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  • Explanation Of Symbols

    The symbols used in the lists of unusual objects and on MPECs have the following meanings (for detailed descriptions of what the meanings mean, you are referred to standard texts on celestial mechanics):
    Designation (and name)
    For numbered minor planet, this column contains the object's number and name (if named).
    Prov. Des.
    This is the object's provisional designation. Note that some of the low-numbered objects have old-style provisional designations, where the letters were recycled without regard to the calendar.
    Ln
    For Trojans, this column indicates whether the minor planet is near the L4 or the L5 point of the planet. L4 is 60° preceding the planet and L5 is 60° following.
    q
    Perihelion distance (in AU).
    Q
    Aphelion distance (in AU).
    EMoid/Earth MOID
    The value (in AU) of the Earth MOID. This is the minimum distance between the orbit of the earth and the minor planet. The MOID value is for the earth (not the earth-moon barycenter) and is for the epoch of the minor-planet orbit. Note that the MOID does not give any information on actual close approaches--you should refer to lists of close encounters for such information. A value less than the radius of the earth does NOT indicate that a hit will occur.
    H
    Absolute visual magnitude. A table converting H to a diameter range is available.
    Epoch, M
    These columns give the value of the mean anomaly for the specified epoch (in YYYYMMDD format).
    Peri., Node, Incl.
    The angular J2000.0 elements of the orbit, in degrees: argument of perihelion, longitude of the ascending node and inclination.
    e
    Orbital eccentricity.
    a
    Semimajor axis (in AU).
    Opps.
    Number of oppositions at which the object has been observed. If observations have been made at one opposition only, the arc length in days is given in parentheses.
    Ref.
    Reference to the published orbit, generally to the MPCs (= Minor Planet Circulars), MPOs (= Minor Planet Circulars Orbit Supplement) or Icarus.
    Types of Object
    NEAs are Near-Earth Asteroids. NEOs are Near-Earth Objects (including both asteroids and comets). The definitions for the various classes of NEA differ between different sources. Here, the following definitions are used: Atens have semimajor axes, a, less than 1 AU; Apollos have semimajor axes, a, greater than 1 AU, and perihelion distances, q, less than 1 AU; and Amors have perihelion distances between 1 and 1.3 AU.
    PHA
    PHAs are potentially-hazardous objects. These are objects with H brighter than V = 22 and an Earth MOID less than 0.05 AU.
    Some other quantities were given on older lists.
    M+, M-
    The perpendicular distance to the earth's orbit when an object is at the earth's distance from the sun (in AU, omitted if greater than 0.3 AU). These quantities are given only for objects with perihelion distances less than 1.05 AU, although they are physically meaningful only when the orbit of an object intersects that of the earth. For Amor objects with perihelion distances less than 1.05 AU, a single value spans the two columns. For more information on these quantities, see Marsden, B. G. (1993) To Hit Or Not To Hit. In Proceedings of the Near-Earth-Object Interception Workship, pp. 67-71. Eds. G. H. Canavan, J. C. Solem and J. D. G. Rather. Los Alamos National Laboratory.
    N+, N-
    The distances of an object's nodal points from the earth's orbit (in AU, omitted if greater than 0.3 AU). N+ refers to the distance from the ascending node, N- to the distance from the descending node. These quantities are only given for objects with perihelion distances less than 1.3 AU. For more information on these quantities see Marsden (1993, ibid.).
    Min.
    This quantity, in AU and given only in the list of the larger potentially dangerous minor planets, is the minimum value of N+, N-, M+ and M-. If the minimum value corresponds to one of the value of N, it is followed by a `D' (to denote that the minimum value occurs at the descending node) or by an `A' (to denote that the minimum value occurs at the ascending node). Note that quantity does not give any information on actual close approaches--you should refer to lists of close encounters for such information. A value of 0.000 does NOT indicate that a hit will occur.