I posted this question on the space exploration SE but people recommended that it would be more on-topic here. Could someone please help by giving some definite laws of nomenclature for celestial objects, like the provisional names given before a proper name is decided... I am copy-pasting the question here:

I tried searching the answer to this on Google for hours and visited the IAU website as well, but it didn't really clarify my doubt. I was reading about Black Widow Pulsar, which is an "eclipsing binary millisecond pulsar in the Milky Way" and after its common name, in brackets is given PSR B1957+20. How is this named? What nomenclature rules are used? Was this the provisional name given before it was named Black Widow Pulsar or is this the scientific name of the neutron star?

This is the case with most interstellar objects and stars. Like Ultima Thule has another name 486958 Arrokoth? Is this a scientific name? Please explain what nomenclature conventions are used to name the asteroids and stars.

  • 1
    $\begingroup$ In case you were not sure, 486958 Arrokoth is not an interstellar object. $\endgroup$
    – WarpPrime
    May 4, 2021 at 16:32
  • 1
    $\begingroup$ Have you read at this site? iau.org/public/themes/naming $\endgroup$ May 4, 2021 at 17:03

3 Answers 3


Names are common enough for solar system bodies, but generally stars don't have names, they have identifiers from various catalogues.

In the case of Pulsars. they are named by their location in the sky. Just like Earth has longitude and latitude, every point in the sky has a "right ascension" and "declination". Due to the slow movement of the Earth's axis, to identify the location in the sky you also need to mention a date, though you can look up the positions of stars in 1950 (B1950) or 2000 (J2000). Also, for historic reasons, the angle of right ascension (or "longitude") is measured in hours and minutes (24hr = 360 degrees)

Now the Black Widow pulsar is located at 19hr 57 minutes of right ascension and +20 degrees of declination (in the B1950 coordinates). So its designation is PSR B1957+20.


The rules from the the IAU for official designations are posted neatly here. More casual names, like the Black Widow Nebula, are not standardized, as far as I know.

For astronomical objects outside of our own Solar System: the designation of astronomical objects beyond the Solar System should consist of at least two parts — a leading acronym and a sequence value.

1. An acronym is a code specifying the catalogue or collection of sources, conforming to the following rules, among others:
    It should consist of at least three characters (letters and/or numerals, avoiding special characters).
    The acronym must be unique.
    Acronyms should not be excessively long.
2. Sequence: a string of usually alpha-numerical characters that uniquely identify the source within the catalogue. Common values for the sequence are:
    Running number.
    Based on the coordinates of the object. Equatorial Coordinates shall always be preceded by J if they are for the standard equinox of J2000.0.

Naming stars and exoplanets follow similar rules, with some specifications.

EDIT: As @astrosnapper said in their comment, the 'B' in sequence of an IAU designation, for example in the case of the OP's object, refer to the earlier FK4-based B1950 reference framework.

Lastly, naming detections of gravitational waves by LIGO/Virgo is according to the date of detection: $GW[year][month][day]$. For example, GW190521 was detected on May 21st, 2019. Now that many detections are being made on the same day, number are added after an underscore to label to time of day of the detection.

  • 2
    $\begingroup$ Regarding the sequence part of the IAU rules: in the case of the OP's object, these coordinates are referred to the earlier FK4-based B1950 epoch hence the 'B' $\endgroup$ May 4, 2021 at 18:41
  • $\begingroup$ @astrosnapper Great point! $\endgroup$ May 5, 2021 at 0:37
  • $\begingroup$ The term "superevent" has nothing to do with there being multiple detections on one day. (LIGO uses multiple detection pipelines to search for gravitational wave events in its data stream, whenever a pipeline fine candidate this is labelled as an "event". Of course, in the case of a real astrophysical gravitational wave hitting the detectors, one expects multiple pipelines to flag that as an event. Consequently, the LIGO database will be populated with multiple events corresponding to the same gravitational wave. These are grouped in the database as a "superevent") $\endgroup$
    – TimRias
    May 5, 2021 at 13:57

Short answer:

Many stars and other objects beyond the Solar System have proper names, but the vast majority of listed objects have only designations in one or more catalogs, and the vast majory of all the billions or trillions of objects observable with modern instruments have not been listed in any catalog and have no designation.

Long Answer:

So how many catalogs of astronomical objects are there?

J.R.R. Tolkien wrote in the first chapter of The Hobbit:

Gandalf! If you had heard only a quarter of what I have heard abou thim, and I have heard only a very little of all there is to hear, you would be prepared for any sort of remarkable tale.

And if somone knew of only a quarter of the astronomical catalogs that I know of, and I know of only very few of the total number, they would know there is a large number of such catalogs. I will only mention a few.

Part One of Two: Star Names and designations.

