Astronomical naming conventions

In ancient times, only the Sun and Moon, a few stars, and the most easily visible planets had names. Over the last few hundred years, the number of identified astronomical objects has risen from hundreds to over a billion, and more are discovered every year. Astronomers need to be able to assign systematic designations to unambiguously identify all of these objects, and at the same time give names to the most interesting objects, and where relevant, features of those objects.

The International Astronomical Union (IAU) is the recognized authority in astronomy for assigning designations to celestial bodies such as stars, planets, and minor planets, including any surface features on them. In response to the need for unambiguous names for astronomical objects, it has created a number of systematic naming systems for objects of various sorts.

Stars

There are no more than a few thousand stars that appear sufficiently bright in Earth's sky to be visible to the

The IAU does not recognize the commercial practice of selling fictitious star names by commercial star-naming companies.^[3]

Proper names

Stars may have multiple proper names, as many different cultures named them independently. Polaris, for example, has also been known by the names Alruccabah, Angel Stern, Cynosura, the Lodestar, Mismar, Navigatoria, Phoenice, the Pole Star, the Star of Arcady, Tramontana and Yilduz at various times and places by different cultures in human history.

In 2016, the

The star nearest to Earth is typically referred to simply as "the Sun" or its equivalent in the language being used (for instance, if two astronomers were speaking French, they would call it le Soleil). However, it is usually called by its Latin name, Sol, in science fiction.

Named after people

There are about two dozen stars such as

With the advent of the increased light-gathering abilities of the telescope, many more stars became visible, far too many to all be given names. Instead, they have

In 1540, the Italian astronomer Piccolomini released the book De le Stelle Fisse (On the Fixed Stars) which include star maps of 47 constellations where he numbered the stars in magnitude order using latin letters.^[14]

Bayer designation

The

As the resolving power of telescopes increased, numerous objects that were thought to be a single object were found to be optical star systems that were too closely spaced in the sky to be discriminated by the human eye. This led to a third iteration, where numeric superscripts were added to distinguish those previously unresolved stars. Examples include Theta Sagittarii (θ Sgr) later distinguished as Theta¹ Sagittarii (θ¹ Sgr) and Theta² Sagittarii (θ² Sgr), each being their own (physical) star system with two and three stars, respectively.

Flamsteed designation

Black holes have no consistent naming conventions.

Other black holes, such as Cygnus X-1 – a highly likely stellar black hole, are cataloged by their constellation and the order in which they were discovered. A large number of black holes are designated by their position in the sky and prefixed with the instrument or survey that discovered them.^[15] Examples are SDSS J0100+2802 (where SDSS stands for Sloan Digital Sky Survey), and RX J1131−1231, observed by the Chandra X-ray Observatory.^[16]

Supernovae

Four historical supernovae are known simply by the year they occurred:

Since 1885, the letter-suffixes are explicitly assigned, regardless whether only one supernova is detected during the entire year (although this has not occurred since 1947). Driven by advances in technology and increases in observation time in the early 21st century, hundreds of supernovae were reported every year to the IAU, with more than 500 catalogued in 2007.^[17] Since then, the number of newly discovered supernovae has increased to thousands per year, for example almost 16,000 supernovae observations were reported in 2019, more than 2,000 of which were named by CBAT.^[18]

Novae

Constellations

The sky was divided into constellations by historic astronomers, according to perceived patterns in the sky. At first, only the shapes of the patterns were defined, and the names and numbers of constellations varied from one star map to another. Despite being scientifically meaningless, they do provide useful reference points in the sky for human beings, including astronomers. In 1930, the boundaries of these constellations were fixed by Eugène Joseph Delporte and adopted by the IAU, so that now every point on the celestial sphere belongs to a particular constellation.^[19]

Galaxies

Like stars, most

The brightest planets in the sky have been named from ancient times. The scientific names are taken from the names given by the Romans: Mercury, Venus, Mars, Jupiter, and Saturn. Our own planet is usually named in English as Earth, or the equivalent in the language being spoken (for instance, two astronomers speaking French would call it la Terre). However, it is only recently in human history that it has been thought of as a planet. Earth, when viewed as a planet, is sometimes also called by its Latin scientific conventional name Terra, this name is especially prevalent in science fiction where the adjective "terran" is also used in the way which "Lunar" or "Jovian" is for Earth's moon or Jupiter. The Latin convention derives from the use of that language as an international scientific language by the first modern astronomers like Copernicus, Kepler, Galileo, Newton and others and was used for a long time. This is why the later discovered bodies were also named accordingly. Two more bodies that were discovered later, and considered planets when discovered, are still generally considered planets now:

• Uranus, discovered by William Herschel in 1781
• Neptune, discovered by Johann Gottfried Galle in 1846 (based on prediction by Urbain Le Verrier)

These were given names from Greek or Roman myth, to match the ancient planet names—but only after some controversy. For example, Sir William Herschel discovered Uranus in 1781, and originally called it Georgium Sidus (George's Star) in honour of King

Starting in 1801,

Derived from

Some sixty years after the discovery of Pluto, a large number of large trans-Neptunian objects began to be discovered. Under the criteria of classifying these Kuiper belt objects (KBOs), it became dubious whether Pluto would have been considered a planet had it been discovered in the 1990s. Its mass is now known to be much smaller than once thought and, with the discovery of Eris, it is simply one of the two largest known trans-Neptunian objects. In 2006, Pluto was therefore reclassified into a different class of astronomical bodies known as dwarf planets, along with Eris and others.

