Space is a big place, with a lot of galaxies, stars, planets and moons, and that means a lot of names. How do astronomers name stuff, like comets, asteroids, exoplanets, craters?

Download MP3 | Show Notes | Transcript

Show Notes

Thanksgiving Day in Canada (Timeanddate)

How did all the planets with their moons get their names? (Astronomy Magazine)

Ancient African Skies (

PAPER: Origins of the ancient constellations: I. The Mesopotamian traditions (Journal of the British Astronomical Association)

Whose stars? Our heritage of Arabian astronomy (The Planetary Society)

Division C WG Star Names (IAU)

Maori Astronomy (New Zealand Astronomy)


The moons of Jupiter (Universe Today via

The Shakespearean Moons of Uranus (Folger Shakespeare Library)

List of geological features on Europa – Chaos Terrain (Wikipedia)

6 Mars craters that are named after PH towns (Manila Bulletin)

International Astronomical Union

United Nations

Mike Brown (Caltech)

Pluto and the Solar System (IAU)

Naming of Astronomical Objects (IAU)

Naming of Astronomical Objects – Comets (IAU)

Pan-STARRS1 data archive (Space Telescope Science Institute)

Asteroid numbers and names (ESA)

Asteroid (158092) Frasercain (RASC)

Announcing Asteroid 158092 Frasercain (Universe Today)

How do exoplanets get their names? (NASA)

The Interactive NGC Catalog Online (SEDS)

Smithsonian Astrophysical Observatory Star Catalog (SAO)

The Abell catalog of planetary nebulae (In The Sky)

Back to Top


Transcriptions provided by GMR Transcription Services

Fraser:                         Astronomy Cast episode 657: astronomy naming schemes. Welcome to astronomy cast, our weekly facts-based journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, the publisher of Universe Today.

                                    I’ve been a space and astronomy journalist for over 20 years, and with me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey Pamela, how you doing?

Pamela:                        I am doing well. How are you doing?

Fraser:                         Good. Happy Thanksgiving.

Pamela:                        Happy Canadian Thanksgiving.

Fraser:                         Yeah. Every year, we record on a Canadian Thanksgiving because we record on Mondays and it’s always on Mondays, and I always lord over you how much superior Canadian Thanksgiving is to US Thanksgiving for one reason.

Pamela:                        Go ahead.

Fraser:                         Weather. That.

Pamela:                        It’s true.

Fraser:                         We hold our Thanksgiving a month earlier –

Pamela:                        Yes.

Fraser:                         – and that means that the weather is going to be better. And so, if people are flying, it is less mayhem –just because you’re just gonna have milder weather. And so, people can make the journey without it just being horrible snowstorms and such. And once again, we’re having a draught here in western Canada, so if anybody wanted to fly, it’d be easy flying to get out here to western Canada.

                                    But yeah. So, happy Thanksgiving. I guess we’ll take off US Thanksgiving, but we’ll work through Canadian Thanksgiving.

Pamela:                        But I still think they’re gonna launch SLS on American Thanksgiving, which means we will be working.

Fraser:                         Right.

Pamela:                        At least, I’ll be working.

Fraser:                         Right, of course. They absolutely will be launching SLS on some kinda holiday.

                                    Space is a big place with lots of galaxies, stars, planets, moons, and that means a lot of names. So, how do astronomers name stuff? Like comets, asteroids, exoplanets, craters? All right, everything’s got a name. So, I guess let’s start with the easy stuff – the stuff that we’ve known the names of for antiquity. Where do we get those names from?

Pamela:                        So, do you mean things like planets?

Fraser:                         Yeah, the planets, bright stars –the moon –the sun – Right? These things have names. Where did they come from?

Pamela:                        So, the original names for the planets that we use in the English language – they simply come basically from the Greek and Roman names for them. And so, we have – Saturn is a Roman god, we have – Jupiter is a Roman god, but these are the Romanized versions of the Greek gods’ names. So, we basically just fell back on the names the Romans stole and changed and kept them for ourselves.

Fraser:                         But what about names like “the moon” or “the sun”?

Pamela:                        Well –

Fraser:                         “The earth.”

