IAU Standardizes 212 Traditional Star Names

Bringing order to chaos, the International Astronomical Union has approved standardized spellings and designations for the traditional names of 212 bright stars.

Ursa Major from Urania's Mirror

Ursa Major from Urania’s Mirror. 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. 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.

In a series of resolutions from 1922 to 1930, the International Astronomical Union approved standard spellings, abbreviations, and definitions for the 88 official constellations. Before this reform, several other constellations were recognized by some but not all astronomers: for instance, Quadrans Muralis, now preserved only in the name of the Quadrantid meteor shower. Even for the universally recognized constellations, there was no consensus where one stopped and another started. That caused grave problems with respect to newly discovered variable stars, because variable-star designations need to name the constellation that the star is in.

The IAU constellation reforms were wildly successful, and there was widespread hope that a similar procedure could be applied to traditional star names such as Sirius, the brightest star in the night sky. But that did not happen, for many reasons.

First, there was no urgent need among professional astronomers, because all the stars with traditional names also have official designations. Sirius, for instance, is unambiguously designated as Alpha Canis Majoris.

Second, whereas 88 constellations suffice to tile the entire sky, the star-naming problem is open-ended. Several thousand stars are visible to the unaided eye, and millions more are visible through modest-sized telescopes. No way are all of those going to get colloquial names -- but where to stop?

Finally, the star-name situation was far more chaotic than the constellations before the IAU reforms. The Yale Bright Star Catalog lists approximately 900 names that have been used at one time or another for approximately 400 stars. Most of those stars have multiple names, and a fair number of names have been applied to multiple stars. What a mess!

A New Standard for Star Names

The IAU has now created order out of this chaos, giving official status to 212 of these names. That brings the total number of IAU-approved star names to 227, including:

With any luck, the IAU's standardization of star names will prove as successful as the constellations it standardized almost a century ago. Expect the myriad conflicting usages in popular books and magazines to converge toward the IAU names over the next several years. I am delighted to report that the IAU's 212 is almost identical to the 224 star names currently listed in the Sky & Telescope Stylebook; we will only need to change our usage in six cases.

Persian illustration of Pegasus constellation with star names labelled

The Persian astronomer Abd al-Rahman al-Sufi depicted Pegasus in his influential star atlas, and this copy was made around 1435 for the Samarkand astronomer-ruler Ulugh Beg. The constellation is shown as depicted on a celestial globe (i.e. mirrored as seen in the night sky). The four brightest stars, forming the easily recognisable "Square of Pegasus" visible in the autumn and the winter night skies, are labelled Matn al-Faras ("The Horse's Back"), Mankib al-Faras ("The Horse's Shoulder"), Surrat al-Faras ("The Horse's Navel") and Jinah al-Faras ("The Horse's Wing"). The IAU has adopted the names for these stars that were in common use in recent centuries: Markab, Scheat, Alpheratz, and Algenib. The modern constellation Pegasus also contains the star designated 51 Pegasi, which hosts the first exoplanet discovered around a solar-type star. As a result of the IAU's NameExoWorld contest, the star is now named Helvetios and its planet, designated 51 Pegasi b, is named Dimidium.
Bibliothèque nationale de France, Paris / IAU

Why hasn't this been more of a problem in the past? Largely because most of these "popular" star names aren't really all that popular — and never have been. The name Sirius has been in continuous use with minor spelling variations for more than two millennia, but that's a rare exception. Roughly half the star names in the IAU list, while traditional sounding, were in fact invented after 1800. There was never a time when everyday people knew hundreds of stars by name — these "traditional" names are almost certainly used more widely today than ever before.

So there's no need to go out and memorize the IAU 212. I count just 18 star names that are universally recognized by amateur and professional astronomers, and all of these have been standardized, or nearly so, for 100 years. They are Aldebaran, Altair, Antares, Arcturus, Betelgeuse, Canopus, Capella, Castor, Deneb, Fomalhaut, Polaris, Pollux, Procyon, Regulus, Rigel, Sirius, Spica, and Vega.

If you can point out all 18 of these stars in the sky, you can pat yourself on the back and call yourself a highly educated stargazer. (Caveat: some of them are never visible if you live too far north or south of the equator.) But if you're curious about the meanings and derivations of the IAU 212 and many others, the recognized authority in the English language is A Dictionary of Modern Star Names by Paul Kunitzsch and Tim Smart.

Contributing editor Tony Flanders wrote the appendix on star names in the Sky & Telescope Stylebook.

14 thoughts on “IAU Standardizes 212 Traditional Star Names

  1. Frank-ReedNavigation.comFrank-ReedNavigation.com

    A few of the approved star names are annoying coinages created in the mid-20th century so that celestial navigators could have “common names” instead of Bayer labels. So “gamma Crucis” became “Gacrux”, and “alpha Trianguli Australis” became “Atria”. These clumsy coinages just roll of the tongue… much as peanut butter rolls off the tongue. But they meet the standard that the IAU working group set for themselves, and they do have some decades of usage history. All of the 57+1 navigational stars, traditional since the middle of the 20th century, are now on the IAU-approved list with only one spelling change, Alnair.

    Another pair of coined names has survived the test of time: Sualocin and Rotanev (backwards spellings of Nicolaus Venator, the latinized name of Sicilian astronomer Niccolo Cacciatore added to star charts c.1815) proving that even a prank can become official in astronomy if it lingers long enough! Alas, the star names Navi, Dnoces, and Regor (named from nicknames of the Apollo 1 astronauts with the same reverse-spelling trick), famously featured on Sky & Telescope star charts for many years after the Apollo missions, did not make it. While there’s a slim chance Navi and Regor might yet be approved, Dnoces already has an approved common names on the IAU list: Talitha.

