Historical story

Who puts labels on stars and planets?

Starry Night and Night Watch are the official names for a star and planet in the northern sky as of last December. They got the label with the help of the Dutch public. Who names the rest of the stars?

Since December 17, there has been a star called Happiness, the translation of the official name Gakyid in the language of Bhutan. And the star Coffee was also registered, at least the Ethiopian word Buna. There is even a star Franz around which planet Sissi orbits. And it would have been close if there had been a planet called Miffy.

In total, more than two hundred stars and exoplanets were renamed last month. The International Astronomical Union (IAU), which among other things deals with the naming of astronomical objects, was founded 100 years ago and decided to let the public of more than a hundred countries choose the name for a star and planet.

The Netherlands chose planet Miffy and star Mother Pluis. However, the responsible committee did not dare to register these names because they are registered trademarks. The choice then fell on Starry Night and Night Watch, after the two well-known Dutch paintings, which are now official names for the star HAT-P-6 and planet HAT-P-6b. The list of all new star and planet names can be found here.

It's nice to have such a public competition, but of course it doesn't go well. There are still countless stars, planets, comets, boulders, craters and galaxies that go through life nameless, or have to make do with just a number. How did the astronomical names originate in the past and who determines them in the future? And do stars actually need a name?

Catalogues

It used to be clear, when only a handful of planets were known in Ancient Greece and the Romans. The current planet names date from that time. Mercury, Venus, Mars, Jupiter and Saturn are names for Roman gods. The later discovered planets, Uranus and Neptune in the 18 e and 19 e century, are also named after a Greek and Roman god respectively. The name earth is a bit of an odd one and is much older, it means ground.

Only a small fraction of the thousands of visible stars have been named over the course of history. Of the names still in use today – such as Sirius, Vega or Betelgeuse – most have Greek, Latin or Arabic origins.

With the growing number of astronomers studying the heavens came the need for a systematic approach. Various naming systems emerged, such as the Bayer designation of the German astronomer Johannes Bayer. In 1603, he recorded more than 1,500 stars by combining a Greek or Latin letter with the constellation in which the star is located. The star Aldebaran is also α Tauri, which means the brightest star in the constellation Taurus.

Also by the British astronomer John Flamsteed in 1725 (after his death) a catalog was published in which a star was numbered in a similar way in combination with a constellation. There are more (and more obscure) catalogs that all co-exist. For example, the star Betelgeuse is also called α Orionis, HR 2061, BD +7 1055, HD 39801, SAO 113271 and PPM 149643.

Sprawl

Seven different names for one star is not so convenient. To make things even more unclear, a proliferation of spellings has arisen for the most famous stars with a pronounceable name. Astronomers who examined it, for example, found more than thirty different spellings for the star Fomalhaut. To rectify this, the IAU decided in 2016 to set up a special working group to create an unambiguous spelling.

Astronomer from the American University of Rochester Eric Mamajek chairs that working group and says that for the first time there is an international "policy" for the names for stars and their planets. “Over the past century, astronomers within the IAU have agreed on names of moons in our solar system, asteroids or craters on the moon. Since we continuously discover exoplanets, the need for unambiguous names has increased.”

But which name or spelling do you choose? The working group has tried to use star names from different cultures, Mamajek said. “That was not always easy. It was difficult to find literature about their astronomical traditions from many cultures,” he says. “Another point is that some cultures only name (parts of) constellations and not individual stars. There are very few cultures with many star names, and many cultures with few star names. Time and again the brightest stars were named.”

So some stars have multiple names, or vice versa, some names are used for different stars. In principle, the name most commonly used by the international astronomical community was leading. When using the same name for several stars, the working group intervened.

In 2018, the working group published a list of the official spellings for 336 stars. Mamajek announces that the working group will again work on expanding the list this year. “By the way, it doesn't mean that we ban existing alternative names, everyone is of course free to name the stars as he or she wants. We recognize alternative star names as World Heritage,” says Mamajek. “In any case, we are trying to encourage the international astronomical community to use these star names. Something similar happened a century ago with constellations.”

Smaller group

Then back to our own solar system. There are still plenty of names to share here. Planets are probably not (much) more discovered, but there are probably still enough so-called dwarf planets, especially in the outer regions of the solar system. Pluto has been the most famous member of this group since 2006.

The discoverer of a (dwarf) planet or moon may propose a name, but there are rules. For example, a dwarf planet must be named after a mythological figure or god. Naming for example after a loved one is not allowed. There the discoverer of Pluto's largest moon - Charon - got off to a good start when it turned out that he could honor his wife, Charlene, with the mythological name Charon. To the ferryman who takes the dead across the river Stix to the underworld.

Even the even smaller parts of our solar system are given names. Asteroids are chunks of ice and rock between roughly a meter and a thousand kilometers in size. There are now about 800,000 known, most of them orbiting the sun between Mars and Jupiter. The orbits of about 550 thousand asteroids are precisely known:a condition for getting an official 'number' and starting a naming procedure.

The discoverer of the asteroid receives an invitation to make a name suggestion. It has ten years to do so. The suggestion is then assessed by the IAU and possibly awarded. Of the half a million well-known asteroids, about 22 thousand have official names. This also includes a few hundred asteroids with 'Dutch' names. Most of these asteroids were discovered by Dutch astronomers Cees and Ingrid van Houten.

Finally, there are comets, which differ from asteroids in that they drag a long tail of gas behind them. The naming procedure also differs. The comet gets its name from the first two discoverers (there is a good chance that a comet will be spotted independently by multiple observers). In addition, a number and letter code is assigned corresponding to the year and month of discovery.

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Participation

For example, names are steadily being handed out, but there are still countless astronomical objects without names. On paper, the Milky Way already has enough stars to 'give' every Earth resident dozens of stars. Can we democratize naming as is the case with Starry Night and Night Watch?

Ans Hekkenberg thinks that's a good idea. She is an editor for New Scientist magazine and was a member of the jury in the recent IAU publicity campaign. “The starry sky belongs to everyone, so I think participation is a good thing,” she says. “I doubt whether such a procedure is feasible for everything we find. That will be a huge job. And a little control seems useful to me. Of the 6,100 Dutch entries for the campaign, we had to declare eighty percent invalid because they did not meet the criteria.”

Do all stars really need a name? Most are not even visible to the naked eye from Earth. “When I give a lecture somewhere, I hear people say that they find it strange that whole worlds are hidden behind those numbers. I agree that if you want to learn and convey something about a place like this, it's better that it has a real name," says Mamajek. “I believe this will come naturally. Suppose we find a planet with life, then I'm sure this place will have a name that sticks in no time.”