Exoplanets

Currently, according to the IAU, there is no agreed upon system for designating exoplanets (planets orbiting other stars). The process of naming them is organized by the IAU Executive Committee Working Group Public Naming of Planets and Planetary Satellites. The scientific nomenclature for the designations usually consists of a proper noun or abbreviation that often corresponds to the star's name, followed by a lowercase letter (starting with 'b'), like 51 Pegasi b.^[20]

The lowercase lettering style is drawn from the IAU's long-established rules for naming binary and multiple star systems. A primary star, which is brighter and typically bigger than its companion stars, is designated by a capitalized A. Its companions are labelled B, C, and so on. For example,

Natural satellites

Earth's natural satellite is simply known as the Moon, or the equivalent in the language being spoken (for instance, two astronomers speaking French would call it la Lune). English-language science fiction often adopts the Latin name "Luna" while using the English "Moon" as a term for natural satellites in general in order to better distinguish the wider concept from any specific example. Natural satellites of other planets are generally named after mythological figures related to their parent body's namesake, such as Phobos and Deimos, the twin sons of Ares (Mars), or the Galilean moons of Io, Europa, Ganymede, and Callisto, four consorts of Zeus (Jupiter). Satellites of Uranus are instead named after characters from works by William Shakespeare or Alexander Pope, such as Umbriel or Titania.

When

• H = Mercury (Hermes)^[a]
• V = Venus
• E = Earth
• M = Mars
• J = Jupiter
• S = Saturn
• U = Uranus
• N = Neptune

After a few months or years, when a newly discovered satellite's existence has been confirmed and its orbit computed, a permanent name is chosen, which replaces the "S/" provisional designation. However, in the past, some satellites remained unnamed for surprisingly long periods after their discovery. See Naming of moons for a history of how some of the major satellites got their current names.

The Roman numbering system arose with the very first discovery of natural satellites other than Earth's: Galileo referred to the Galilean moons as I through IV (counting from Jupiter outward), in part to spite his rival Simon Marius, who had proposed the names now adopted, after his own proposal to name the bodies after members of the Medici family failed to win currency. Similar numbering schemes naturally arose with the discovery of moons around Saturn and Mars. Although the numbers initially designated the moons in orbital sequence, new discoveries soon failed to conform with this scheme (e.g. "Jupiter V" is Amalthea, which orbits closer to Jupiter than does Io). The unstated convention then became, at the close of the 19th century, that the numbers more or less reflected the order of discovery, except for prior historical exceptions (see the Timeline of discovery of Solar System planets and their moons).

Geological and geographical features

In addition to naming planets and satellites themselves, the individual geological and geographical features such as craters, mountains, and volcanoes, on those planets and satellites also need to be named.

In the early days, only a very limited number of features could be seen on other Solar System bodies other than the Moon. Craters on the Moon could be observed with even some of the earliest telescopes, and 19th-century telescopes could make out some features on Mars. Jupiter had its famous Great Red Spot, also visible through early telescopes.

In 1919, the IAU was formed, and it appointed a committee to regularize the chaotic lunar and Martian nomenclatures then current. Much of the work was done by

The Martian nomenclature was clarified in 1958, when a committee of the IAU recommended for adoption the names of 128

Initially, the names given to minor planets followed the same pattern as the other planets: names from Greek or Roman myths, with a preference for female names. With the discovery in 1898 of the first body found to cross the orbit of Mars, a different choice was deemed appropriate, and 433 Eros was chosen. This started a pattern of female names for main-belt bodies and male names for those with unusual orbits.

As more and more discoveries were made over the years, this system was eventually recognized as being inadequate and a new one was devised. Currently, the responsibility for naming minor planets lies with the Working Group Small Bodies Nomenclature (WGSBN, originally the Committee Small Bodies Nomenclature, CSBN, and before that the Minor Planet Names Committee, MPNC), which is composed of 15 members, 11 of whom are voting members, while the other four are representatives for the

Whimsical names can be used for relatively ordinary asteroids (such as 26858 Misterrogers or 274301 Wikipedia), but those belonging to certain dynamical groups are expected to follow more strictly defined naming schemes.^[22][24]

• perihelion larger than 1.15 au
  ) may receive non-mythical names.
• Lagrangian point L₄ are named after Greek characters (such as 588 Achilles), whilst asteroids at L₅ are named after Trojans (such as 884 Priamus). Small Jupiter trojans with absolute magnitudes fainter than 12 (in the V band) can be named for Olympic athletes.^[22][28]
• Centaurs (such as 2060 Chiron) crossing or approaching the orbit of a giant planet, but not in a stabilizing resonance are named for the creatures, part horse and part man, from Greek mythology.
• Neptune trojans (objects in a 1:1 orbital resonance with Neptune, such as 385571 Otrera) are named for Amazons, with no differentiation between objects in L₄ and L₅.^[22][29]
• Plutinos (such as 90482 Orcus) are named after mythological figures associated with the underworld.
• Other trans-Neptunian objects (such as 50000 Quaoar), including classical Kuiper belt objects, are given mythological or mythic names (not necessarily from Greek or Roman mythology), particularly those associated with creation.

Comets

The names given to

Some comets were first spotted as minor planets, and received a temporary designation accordingly before cometary activity was later discovered. This is the reason for such comets as P/1999 XN120 (Catalina 2) or P/2004 DO29 (Spacewatch–LINEAR). The MPECs and HTML version of IAUCs, because of their telegraphic style, "flatten out" the subscripts, but the PDF version of IAUCs^[35] and some other sources such as the Yamamoto Circulars and the Kometnyj Tsirkular use them.

See also

Footnotes

References