    By the way in the article, you wrote, “There was never a time when everyday people knew hundreds of stars by name.” Very true, and also true of celestial navigators. While it’s an entertaining challenge to memorize all of the 57 navigational stars from the traditional (late 20th century) list, only those with time to kill get around to it. Historically in navigation, learning star names was so rare that Richard Henry Dana in “Two Years Before the Mast” c.1835 marveled of a captain who “knew
    every lunar star in both hemispheres”. Yep… every lunar star! All nine of them. That was counted as knowing a lot of stars by name among mariners in the early 19th century.

    Frank Reed
    Clockwork Mapping / ReedNavigation.com
    Conanicut Island USA

    1. Frank-ReedNavigation.comFrank-ReedNavigation.com

      In the article, you listed 18 stars that are “universally recognized by amateur and professional astronomers.” And that’s a solid list. The only notable exception, one of the ten brightest stars, is Achernar. Since it is so far south, like Canopus, many observers in mid-northern latitudes have never seen it.

      Of course, the adoption of this official star list by the IAU immediately implies that there are, in fact, a few other very bright stars equally deserving of being known by “common name”. They are all in deep southern skies, too, and in a rather small area of the sky: Acrux, Gacrux, Mimosa, Hadar, Rigil Kentaurus. Though these are very bright stars, these names have seen little use except among celestial navigators, and even for that community they appeared primarily starting in the middle of the 20th century. Personally, I think they’re all pretty awful. Acrux and Gacrux? Gack they’re unpleasant. Mimosa? That’s champagne and orange juice: a cocktail, not a star. Hadar is the Horrible. And finally Rigil Kentaurus is an abomination. We all know it as Alpha Centauri, and that has *become* its common name. Even celestial navigators, who were supposed to be the main market of users for the clumsy “common name”, usually shortened it to “Rigil Kent” when they had to use it. Nobody loves it. Why codify it? Can we convince the IAU Working Group to retract a few of these more ridiculous common names?? Here’s my toast for New Year’s Eve: I raise my mimosa to the star named ALPHA CENTAURI!!
      …and Bully for Brontosaurus while we’re at it.


  2. Anthony BarreiroAnthony Barreiro

    I’m curious which six stars Sky and Telescope will need to rename.

    I’m familiar with all the common star names Tony lists above. For the past few months I’ve been studying celestial navigation (a long story that started with Bruce Watson’s article about the astrolabe in the February 2016 S&T). There are 58 named stars used in celestial navigation, most of which I don’t recognize by name. Having come in through astronomy, I’m much more familiar with Bayer designations.

      1. Jim-BaughmanJim-Baughman

        Come visit Los Angeles any time between the first week in October and the first week of April and on clear nights you can see Canopus blazing a low arc across the southern sky. Even in light-polluted LA it can be a fiery sight.

    1. JRJR

      Here you go, Anthony:

      Gamma Arietus
      S&T: Mesartim vs. IAU: Mesarthim

      Beta Ceti
      S&T: Deneb Kaitos vs. IAU: Diphda

      Alpha Gruis
      S&T: Al Na’ir vs. IAU: Alnair

      Beta Scorpii
      S&T: Graffias vs. IAU: Acrab

      Theta Scorpii
      S&T: Girtab vs. IAU: Sargas

      21 Tauri
      S&T: Sterope vs. IAU: Asterope

      1. Anthony BarreiroAnthony Barreiro

        Thanks JR. I will miss Deneb Kaitos. “Diphda” doesn’t tell me anything, but Deneb Kaitos tells me that I’m looking for the whale’s tail. And I’ve come to associate Graffias with Beta Scorpii. “Acrab” sounds like it should be in Cancer.

  3. Bill Walderman

    I know 17/18 (Canopus, which isn’t visible from my latitude, 39N, is the exception), and a number of others, too. Now that the list is official, I have a project to learn as many of the others that are visible at my latitude as I can.

  4. Jose Alberto-De Boni

    Looks like we are back to the dark ages of an anthropocentric universe. People living at high Northern latitudes ignoring what is below their line of sight. The list of 18 “universally recognized” stars has just one that is characteristic of the Southern sky. Surely we are a minority, but I am sure that for Australians, Newzealanders, South Africans, Argentinians, Chileans and Brazilians (like me) that list of 18 stars is not universal at all, letting out many jewels seen from the southern hemisphere. I propose you to enlarge this list to 24 stars: If you cannot point Acrux, Hadar, Mimosa, Menkent, Miaplacidus and Rigel Centaurus, I would not consider you an educated stargazer.


    So tonight’s task will be to observe all 18 stars in the “universally recognised” list. Here in Bahrain (at 25 deg N) I should be able to all 18 this evening once the sun has gone down. Only Antares might prove to be a problem. Let’s see if it can be done.

  6. Hindi

    I know 17 but have never seen Canopus since I live in the Sierra Foothills, north of latitude 40. And although Frank Reed indicates that navigators don’t memorize the navagational stars, I’m not a navigator but was an avid backpackpacker and so have memorized almost every constellation and almost every named star in the northern hemisphere visible without binoculars–just for the fun of it. I like to be able to lie on my sleeping bag at night, look up and be able to have those gorgeous names flow off my tongue: Kaffaljidhma, Vindemiatrix, Sadalmelik, Praecipua. Love those names! And maybe stave off dementia to boot!

  7. kellyon

    Thanks for the interesting article. I’m a big fan of astronomy. I also found info at http://solarstory.net/objects/milky-way that the name of the Milky Way is actually very ancient, ancient astronomers called our galaxy Milky Way when first viewing it because it resembled spilled milk. I want to buy a micro astronomical camera and hope to make some new photos of Milky Way in the near future.

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