    the past two centuries.  In the days of visual observation, discovery was
    credited to the first person to report an observation of a new object.  If
    a subsequent report emerged of an earlier observation, the discovery credit
    was switched to the earlier observer.  This reassignment of discovery credit
    was applied somewhat arbitrarily and there are a number of cases where
    earlier observations are simply listed as "prediscovery".  Designations would
    be assigned on the basis on single-night approximate measures.  When the Minor
    Planet Center (MPC) was founded, discoveries continued to be credited on the
    basis of single approximate positions (e.g., Minor Planet Circular 2).  After
    the MPC moved to Cambridge in 1978, an Editorial Notice (Minor Planet Circular
    4845-4846) informed observers that approximate observations were no longer
    eligible for discovery credit.  In 1995, the decision was taken to no longer
    assign designations to single-night detections (Minor Planet Circular 24597).
         The Minor Planet Center (MPC) recently changed the way discovery credit
    was assigned to new discoveries.  Rather than being the earliest observation
    in the initial two-night linkage, the discovery credit was to be given to
    the earliest observation at that opposition.  In practice, it is often
    difficult to determine which observation is the earliest at the time the
    designation needs to be assigned.
         Effective immediately, the MPC will separate the concept of discovery
    credit from the assignment of asterisks.  Asterisks will revert to being
    simply an indication of the initial assignment of a new designation and will
    not be associated with any discoverer.
         In addition, the MPC will begin adding timetags to all archived and
    newly-received observations, to indicate when they were received at the MPC.
    For the moment, these timetags will be maintained only on internal datasets.
    External availability of the timetags will depend on certain professional
    users of the observational datasets indicating that their software will cope
    with the extended format.  For newly-submitted observations, the timetags will
    indicate when the observation was accepted by the AUTOACK routine.  For
    previously-submitted observations, a timetag will be constructed that is
    related to the date of observation.  Known cases of delayed submission of
    observations will be accounted for in these constructed timetags.
         Discoverers will be defined only when an object is numbered.  At that
    time, the timetags on all the observations included in the solution will be
    examined.  The discovery observation will be that observation which is the
    earliest-reported observations at the opposition with the earliest-reported
    second-night observation.  The discovery observation will then define the
    discoverer.  This scheme, which will be entirely automatic, is consistent
    with the following resolution adopted by Commission 20 at the 1979 IAU
    General Assembly: "The Commission defines the discovery as the earliest
    apparition at which an orbit useful in the establishment of identifications
    was calculated" (taken from Minor Planet Circular 4845-4846).
         The new scheme removes one common complaint with the current scheme: that
    the assignment of discovery credit depended, to some degree, on the ability
    of either the MPC or the observer to make the initial night-to-night linkages.
    In addition, it removes the apparent arbitrary nature of the order of
    designations in new identifications.
        Objects that have multiple-opposition orbits as of now will be
    grandfathered into the old scheme of assigning discovery credit.
    Timothy B. Spahr             (C) Copyright 2010 MPC           M.P.E.C. 2010-U20

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