Minor Planet Designations

The choice of an appropriate name for a celestial body presents difficulties as the total number of objects increases rapidly and considerably. Eventually one is forced to introduce a numbering system. Very large numbers of objects, however, require the simultaneous use of numbers and names in order to avoid mistakes. In particular, minor-planet nomenclature requires such a procedure.

Until the middle of the nineteenth century, nomenclature problems did not exist. Ceres, Pallas, Juno, and Vesta were mentioned in scientific literature without associated numbers. They were handled the same way as the major planets known at the time. Problems only arose in about 1850 with the dramatic increase of minor-planet discoveries. It became customary to assign a special symbol to the name and number of a minor planet, following the custom of the traditional symbols associated with the major planets. This procedure, however, soon failed. On the one hand, it was difficult to print these symbols; on the other hand, it soon became impossible to remember all the different symbols assigned. It seems that Luther (1855) was the last astronomer who assigned a special symbol to a minor planet, namely to (37) Fides.

In place of symbols, the system of ordinal numbers was introduced. Ferguson (1852) initiated this development with (16) Psyche. He used an encircled number rather than setting the number in parentheses as is practiced today. Obviously, Ferguson adopted this style of designation from Encke (1851) who declared in the BAJ for 1854: "Endlich füge ich noch hinzu, daß bei der Verwickelung und Schwierigkeit der neueren Planetenzeichen ich mir erlaubt habe, statt der Zeichen Zahlen in einen Kreis eingeschlossen einzufuhren." [Finally, I want to add that - in view of the complications and difficulties with the recently used planetary symbols - I took the liberty to introduce encircled numbers instead of symbols. ] Wolf (1892) stated that he and Gould introduced the encircled numbers as early as 1851.

A number was assigned by the editor of the AN upon publishing the discovery of a minor planet. This custom soon resulted in awkward consequences. By the end of 1857, some fifty planets had been discovered -on October 9th Ferguson had detected (50) Virginia. The numbering, until then a chronological one, became confused because Goldschmidt had already found a new planet on September 9th, which was later named (56) Melete. This wasn't the first time the numbering method had been criticized. Laugier (1859) proposed that the numbering should be absolutely chronological. Indeed, new discoveries were given names very soon, but as for the number, the chronological order was to be followed strictly. Foerster (1861) gave a rather sarcastic outline of this policy of the Berliner Astronomisches Jahrbuch (BAJ): "Was die Benennungen der Planeten betrifft, so werden dieselben von Berlin aus vom Planeten (60) an nur mit Nummern bezeichnet werden ... Die Namensgebung konnte fortan nur eine Quelle von Lacherlichkeiten werden." [As for naming planets, Berlin defines them by numbers only from planet (60) onwards ... The naming process could become a source of ridicule.]

The problems of nomenclature and numbering were further complicated by the question of who was the true discoverer and who had the right to propose a name and act as the 'patron.' Wolf (1859) wrote a noteworthy comment: "So wenig man Flamsteed die Entdeckung des Uranus, oder Lalande die Entdek-kung Neptun's zugeschrieben hat, so wenig darf man Goldschmidt die Entdeckung von (56) zuschreiben, -nicht wer zuerst gesehen oder beobachtet, sondern wer zuerst erkannt hat, ist der Entdecker." [The discovery of Uranus cannot be ascribed to Flamsteed, the one of Neptune not to Lalande, accordingly you cannot ascribe the discovery of (56) to Goldschmidt, - the discoverer of a planet is not the one who first saw or observed it, but the one who first recognized it as a new object.] This was the first time that the patronage of a new discovery could be transferred to the person who computed the orbit if the first observer had not realized the nature of the object. Nowadays, this problem remains of some importance.

The sharp increase in discovery rate mandated that the BAJ or the AN assign numbers promptly. Although the basic idea of chronological numbering remained, other deficiencies in the nomenclature system soon emerged. In quite a few cases subsequent confirming observations of a 'discovery' could not be made; hence the number of spurious minor planets accumulated. What should then be done with the numbers which had been assigned to them? Tietjen, then editor of the BAJ, proposed a way out of this dilemma. Krueger (1892) had suggested that all subsequent new discoveries should be given a provisional designation: "...der Herausgeber der Astronomischen Nachrichten wird die neuen Planeten von jetzt an zunächst nur mit einer provisorischen Bezeichnung, 18.. A, B, C, ..., nach dem Datum der Anmeldung bei der Centralstelle fuär Astronomische Telegramme versehen. Die defini-

or or or

(2) Pallas

(5) Astraea





(12) Victoria1


(14) Irene


(16) Psyche

(17) Thetis


(29)Amphitrite (26) Proserpina2 (35) Leukothea (37) Fides

1 The given name Clio was changed into (12) Victoria. The erroneously assigned name (32) Pomona was changed into (26) Proserpina.

