In Search of Stellar Names

Star map painting by Senior Wardaman Elder Bill Yidumduma Harney, featuring the Milky Way, the Moon, and ancestor spirits. (Bill Yidumduma Harney)

Ursa Major, the constellation of the Great Bear, from Urania’s Mirror, a colourful set of constellation cards published by Samuel Leigh in England in 1824. Over the years, the star at the end of the tail has been known by two popular names, Alkaid and Benetnasch. On this card it is called Benetnasch, but the IAU Working Group on Star Names (WGSN) has chosen the more common alternative of Alkaid as its official name. Among the star names on this 1824 map of Ursa Major that are recognised by the IAU as official proper names are Alcor, Alioth, Dubhe, Megrez, Merak, and Mizar.  Other names on this map have been included in a growing database of cultural and historical names for stars, and some of these may eventually be adopted as official IAU names after further research and deliberation by the WGSN. (IAU)

The IAU has long differentiated proper names (e.g., Vega) from alphanumeric designations (e.g., “HR 7001”). While all catalogued stars and exoplanets have designations, until recently only a few hundred stars had common names. Similarly, only about thirty exoplanets had names. These were adopted through the 2015 IAU NameExoWorlds public naming campaign. Designations are a necessity of modern astronomy, often encoding valuable information about sky position, discovery technique, or discovery order. However, “names” usually win out over alphanumeric “designations” as being the more memorable. I polled the room of Division C IAU members last Friday and when asked how many people knew what “Fomalhaut” was, every hand shot up. When I asked if anyone knew its “HD” designation, not a single hand went up. While the ancient names of stars seem like anachronisms, they carry value as unique identifiers used by both scientists and the public. Astronomers are regularly reminded by the public that they prefer proper names to designations, and their use could ease communication. Proper names never “replace” designations, which remain useful aliases for research purposes. However, people tend to remember their friends and places by their names, not their phone numbers, postal codes, or geodetic coordinates. While certainly not every exoplanet or star may be worth a “name,” undoubtedly many are noteworthy enough to warrant a good one.

In the course of the exploration of the solar system, the necessity arose for IAU working groups to develop guidelines for the naming of planetary satellites, asteroids, and their surface features. The process has not been without growing pains. However, astronomers need only look at the elegance of the naming themes and cultural diversity represented among the recently named surface features of Ceres and Vesta found via imagery from the NASA Dawn mission to appreciate the efficacy of having IAU oversight on naming. To see examples of what “wild west” naming looks like without IAU guidelines, one may turn to the Mars map at where names are sold and anything goes. I’ll take IAU guidelines over ‘Boaty McBoatface’ any day.

It is hard to believe, but the first exoplanet was only discovered three decades ago.  The number of known exoplanets is pushing 3800, with 70% of these discoveries coming from the NASA Kepler spacecraft alone, and the number has roughly doubled every two and a half years. With new space observatories like TESS, Gaia, WFIRST, and PLATO, supported by ground-based radial velocity and transit surveys, that trend should continue through the 2020s. For centuries, philosophers and scientists have dreamt of a plurality of exo-terrae incognitae. The current generation of astronomers is discovering them and placing our planet in its proper cosmic perspective. Robotic reconnaissance of the solar system’s planets has made them places in the public imagination, inviting further exploration. The planets have been commemorated with songs, art, stamps, and toys, and their mythological names are familiar to all. Exoplanetary systems are becoming not only familiar to scientists, but to the public. Some exoplanets and their host stars are becoming worthy of memorable names rather than alphanumeric designations.

The 2015 NameExoWorlds campaign was assigning new names for exoplanet host stars “unless they already had well-known historic popular names.” What constituted well-known? Which names? Which spellings? It became apparent that previous IAU policy on proper names for stars was ambiguous. The IAU Style Manual (approved by XXth General Assembly) acknowledges star names, but multiple sources are cited, none as authoritative. The stars often had multiple names, conflicting spellings, and there were instances of the same name being used for multiple stars!

Shouldn’t the IAU recognize cultural star names from outside the pool of “traditional” Latinized Arabic/Greek names? If one of the IAU’s longstanding goals was to preserve astronomical heritage, including intangible heritage, why not incorporate cultural celestial names into the modern nomenclature of stars and exoplanetary systems? A new working group was needed to investigate and implement the idea.

The Division C WG Star Names (WGSN) was approved by the IAU Executive Committee in early 2016. WGSN’s activities are to

  1. establish IAU guidelines for the proposal and adoption of names for stars,
  2. search the international astronomical history and astronomical culture literature for star names,
  3. drawing upon this literature, adopt unique names for stars of scientific and historical value for community use following agreed upon guidelines, and
  4. assemble, maintain, publish, and disseminate an official IAU star name catalogue of names for stars and exoplanets.

The WGSN has completed a very productive past two years, and its catalog of star names is maintained at and its triennial report is posted on the WGSN IAU website. Since 2016, WGSN has converged on guidelines for stellar proper names, reviewed names from over 140 references, and adopted unique IAU names for 336 stars. For the most common ~200 or so “traditional” names, the most common name and spelling appearing in astronomical literature over the past century or two was adopted. Following NameExoWorlds, WGSN has decided to assign names to individual stars rather than unresolved multiples. Lettered component nicknames like “Sirius B” are considered as informal designations and are not catalogued by WGSN.  

The list of IAU unique star names includes approximately 40 cultural names from outside the pool of “traditional” names. These include names of Hindu, Persian, Yucatec Mayan, Chinese, French, Coptic, and various Polynesian, Aboriginal and African astronomical traditions. Among the most recent names adopted for the IAU list include the Hawai’ian name “Paikauhale” (meaning “vagabond”) for the star designated Tau Scorpii. For the bright, previously unnamed star in the Southern Cross designated Delta Crucis, the name “Imai” from the Mursi people of northeast Africa was adopted. The name comes from the type of grass that grows along the banks of the Omo River, and which is flattened yearly by seasonal floods that typically start when “Imai” the star in Crux ceases to appear in the evening sky every August. The components of the Alpha Centauri triple system now have IAU proper names Rigil Kentaurus (A), Toliman (B), and Proxima Centauri (C).

The WGSN’s activities have helped prepare the IAU for future public naming campaigns for exoplanets and their host stars, and preserving the names from ancient skywatchers for modern use. This is just in time as the IAU recently announced a new NameExoWorlds campaign as one of the IAU100 flagship programs. In the coming triennium, WGSN plans to focus further on indigenous names, and publishing the various cultural star names and their etymologies.

The Working Group on Star Names (WGSN) consists of an international group of astronomers with expertise in stellar astronomy, astronomical history, and cultural astronomy that will catalog and standardise proper names for stars for the international astronomical community.