Pamela:                        Yeah. That is, again, just ancient language where I am not the kind of anthropologist that can explain these truly ancient words that –

Fraser:                         Right.

Pamela:                        Yeah. I mean, earth is the dirt under our feet. The fact that it’s a planet that we stand upon – that one took a hot minute to figure out.

Fraser:                         But I think it’s funny, right? I get emails all the time from people saying like, “What is the name of the moon?” and I say, “It’s the moon.” And then, someone will comment like, “No, no, no; it’s Luna.” But that’s not true. That’s just another language –

Pamela:                        That’s just the name in another language.

Fraser:                         In another language.

Pamela:                        Yeah.

Fraser:                         Yeah. Yeah, the sun – you know, “Soleil” – whatever you wanna call it – earth, “Terra” – just another –word in – and the reason is because we didn’t know there were others.

Pamela:                        Right.

Fraser:                         And so, it’s just like, of course it’s “the moon” – it’s a name for the thing that’s in the sky. You don’t realize that it’s actually a classification of objects. Antiquity, they just thought it was the thing.

Pamela:                        Yeah.

Fraser:                         So –yeah, I find that really funny.

Pamela:                        Well, and what gets really amazing is when we start looking at stars, there are some stars whose names linguists think are so old that they go back to like –pre-distribution-of-humans-all-over-the-planets times.

Fraser:                         Wow.

Pamela:                        And –

Fraser:                         That’s really interesting.

Pamela:                        – the idea that there are stellar names that go back prior to –homo sapiens’ diaspora from Africa – Like, that’s a phrase I never thought I would be saying, but the stars have just been an integral part of our lives for that long.

Fraser:                         But there are – I mean, in the west, a lot of our names come from Arabic astronomers –

Pamela:                        Yes.

Fraser:                         –as well as like Sumerian and – Again, just cultures that are thousands of years old in some cases, we still use those names. And in some cases, just lost to antiquity. And then, every society – I mean, people in China have names for the different stars that they have, again, from antiquity. And probably –you know, I’m sure the Aztecs had their names for everything as well.

Pamela:                        And luckily, there were only a few thousands of naked-eye stars for astronomers, or astrologers, or whatever they were in whatever culture – magi – there were only 1,500 to 2,000 stars that could be seen and catalogued by the naked eye, and not all of those had common names.

                                    So, we have a few stars like Betelgeuse, Sirius that have these names that are words –and everything else luckily just got catalogued.

Fraser:                         I wish we could kinda go back and look at the names that every culture has given the same star and then be able to present them as like a menu and go like, “I like this one the best.” I’m sure there are some really cool names that the aboriginals in Australia came up with for stars and things like that. It’d be great to sort of have the whole list. Wonder if anyone’s built a cross-cultural list.

Pamela:                        Yes. Yes. I’m like exploding with vibrations here waiting to say yes. The International –

Fraser:                         Anyway, I guess we’ll never know. Go ahead.

Pamela:                        So, the International Astronomical Union has a committee on stellar names that is working to collect the names from various cultures around the world so that we don’t lose these names, and in places like New Zealand where they’re working so hard to commemorate the people whose land that they stay on who are still alive and still there, you can actually go to museums and by star charts that have the Maori peoples’ names for stuff. They are working to keep this information that could so easily have been lost, and software like Stellarium will even let you turn on and off the constellations of different cultures.

Fraser:                         Oh, that’s cool. Okay. Yeah, I mean, there’s gonna be some badass names for some of the objects in the sky, and I think we should be able to settle in on a cross-cultural collection that is only the coolest names.

Pamela:                        Yes.

Fraser:                         Anyway, so, then, objects that have been discovered in modern times –

Pamela:                        Yes.

Fraser:                         I’m thinking about the extra planets, the moons, and etcetera. How does that naming scheme work?

Pamela:                        Well, those are a couple of very different time periods that these rules ended up coming from, so what we have – for Jupiter – initially, Jupiter – it was the wives of Jupiter, and mistresses as well that the names were drawn from. So, Jupiter is literally being circled by mistresses, which just amuses me to no end, but as they got further and further down, they did eventually run out of mistress’s names to use.

                                    So, these are all names that are drawn from mythology. With Saturn, you have Shakespearian names kick in at a certain point. And so, each world has its own slightly different sets of rules, and with worlds that have surfaces that we can define features on, it gets kinda crazy.