There have been many thousands of cultures speaking thousands of languges on Earth. And most cultures had proper names for at least a few of the 6,000 to 8,000 stars which can be viewed by the naked eye from Earth.

I own a copy of a book Star Names Their Lore and Meaning by Richard Hinckley Allen, 1899, 1963. And you might think that it would be nice to have a little booklet listing the names of stars and constellations in various cultures and maybe ten or twenty pages long. Star Names Their Lore and Meaning has XIV pages of titles and introduction and 563 numbered pages.

There is a book The Stars of Jade by Julius D.W. Staal, about Chinese constellation and star names.

And no doubt there are many other sources for proper names of stars.

In 1603 johann Bayer published Uranometria, an atlas of the constellations. Most of the stars were marked with Bayer designations, consisting of a lower case Greek letter and the genitive case of the constellation name in Latin.

For the benefit of people unfamiliar with the Greek Alphabet, Bayer designations usually have the Greek letter spelled out: Alpha, Beta, Gamma, Delta, and so on down to Omega, when there are that many visible stars in the constellation. If there were more stars than Greek letters, Bayer used an uppercase "A" followed by lower case b, c, d, etc.

Bayer mostly lettered the stars in order of brightness as seen from Earth, but sometimes by position in the constellation.


Most stars visible from the northern hemisphere have Flamsteed designations from the 1712 and 1783 editions of Historia Coelestis Britannica.

Flamsteed designations for stars are similar to Bayer designations, except that they use numbers instead of Greek and Roman letters. Each star is assigned a number and the Latin genitive of the constellation it lies in (see 88 modern constellations for a list of constellations and the genitive forms of their names). Flamsteed designations were assigned to 2554 stars. The numbers were originally assigned in order of increasing right ascension within each constellation, but due to the effects of precession they are now slightly out of order in some places.


So many of the stars visible from the northern hemsphere now have proper names in various languages, Bayer designations, and Flamsteed designations.

And since then tens and hundreds of different star catalogs have been made. Stars in those catalogs are usually identified by the name or abbreviation of the catalog followed by the number of the star in the catalog. Of course many stars have designations designations in several different catalogs.

As a result the nearest stars to the Sun include:

Alpha Centauri & Proxima Centauri, Barnard's Star, Wolf 359, Lalande 21185, Luyten 726-8, Ross 154, Epsilon Eridani, Lacaille 9352, EZ Aquarii, Struve 2395, Groombridge 34, and so on.

Since 2016 the Working Group on Star Names of the Internatinal Astronomical Union has been approving official proper names for stars and has approved 336 proper names of stars by August 2018.


Part Two: Names and Designations of Deep Sky Objects.

Astronomers noted hazy patches of light in the sky.

French Astronomer Charles Messier was interesting in finding comets, so he made a list of hazy objects in the sky so he wouldn't mistake them fom comets, and published his list from 1774 to 1781. The various Messier objects he cataloged are designated as M1 through M110.

Other astronomers published catalogs of such cloudy or nebulous objects, including John Dreyer's New General Catalog of Nebulae and Clusters of Stars, 1888, followed by two Index Catalogs in in 1895 and 1908.

Most of the well known deep sky objects are in Dreyer's catalogs and are listed as NGC or IC followed by their numbers in the catalog.

As it turned out, the deep sky objects listed in those catalogs belong to several vastly differen types.

One type is diffuse nebulae, which are "clouds" of gas and dust in interstellar space, often many light years across. They include emission nebulae which are heated by stars and so emit light, reflection nebulae which reflect light from stars, and dark nebulae which block light from stars and nebulae beyond them.

Another type is planetary nebulae, which are shells of gas emitted from stars collapsing into white dwarf stars at the end of their evolution.

Another type is open clusters, clusters of young newly formed stars within star forming regions of a galaxy.

Another type is globular clusters, much larger clusters of usually older stars, that obit galaxies outside of the main bodies of those galaxies.

Another type is galaxies. Galaxies are vast associations of stars, star clusters, and dark matter, Many galaxies also have a lot of gas and dust.

Galaxies range in size from tiny dwarf galaxies which don't have many more stars than globular star clusters to supbergiant galaxies with millions of times as many stars.

The main types of galaxies are spiral, elliptical, and irregular.

And now that many types of deep sky objects are known, there are many catalogs listing only a single type of deep sky object.

So emission nebulae, reflection nebulae, planetary nebulae, supernova remnants, planetary nebulae, open clusters, globular clusters, stellar associations, dwarf galaxies, giant galaxies, spiral galaxies, elliptical galaxies, irregular galaxies, clusters of galaxies, superclusters of galaxies, cosmic radio sources, cosmic X ray sources, neutron stars, pulsars, black holes, quasars, et. etc. all have separate catalogs.

And any object listed in such a catalog should have its catalog designation, and many objects are listed in more than one catalog and have more than one catalog designation.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .