• Preparing MPCs (Info)

  • New- And Old-Style Minor Planet Designations

    This document describes the formats for both new-style provisional designations for minor planets (as used from the start of 1925) and the old-style designations (as used prior to 1925).

    New-Style Provisional Designations

    The Minor Planet Center assigns new provisonal designations when it is in possession of at least two nights of observations of an object that cannot be identified immediately with some already designated object.

    The standard designation consists of the following parts, all of which are related to the date of discovery of the object: a 4-digit number indicating the year; a space; a letter to show the half-month; another letter to show the order within the half-month; and an optional number to indicate the number of times the second letter has been repeated in that half-month period.

    The half-month of discovery is indicated using the following scheme:

      Letter     Dates             Letter      Dates
        A      Jan. 1-15             B       Jan. 16-31
        C      Feb. 1-15             D       Feb. 16-29
        E      Mar. 1-15             F       Mar. 16-31
        G      Apr. 1-15             H       Apr. 16-30
        J      May  1-15             K       May  16-31
        L      June 1-15             M       June 16-30
        N      July 1-15             O       July 16-31
        P      Aug. 1-15             Q       Aug. 16-31
        R      Sept.1-15             S       Sept.16-30
        T      Oct. 1-15             U       Oct. 16-31
        V      Nov. 1-15             W       Nov. 16-30
        X      Dec. 1-15             Y       Dec. 16-31
                 I is omitted and Z is unused
    The order within the month is indicated using letters as follows:
        A = 1st     B = 2nd     C = 3rd     D = 4th     E = 5th
        F = 6th     G = 7th     H = 8th     J = 9th     K = 10th
        L = 11th    M = 12th    N = 13th    O = 14th    P = 15th
        Q = 16th    R = 17th    S = 18th    T = 19th    U = 20th
        V = 21st    W = 22nd    X = 23rd    Y = 24th    Z = 25th
                            I is omitted
    If there are more than 25 discoveries in any one half-month period, the second letter is recycled and a numeral `1' is added to the end of the designation. If more than 50 discoveries, the second-letter is again recycled, with a numeral `2' appended after the second letter. Discoveries 76-100 have numeral `3' added, numbers 101-125 numeral `4', etc. When possible, these additional numbers should be indicated using subscript characters.

    Thus the order of assignment of designations in a particular half-month period is as follows: 1995 SA, 1995 SB, ..., 1995 SY, 1995 SZ, 1995 SA1, ..., 1995 SZ1, 1995 SA2, ..., 1995 SZ9, 1995 SA10, etc.

    This scheme has been extended to pre-1925 discoveries--such designations are indicated by the replacement of the initial digit of the year by the letter `A'. Thus, A904 OA is the first object designated that was discovered in the second half of July 1904.

    Survey Designations

    Four special surveys, undertaken between 1960 and 1977, have designations that consist of a number (identifing the order within that survey), a space and a survey identifier. The survey identifiers are as follows:
       Survey                         Identifier
       Palomar-Leiden (1960)             P-L
       First Trojan Survey (1971)        T-1
       Second Trojan Survey (1973)       T-2
       Third Trojan Survey (1977)        T-3
    Example designations are 2040 P-L, 3138 T-1, 1010 T-2 and 4101 T-3.

    Old-Style Provisional Designations

    In the first half of the 19th century, minor planets were referred to simply by name. The assignment of ordinal numbers, ostensibly in order of discovery, was introduced in the early 1850s. Initially, new numbers were assigned by the editors of the Astronomisches Nachrichten (AN) immediately upon receipt of the announcement of a new discovery from an observer.

    In 1892 a system of provisional designations was introduced by the AN. A definitive number was subsequently given by the editors of the Berliner Astronomisches Jahrbuch to those objects for which reasonable orbital elements had been computed. The provisional designation scheme consisted initially of a year and a single letter: e.g., 1892 A, 1892 B, etc., omitting the letter `I'.

    In 1893, the 25 available letters proved to be insufficient and a series of double letter designations was introduced: e.g. 1893 AA, 1893 AB, etc., omitting the letter `I'. The sequence of double letters was not restarted anew each year, so 1894 AQ followed 1893 AP (for example). In 1916, the letters reached ZZ and, rather than starting a series of triple-letter designations, the double-letter series was restarted with 1916 AA.

    [NOTE: In old publications, it is common to see `J' as the omitted letter instead of `I'--the sequence going 1892 H, 1892 I, 1892 K, etc. Modern usage would consider 1892 I to be the same as 1892 J and it is this latter designation which is recorded.]

    In the double-letter scheme it was not generally possible to insert new discoveries into the sequence once designations had been assigned in a subsquent year. The scheme used to get round this problem was rather clumsy and used a designation consisting of the year and a lower-case letter in a manner similar to the old provisional-designation scheme for comets. For example, 1915 a (note that there is a space between the year and the letter in order to distinguish this designation from the old-style comet designation 1915a), 1917 b. In 1914 designations of the form year plus Greek letter were used in addition.

    During World War I the active observers at Simëis in the Crimea, deprived of official designations for their discoveries, assigned their own. The designations came in two forms: year + Greek capital sigma + letter(s); Greek capital sigma + number. The Greek capital sigma is indicated as SIGMA.

    Other designation schemes used at Simëis and other observatories are listed elsewhere.

    To summarise, the following forms of input are valid:

    • Year + Single Letter: 1892 A
    • Year + Double Letter: 1914 VV
    • Year + letter: 1913 a
    • Year + Greek letter: 1914 gamma
    • Year + SIGMA + letter: 1915 SIGMA r, 1916 SIGMA ci
    • SIGMA + number: SIGMA 27
    For the purposes of searching, SIGMA may be abbreviated to SIG and the year is optional on the year+SIGMA+letter designations (i.e., SIGMA ci is a shorthand form for 1916 SIGMA ci).