                                    So, for Europa, you have the chaos terrain that is named after Celtic myths. You have craters that are named after Celtic gods and heroes – ring features are named after Celtic stone circles. So, you see how astronomers latch on a theme and go down the rabbit hole.

Fraser:                         Right. The mythology rabbit hole –features very strongly across the naming schemes for the solar system.

Pamela:                        And sometimes, it’s not just mythology. With Mars, one of my favorite details is small craters are named after places on earth with a population less than 100,000.

Fraser:                         Hm. I wonder if there’s a Courtney crater out there, then.

Pamela:                        There could be. Or, you could go name one. Or, propose to the IAU the name of one.

Fraser:                         I guess so. Yeah. Yeah. All right, we’re gonna talk about this some more, but it’s time for a break.

Fraser:                         Now, you’ve said this is the name for that, and those are the names for these, and they’re getting the official names, so who decides what the names are?

Pamela:                        There are a variety of different committees within the International Astronomical Union, which is a global union of scientists that works in collaboration with the United Nations, actually, in a lot of different things.

                                    And there’s the Planetary Naming Conventions Group, there’s the Asteroid or Minor Planet Naming Conventions Group, there’s the Stars Naming Group, and the fact that these are all separate committees under different –parts of the IAU sort of –came to a nasty head in 2006 because –Michael Brown had discovered a new large object out in the Kuiper belt that was potentially larger than Pluto, and the question was “Does it get to be named by the IC Objects Minor Planet Naming Committee, or does it get to be named by the Planetary Naming Committee?”

Fraser:                         Whoa.

Pamela:                        And –

Fraser:                         You’re talking about Eris here?

Pamela:                        Yeah.

Fraser:                         Yeah.

Pamela:                        And it comes down to –they had to have a definition of what a planet is so they knew which committee got to approve the name.

Fraser:                         That’s crazy! Is that real? Is that –?

Pamela:                        Lovely. It’s real.

Fraser:                         So, the reason why whether or not Pluto is a planet had to come to a vote was because they needed to decide who got to name Eris?

Pamela:                        Well, it’s slightly more complex. It was the –

Fraser:                         No, no, no. It feels as simple as that.

Pamela:                        It was the realization that we don’t have a definition of what makes a planet, and both groups wanted –dominance over these objects.

Fraser:                         Yeah. Right. And so, they forced a vote.

Pamela:                        And so, basically – Yeah, they forced a vote. And they came up with a terrible definition.

Fraser:                         Why did you never tell me this before?

Pamela:                        I’m sure I did at some point!

Fraser:                         No. No, no, no, no, no. No, we talked…

Pamela:                        I failed. I failed you.

Fraser:                         It’s not that you failed, but it’s just like, you buried the lead. Like, this is the chain of events: Mike Brown finds an object. The object is Pluto-sized – therefore, theoretically, it’s planet-sized.

Pamela:                        Yeah.

Fraser:                         Who gets to name it? The two groups – because it falls somewhere between those two groups, they had to decide whether it was a planet or not, and if it’s a planet or not, then Pluto’s a planet or not, and –

Pamela:                        Right.

Fraser:                         Wow. Anyway –

Pamela:                        Isn’t that –delicious?

Fraser:                         Yeah. Yeah. Yes. Yeah. I’m sure there are certain members of the “I love Pluto” community that are just raging right now –

Pamela:                        I refer to it as “Pluto: Planet Classic.”

Fraser:                         Yeah. Me, as having absolutely no dog in this fight, don’t care at all. My emotion neither rises nor falls with any mention of Pluto’s pro- or non-planethood.

Pamela:                        I’m just amused.

Fraser:                         But I do find it funny that this is the story.

Pamela:                        Yes.

Fraser:                         So, I mean – but the names – like Makemake, Eris – Those were suggested by Brown – by Mike Brown.

Pamela:                        So, the way it works is the people who find the objects get to propose names, but they don’t get to –say outright “These are the names.” They have to propose the names, fill out paperwork, submit the paperwork, the committee has to meet, the committee has to approve, and thus, you get a world that has been named.

