Editing Astronomical naming conventions (section)

== Planets ==
{{see also|Definition of planet|IAU definition of planet}}

The brightest [[planet]]s in the sky have been named from ancient times. The scientific names are taken from the names given by the Romans: [[Mercury (planet)|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 language|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 (mythology)|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 [[George III of the United Kingdom]]. French astronomers began calling it Herschel before German [[Johann Bode]] proposed the name Uranus, after the Greek god. The name "Uranus" did not come into common usage until around 1850.

Starting in 1801, [[asteroid]]s were discovered between Mars and Jupiter. The first few ([[Ceres (dwarf planet)|Ceres]], [[2 Pallas|Pallas]], [[3 Juno|Juno]], [[4 Vesta|Vesta]]) were initially considered planets. As more and more were discovered, they were soon stripped of their planetary status. On the other hand, [[Pluto]] was considered to be a planet at the time of its discovery in 1930, as it was found beyond Neptune. Following this pattern, several hypothetical bodies were given names: [[Vulcan (hypothetical planet)|Vulcan]] for a planet within the orbit of Mercury; [[Phaeton (hypothetical planet)|Phaeton]] for a planet between Mars and Jupiter that was believed to be the precursor of the asteroids; [[Themis (hypothetical moon)|Themis]] for a moon of Saturn; and [[Persephone (hypothetical planet)|Persephone]], and several other names, for a trans-Plutonian planet.

Derived from [[Classical mythology]], these names are only considered standard in [[Western culture|Western]] discussion of the planets. Astronomers in societies that have other traditional names for the planets may use those names in scientific discourse. For instance, IAU does not disapprove of astronomers discussing Jupiter in [[Arabic language|Arabic]] using the traditional Arabic name for the planet, {{lang|ar|المشتري}} ''Al-Mushtarīy''.

Some sixty years after the discovery of Pluto, a large number of large [[trans-Neptunian object]]s 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 (dwarf planet)|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 planet]]s, along with Eris and others.

=== Exoplanets ===
{{Main|Exoplanet#Nomenclature}}

Currently, according to the IAU, there is no agreed upon system for designating [[exoplanet]]s (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]].<ref>{{cite web | url = http://www.iau.org/public/themes/naming_exoplanets/ | title = Naming of exoplanets | publisher = International Astronomical Union | access-date = 2014-12-01 }}</ref>

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, [[Sirius]], the brightest star in the sky, is actually a double star, consisting of the naked-eye visible Sirius A and its dim white-dwarf companion [[Sirius B]]. The first exoplanet tentatively identified around the second brightest star in the triple star system [[Alpha Centauri]] is accordingly called [[Alpha Centauri Bb]]. If an exoplanet orbits both of the stars in a binary system, its name can be, for example, [[Kepler-34(AB) b]].

=== Natural satellites ===
{{Further|Naming of moons}}

Earth's natural satellite is simply known as the [[Moon]], or the equivalent in the language being spoken (for instance, two astronomers speaking [[French language|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 (moon)|Phobos]] and [[Deimos (moon)|Deimos]], the twin sons of [[Ares]] (Mars), or the [[Galilean moons]] of [[Io (moon)|Io]], [[Europa (moon)|Europa]], [[Ganymede (moon)|Ganymede]], and [[Callisto (moon)|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 (moon)|Titania]].

When [[natural satellite]]s are first discovered, they are given provisional designations such as "[[Jupiter LII|S/2010 J 2]]" (the 2nd new satellite of Jupiter discovered in 2010) or "[[S/2003 S 1]]" (the 1st new satellite of Saturn discovered in 2003). The initial "S/" stands for "satellite", and distinguishes from such prefixes as "D/", "C/", and "P/", used for [[comet]]s. The designation "R/" is used for planetary rings. These designations are sometimes written like "S/2003 S1", dropping the second space. The letter following the category and year identifies the planet ('''J'''upiter, '''S'''aturn, '''U'''ranus, '''N'''eptune; although no occurrence of the other planets is expected, Mars and Mercury are disambiguated through the use of '''H'''ermes for the latter). [[Pluto]] was designated by '''P''' prior to its recategorization as a [[dwarf planet]]. When the object is found around a minor planet, the identifier used is the latter's number in parentheses. Thus, [[Dactyl (asteroid)|Dactyl]], the moon of [[243 Ida]], was at first designated "[[S/1993 (243) 1]]". Once confirmed and named, it became [[(243) Ida I Dactyl]]. Similarly, the fourth satellite of Pluto, [[Kerberos (moon)|Kerberos]], discovered after Pluto was categorized as a dwarf planet and assigned a minor planet number, was designated [[S/2011 (134340) 1]] rather than S/2011 P 1,<ref>{{cite web|url=http://www.cbat.eps.harvard.edu/cbet/cbet002769.txt |title=New Satellite of (134340) Pluto: S/2011 (134340) 1|access-date=2011-07-20 |url-status=dead |archive-url=https://web.archive.org/web/20120526133147/http://www.cbat.eps.harvard.edu/cbet/cbet002769.txt |archive-date=2012-05-26 }}</ref> though the ''[[New Horizons]]'' team, who disagreed with the dwarf planet classification, used the latter.
* '''H''' = [[Mercury (planet)|Mercury]] (Hermes){{efn|The assignment of "H" for Mercury is specified by the {{cite web |url=http://planetarynames.wr.usgs.gov/specifics.html |title=USGS Gazetteer of Planetary Nomenclature}}; since the USGS usually closely follows IAU guidelines, this is very likely the IAU convention, but confirmation is needed.}}
* '''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 Galilei|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 [[House of Medici|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&nbsp;V" is [[Amalthea (moon)|Amalthea]], which orbits closer to Jupiter than does [[Io (moon)|Io]]). The unstated convention then became, at the close of the 19th&nbsp;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 ===
{{main|Planetary nomenclature}}

In addition to naming planets and satellites themselves, the individual [[Lists of geological features of the Solar System|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 [[Mary Adela Blagg]], and the report ''Named Lunar Formations'' by Blagg and Muller (1935), was the first systematic listing of lunar nomenclature. Later, "The System of Lunar Craters, quadrants I, II, III, IV" was published, under the direction of [[Gerard P. Kuiper]]. These works were adopted by the IAU and became the recognized sources for lunar nomenclature.

The Martian nomenclature was clarified in 1958, when a committee of the IAU recommended for adoption the names of 128 [[albedo feature]]s (bright, dark, or colored) observed through ground-based telescopes (IAU, 1960). These names were based on a system of nomenclature developed in the late 19th century by the Italian astronomer [[Giovanni V. Schiaparelli]] (1879) and expanded in the early 20th century by [[Eugene M. Antoniadi]] (1929), a Greek-born astronomer working at [[Meudon]], France.

However, the age of [[space probe]]s brought high-resolution images of various Solar System bodies, and it became necessary to propose naming standards for the features seen on them.