or or or or


The minor planet symbols are adopted from Webster's A Dictionary of the English Language, G. & C. Merriam & Co., Springfield, MA, USA, p. 1780 (1884). (Courtesy of R. W. Sinnott, Cambridge, MA, USA)

tive Numerierung wird der Herausgeber des Berliner Astronomischen Jahrbuchs erst spater zu geeigneter Zeit vornehmen und hierbei alle diejenigen Planeten, bei denen ein genügendes Material zur Berechnung der Bahnelemente nicht vorhanden sein sollte, von der Numerierung ausschließen." [From now on, the editor of the AN will first give the new planet a provisional designation, 18.. A, B, C, ..., according to the date of registration at the Central Bureau for Astronomical Telegrams. The definitive number will be given only later by the editor of the BAJ. This procedure will make it possible to exclude all planets from numbering whose orbital elements could not be calculated due to a lack of material.] Only one year later, in 1893, it was realized that one single capital letter in the provisional designation was not enough, so it was decided to start at the beginning of the alphabet again. That is, 1893 Z was followed by 1893 AA, 1893 AB, and so on. Krueger (1893) noted that the assignment of the letter should be done without respect to the interruption by the beginning of a new year. During World War I some additional systems for provisional designations were introduced, raising new problems. For example, the astronomers in Simeis did not have a regular transmission line during this time, and found it necessary to introduce their own provisional numbering.

The solution of the designation problem goes back to a suggestion by Bower (1924) and this system is still in use: "To produce homogeneity of nomenclature, the following suggestion is made. Assign as a provisional designation, the year of discovery and two capital letters. The first letter will indicate the time in the year of discovery; A, the interval Jan. 1-15, B Jan. 16-31, C Febr. 1-15, D Febr. 16-29, etc. The second letter will indicate the order in the discovery interval that notice came to the Recheninstitut; A = first, B = second, etc. This designation is of the same brevity as the one most used, accurately indicates time of discovery, approximately indicates the right ascension at discovery, and has a sufficient expansibility to make unnecessary more than one system of designation." The Berlin Recheninstitut adopted this suggestion and, since 1925, has acted accordingly. Kopff (1924) suggested the following refinement to the system of Bower: "Diese Vorschlage sind noch dahin zu erganzen, daß bei Entdek-kung von mehr als 25 Planeten in einem halben Monat, ein Fall, der allerdings kaum vorkommt, das Alphabet an zweiter Stelle von neuem wieder zu laufen beginnt unter Hinzufiigung des Index 1, 2 ... an den zweiten Buchstaben; so wäre z.B. der 26. Planet in der ersten Januarhalfte 1925 mit 1925 AAi, der 27. mit 1925 ABi, der 51. mit 1925 AA2 zu bezeichnen." [These suggestions are to be complemented as follows: In the improbable case (sic! ) of more than 25 discoveries within half a month, the alphabet for the second letter starts running once more followed by an index number; so the 26th planet in the first half of January

1925 should be designated 1925 AAX, the 27th planet 1925 ABX, the 51st planet 1925 AA2.] In this way the demand for a chronological ordering was finally met. This dictionary lists the principal designations following the new-style system with any entry.

In the course of time, a permanent number was given only if a certain number of observations, appropriately distributed over time, was assured. The ARI assigned a definitive number in practically all cases if a first elliptical orbit from three observations yielded sufficiently small residuals for all observations not taken into account. Herget (1952) sharpened these conditions considerably: "An unnumbered minor planet will be assigned a permanent number when elements have been derived which: a) depend upon observations in at least two oppositions, b) include perturbations, and c) produce satisfactory residuals for all known observations. Condition a) will not be required if the perihelion distance is less than 1.67 a.u." During the decades following Herget's refinements, the conditions became even stricter. Except for very unusual, earth-approaching planets, observations from three oppositions were demanded, including one longer-observed arc in one opposition. After having numbered a new record of 384 minor planets in 1990, Marsden (1991) even announced: "However, the general increase in the accuracy of the orbits of the numbered minor planets would seem to dictate that the standards for new numberings should be more stringent than hitherto. Although earth-approaching objects may be numbered after two oppositions and uniformly well-observed objects after three, it seems not unreasonable generally to delay numbering until there are four or even more oppositions..." Precise quantitative guidelines are discussed by Marsden (1996).

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