Fraser:                         All right. All right, let’s move on, then. Let’s talk about comets. How do comets get their name?

Pamela:                        So, comets are fairly straightforward. They get the name of the humans that found them, the year that they were discovered, and depending on which nomenclature you’re looking at, you may see additional letters and numbers that have to do with “Are they periodic or non-periodic comments?”

                                    One of the problems we run into is comet nomenclature as well as minor-planet-naming nomenclature got revised. And so, if you’re looking at something from like the 1980s or if you’re looking at something from the 2000s, you’re gonna see different ways of stating the nomenclature.

Fraser:                         So, take any example comet, and break it down for me.

Pamela:                        Comet Halley – named strictly after Halley.

Fraser:                         Right. But Comet Halley, for example, is a bad example because Halley didn’t find it – it had been known for 100’s of years, and it had been coming back again and again. So, I think that’s a bad example. Like, it shoulda been Comet “That Comet We’ve All Seen for a Long Time and Talked about, and No One Ever Really Put a Name to It.”

Pamela:                        So, the thing is we didn’t know what comets were before Halley put –one in many together and got an orbit.

Fraser:                         Right.

Pamela:                        Halley looked through history and found that every 70-something years, this bright-tailed object streaked through the sky –

Fraser:                         But that’s just accounting. That’s not like noticing a comet for the first – I’m saying – Halley should lose his naming rights for the comet. It should be stripped.

Pamela:                        But we don’t know who the first pre-diaspora human to notice the comet was.

Fraser:                         That’s the historians’ problem. It’s not my problem. Not my problem.

Pamela:                        I’m just gonna keep saying “diaspora” today.

Fraser:                         Yeah. Yeah. So, that is a historian’s problem. I’m just saying that Halley getting the comet named after him is illegitimate and should be stripped. But I’ll let the IAU have that fight. I’m ready. I’m ready to present my case.

                                    But a modern comet, like Hyakutake or Hale-Bopp. Now, those are brand new comets that nobody’s ever seen before.

Pamela:                        Right. Those are, again, from some of the earlier nomenclature where they’re named after the discoverer. It gets more chaotic with modern comets, but since PAN-STARRS is finding most of them, we are glad for the chaos.

Fraser:                         Right.

Pamela:                        So, for instance, there is Comet/2017 K2 (PAN-STARRS).

Fraser:                         Perfect. Okay. So, that’s a jumble of information. What does that mean?

Pamela:                        Yes. So, that means it was found in 2017. The K2 starts to give you information on the where in a given month and which number in a given month it is that it was found, and PAN-STARRS is the discoverer. So, in this case, it’s just a telescope survey.

Fraser:                         It’s a robot.

Pamela:                        Yeah. Yeah, it’s kinda boring.

Fraser:                         Right. Beep-boop. Right. So, robots. So, would you say that accurately, the comets are named after robots?

Pamela:                        Yes. And I am okay with this.

Fraser:                         Yeah, I’m all right with that. That’s fine. I mean, this really should smooth over the rise of the robots. Like, when they come to dismantle us for our atomic parts, we’ll say, “But, well, we named all these comets after you,” and they’d be like, “You humans. Aw, shucks. All right. No matrix for you. No termination. We’ll live in peace and harmony until the end of time.”

Pamela:                        I don’t think it’s gonna work that simply, but I hope you are right.

Fraser:                         It’s worth a shot. It’s worth a shot.

Pamela:                        It’s worth a shot.

Fraser:                         Yeah. All right. So, now, for the best part. We’ve talked about comets. Let’s talk about asteroids. How do asteroids get their name?

Pamela:                        My dog just sighed as well.

Fraser:                         Good.

Pamela:                        So, asteroids get their name basically in the order they have been found. So, it’s asteroid one, two, three, four, and then, sometimes –if they’re a lucky asteroid –someone decides to grant them a name.

Fraser:                         Yeah.

Pamela:                        And again, the name has to be approved of by an International Astronomical Union committee, but in the past, we didn’t have this committee. So, you can go and look up the earliest discovered asteroids, and they have the number, and the name, and the IAU was not involved – Ceres, Vesta – they were just names.

