The provisional designation of comets and asteroids are similar to each other: they both follow a pattern set in 1925 by the Minor Planet Center of the IAU.
At first, astronomers strove to assign symbols to the minor planets:
Encke made a major change in the Berliner Astronomisches Jahrbuch (BAJ) for 1854, published in 1851; in that yearbook he took the liberty to introduce encircled numbers instead of symbols. This was not quite like today's scheme, however: he began the numbering with Astrea which was given the number (1) and went through (11) Eunomia. Ceres, Pallas, Juno and Vesta continued to be denoted by their traditional symbols. This innovation was immediately seized upon by the astronomical community at large. Gould, in 1852, proposed to use circles containing the number of the asteroid in the chronological order of its discovery.
The new symbolic system was designed to relieve the growing confusion and restore the original intent of the symbols: a quick shorthand way of referring to solar system bodies. In the BAJ for 1855, the numbering of the minor planets began with (5) Astrea and went through (15) Eunomia. Ceres through Vesta continued to be listed using their old symbols until the BAJ for 1867, published in 1864.
Three additional asteroids were nevertheless given symbols:
According to Webster's A Dictionary of the English Language, G. & C. Merriam & Co., Springfield (Ma), USA, p. 1780 (1884) (http://www.uni-heidelberg.de/zentral/ari/minor.planets/mp-signs.htm), four more asteroids were also given symbols:
- 16 Psyche A sugar loaf (?) crowned by a star
- 17 Thetis A siren (?) above a star
- 26 Proserpina (At first erroneously assigned the name 32 Pomona) A circle around a star with a handle sticking up (?)
- 29 Amphitrite An upturned crescent crowned with a star
There is no evidence that these symbols were ever used outside of their initial publication in the Astronomische Nachrichten. Several different notation and symbolic schemes were used during the latter half of the nineteenth century. The present form (number followed by name) is first found in the Astronomische Nachrichten (AN) for 1911.
Initially, new numbers were assigned by the editors of the 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 BAJ 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 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 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., again 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.
In the double-letter scheme it was not generally possible to insert new discoveries into the sequence once designations had been assigned in a subsequent 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 SimŽis 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 SimŽis and other observatories also existed in parallel.
The basis of the modern system retains features of the older system. The key components include:
- The year of the observation
- (a blank space)
- A letter indicating the half-month of discovery (see table, below)
- A number for a comet, a second letter for an asteroid (I omitted, but Z is used!)
- Comet numbers continue indefinitely, but for an asteroid, a peculiar subscripting notation continues, assuming the first pass through the alphabets had implicit subscript 0. The second pass through uses 1, third 2, etc.
Comets are prefixed with C/ D/ P/ X/ depending on the type of comet orbit (or if it is now e"x"tinct). Asteroids can be prefixed with A/ but usually are not.
|first half of month ||A=Jan ||C=Feb ||E=Mar ||G=Apr ||J=May ||L=Jun ||N=Jul ||P=Aug ||R=Sep ||T=Oct ||V=Nov ||X=Dec |
|second half ||B=Jan ||D=Feb ||F=Mar ||H=Apr ||K=May ||M=Jun ||O=Jul ||Q=Aug ||S=Sep ||U=Oct ||W=Nov ||Y=Dec |
In the year 2004, the first asteroid discovery of January 1 would be named 2004 AA. Then the naming continues through 2004 AZ, followed by 2004 AA1. Partly for technological reasons (ASCII limitations), the subscript is often "flattened out", so 2004 AA1 is written 2004 AA1. The next discovery is 2004 AB1, then 2004 AC1, etc. Eventually one could get to something like 2004 AA276, BUT only if the calendar date has not passed to January 16. At that point, the system jumps onward to 2004 BA.
The object known as "90377 Sedna" had the provisional designation 2003 VB12, meaning it was discovered in the first half of November 2003, and that it was the 302nd object (B->2 + 12*25 = 302) discovered during that time. 28978 Ixion, originally 2001 KX76, was discovered in the latter half of May 2001, and was the (X->23 + 76*25 = 1923) 1,923rd object discovered during that time.
Comet discoveries work similarly. 2004 A1 is the first comet of January 1-15. 2004 A2 is the second, and so forth.
Many objects originally seen as asteroidal may develop clear tails and become comets. In that case they retain their asteroid designation with two letters, but gain the comet prefix C/ D/ or P/ as appropriate.
Clearly the system isn't sorted well, so a 'translation' is used for indexing long lists. First, the year is written out using a single letter code for the century (18 = I, 19 = J, 20 = K, and so on; the first century would theoretically be 00 = A) and the last two digits in clear. Thus 2004 AA starts off as K04. Next, the implicit subscript becomes explicit and is inserted between the letters so the first pass sorts before the second pass. Thus 2004 AA becomes K04A00A, 2004 AA1 becomes K04A01A, and so on. The use of a two digit field (00 through 99) would have originally been enough, but in the late 1990's so many discoveries resulted that a hexadecimal-like notation had to be adopted for the tens, where A=10, B=11, etc. This first occurred with (17810) 1998 FM100. Thus 2004 AZ99 becomes K04A99Z and 2004 AA100 becomes K04AA0A. This can continue through Z=35, so 2004 AZ359 becomes K04AZ9Z - the highest possible packed designation in this scheme.
The beginning of the 2000's led to 360 passes through the alphabet requiring a further adaptation. This first occurred with (62643) 2000 SH360. The scheme adopted was to set a=36, b=37, etc. This also sorts well in ASCII but loses the all-capitals and might cause case problems. This system currently ends at the equivalent of 2004 AZ619 with z=61. The highest count reached as of 2004 was 2000 SA372. Thus, 2004 AA360 becomes K04Aa0A and 2004 AZ619 becomes K04Az9Z.
Comets are 'packed' similarly, but rarely create problems as the objects now are often discovered first appearing as asteroidal. They are packed such that a zero takes the place of the missing letter at the end. Thus 2004 A22 becomes K04A220. Were comet discoveries to "roll over" past 2004 A99 (K04A990), the same system would assign 2004 A100 as K04AA00 all the way to 2004 A619 as K04Az90.