Fraser:                         But that’s interesting. So, when you see 4 Vesta, or 1 Ceres, or whatever – when you see the number, you know that it is –

Pamela:                        What order it was found in.

Fraser:                         What order it was found in. And so, for example, Asteroid, I don’t know – 158,092 – That was –

Pamela:                        We haven’t got that high yet, but continue.

Fraser:                         Yes we have. We absolutely have.

Pamela:                        We have? Oh, geez.

Fraser:                         Yeah. Yeah, asteroid 158,092 – Asteroid Frasercain – was the 158,092nd asteroid that was discovered.

Pamela:                        All right. All right. Fair. Fair enough.

Fraser:                         So, yeah. How did it get the Fraser Cain part of its name?

Pamela:                        So, either the person who discovered it –or, if it got ignored long enough, someone who noticed that it had been ignored long enough submitted to the IAU that this asteroid deserves a name. And this name I am proposing commemorates someone who is good and noble, and had done excellent things, and has a name that is absolutely not controversial.

Fraser:                         Right. And so, in this case, Jeff Metcalf – the blue-collar scientist who passed away –

Pamela:                        In 2008.

Fraser:                         15 years ago? Yeah.

Pamela:                        Yeah.

Fraser:                         –was a prolific asteroid discoverer and named asteroids after a whole bunch of people in the science and science communication community.

Pamela:                        Yeah. Yeah, You and Phil Plait got your names at the same time.


Fraser:                         Got me, got Phil, Emily Lakdawalla, but missed you, and we’re always sorry. So, if anyone’s listening to this and you discover asteroids, throw a bone to Pamela. Come on. She could really use an asteroid named after her.

Pamela:                        Well –yeah.

Fraser:                         So, the point being: Jeff discovered the asteroid, got to provide the name, and it was – Like, it’s not that he got to suggest the name to the community. It was more like if he had said something trolling or hateful, then they could’ve stripped it, but that was gonna be the name because I guess there are so many asteroids being discovered all the time.

Pamela:                        Yeah.

Fraser:                         Yeah. That’s really cool. Now, what about exoplanets?

Pamela:                        So, exoplanets – we haven’t started giving them other than occasionally, a research team will bestow a name upon something they find, but those I don’t believe are considered official anywhere.

                                    They get names that are lowercase A, B, C, D, E according to their distance or their discovery order from their main star. So, if we end up finding something later that is closer in then things get to be a jumbled mess, luckily, it’s usually easiest to find the thing that’s innermost. So –

Fraser:                         But there is no “A”. The A is the star –right?

Pamela:                        Right.

Fraser:                         Right. So, say you have Pegasi 51 – the first planet every discovered…

Pamela:                        Actually, I’m gonna factcheck that one because this is a lowercase and there’s [inaudible] [00:26:41]

Fraser:                         Okay. Because my understanding – like, you’ve got 51 Peg B, and that was really the first planet orbiting a sunlike star that was ever found – in 1995 – and that’s the B. And so, the first one found is the letter, but if you find a bunch at the same time, then, they typically will to them from the inside out.

                                    But the category – like, the actual name – like Gliza, the Trappist – Kepler – like, those are coming from the telescope. So, essentially, the telescope is the first part of the name – Gliza –whatever. The star catalogue. Then, it is the designation in the catalogue – so, 5,781-whatever, and then, it is the letter designation, which is the planet, and whether it’s closest to the star or first discovered –

                                    Because –there are probably more planets in, say, the 51 Peg system than the one that we know of – the hot Jupiter that we know of – but they’re just too feint to see. And so, do you shift everything if you find more? No. You just – you find a closer one; now it’s C. And then, [inaudible] [00:28:09] D, and then, the one in between those two – that’ll be E.

                                    So, it’s really in the order that they’re found. But if you’re gonna find a bunch at the time –

Pamela:                        Yes.

Fraser:                         –then you just – like the Trappist planets – then you put them all in a row nicely.

Pamela:                        You are entirely correct, and the reason I had to take a moment to be confused is multi-star systems. So –

Fraser:                         Right. It’s capital though, right?

Pamela:                        Yeah. And this is where the capital versus the lowercase comes into play. So, back in my Slacker Astronomy days, we took great delight in the discovery of a planet in the Tau Boötis system orbiting the primary star, which is A. So, it is legitimate to either say “Tau Boötis, capital ‘A,’ lowercase ‘b’,” or to simply say “Tau Boötis B,” but you really always just abbreviate it. So, it’s Tau Boö B, and I’m apparently an eight-year-old and still take delight in that.

                                    So, if it’s the primary star of a binary system, you can omit the letter. If it’s a secondary, tertiary, whatever star in a multi-star system, it would be the star designator – so, that’s usually a number – and then, for bright stars. So, Bayesian number, the constellation name, the capital letter of the star and the multi-star system when the letter is not A –followed by the lowercase letter.

Fraser:                         Right. And then, you’re also gonna see the names of stars, galaxies, pulsars – things like that, and it’s gonna be a jumble of numbers and letters. That just comes from some star catalogue.

Pamela:                        But they have a meaning. Those have meaning.

Fraser:                         Sure. Two mass – Yes. The HD – Yeah, they do have meaning. They’re named after the catalogue that they’re stored in.

Pamela:                        But the license plate that follows the catalogue actually has meaning.

Fraser:                         Right.

Pamela:                        So, the NGC numbers don’t so much have meaning. Those are just kind of the order they got listed and more discovered, and those go all the way back to like –when Herschel – all three of them were cataloguing things. So, William Herschel, his younger sister Caroline Herschel, his son John Herschel – they all helped contribute to the new general catalogue. That’s how old the new general catalogue is.

Fraser:                         Right.

Pamela:                        But modern catalogues – so, for instance, if you’re looking at a Abell galaxy cluster, you have the Abell number, which is the order in which it was found, and if there’s an S in front of it, that means it’s a southern hemisphere system –ID. So, it’s Abell – no letter means northern hemisphere; S in front of it means southern hemisphere –

                                    But Abell, for instance, SO295 is also catalogued as XRCJ0245.45302 –

Fraser:                         Right.

Pamela:                        And that means that it is the object that was found in the Chandra mapping of the region that has that particular Julian date – so, J2000, a coordinate describing where it is. And they usually only give the RA part of that license plate, but if you go to the actual catalogue, it will then have either a plus or a minus and give you the [inaudible] [00:31:56] as well.

Fraser:                         And so, you can see the name of the object and know where to find it in the sky. As opposed to having to look up a catalogue, find the location of the object, you can just find it there in the name. But what if they drift overtime? That’s a terrible naming scheme.

Pamela:                        No, no, no. So, the reason that they have that J in front or they have a B – which means the 1950’s coordinate system – that letter that you have in front tells you when that position is good for. And so, we know when it has a J in front of it, those coordinates are completely right for 2000 on the specific date that the calendar is set to zero on. And it’s the same for the 1950.

Fraser:                         Yeah, you can just modify based on the clock. All right. We could do this all day. The point being: if you see a great big jumble of letters and numbers after some object, that is the astronomers attempting to communicate important information about the object’s location right there in the name, which is smart, but also incomprehensible for the rest of us attempting to read it.

Pamela:                        True.

Fraser:                         All right. Thank you, Pamela.

Pamela:                        Thank you, Fraser. And thank you to everyone out there who helped support this show this week.

                                    I would like to thank Alexis, William Baker, WandererM101, Zero Chill, Felix Gutt, Astrosetz, William Andrews, Gold, Roland Warmerdam, Jeff Collins, Simon Parton, Kellianne and David Parker, Jeremy Kerwin, Stuart Mills, Rob Cuffe, Harald Bardenhagen, Phillip Walker, Daniel Loosli, Matthew Horstman, Alex Cohen, marco iarossi, David Gates, Scott Bieber, Rando, Disasterina, Scott Kohn, Kseniya Panfilenko, Jim Schooler, and Justin Proctor. Thank you all so much for all you to do help support our show. Thank you.

Fraser:                         And we’ll see you all next week.

Pamela:                        Bye-bye, everyone.

                                    Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons attribution license. So, love it, share it, and remix it, but please, credit it to our hosts, Fraser Cain and Dr. Pamela Gay.

                                    You can get more information on today’s show topic on our website, This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at Cast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events.

                                    We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.


Submit a Comment

Your email address will not be published. Required fields are marked *