The tag carefully states that it is for proper IAU planets only, yet the suggested topics apply just as well to other related bodies. I suppose the same question about tectonics and composition would be tagged differently if it just happened to orbit a gas giant? And what if that's not important and not mentioned?

What about dwarf planets and rogue planets [sic]?

I think the suggestions involve the "worldness" not the orbit details, so is at odds with the first paragraph of the description and contradictory.

How can we better explain what it has been used for? I didn't just hack away at it in case someone had planned out a set of tags with some care.


I would leave as is, but with more emphasis on the "effects on system". We already have , , (for things like albedo) and we probably should have (for effects that are more generic and does not depend on body being a planet or moon). Thus, I would just remove these effects from description of , and encourage to use and where applicable, and other tags where they fit.


This may be a little difficult, since technically speaking a habitable world orbiting a gas giant would be a moon, even if you could live there.

And some bozo's decided that size makes a difference, to the shock of poor Pluto.

I don't know if "solar bodies" might be better than "IAU planet", since that might apply to planets, dwarf planets, moons, asteroids, comets, etc. While "Rogue-planets" would be outside of a solar system and so separate.

  • $\begingroup$ The nomenclature for orbital dynamics doesn't help when we care about weather or techtonics etc. That's why the tag description is contradictary. $\endgroup$ – JDługosz Jun 25 '16 at 3:46
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    $\begingroup$ @JDługosz I'm not disagreeing with you. I just wonder why the tag definition specific wording matters. If I put a planet question up and tagged it with planet, and then someone put an answer saying "well actually that's not a planet, is a dwarf moon" I'd probably down vote it because I know what I mean, and worrying about overlapping definitions is troll behavior. $\endgroup$ – AndyD273 Jun 25 '16 at 11:14
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    $\begingroup$ Well, then we could get rid of the wording and must say the tag is “about planets”. $\endgroup$ – JDługosz Jun 25 '16 at 11:36
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    $\begingroup$ If we want something that captures "anything that is in orbit of something else, except stars" then the proper term would be celestial bodies with a specific exception for stars (including pulsars and friends). I for one would have no idea what a "solar body" is supposed to be (if anything, the "solar" risks drawing peoples' attention in the opposite direction), and "celestial body in orbit around a star" is simultaneously too permissive (binary stars with large difference in mass between the two) and too restrictive (moons become a difficult edge case)... $\endgroup$ – user Aug 28 '16 at 10:00
  • $\begingroup$ @MichaelKjörling So "celestial bodies of less than 1 solar mass" then? Sounds right to me. Or we can just not worry about it, because if I tag a question with planet, and someone gets bent out of shape about a misapplied tag, then I'm not the one with the problem. $\endgroup$ – AndyD273 Aug 28 '16 at 11:42
  • $\begingroup$ Stars can be significantly smaller than 1 $M_\odot$ (solar mass). In fact, if Wikipedia is to be believed, 2MASS J0523-1403 is the lowest-mass star known, at <0.08 $M_\odot$. For comparison, Jupiter, which apparently is fairly small as far as gas giants go, is only two orders of magnitude smaller at about 0.001 (1/1047) $M_\odot$. I just feel that, if we are going to have a definition for the tag that differs from that of the scientific community, it should be thought through and appropriate. $\endgroup$ – user Aug 28 '16 at 12:01
  • $\begingroup$ @MichaelKjörling "celestial body that isn't experiencing fusion"? "Celestial body that isn't included in the definition of 'star'"? Kind of reminds me of the quote: "Science fiction is what we point to when we say it." — Damon Knight. So in this case "a planet is what I point to when I say it". The universe is big and crazy, and people keep finding things that defy the definitions that we try to impose. Whatever definition we change it to, someone will find an exception. $\endgroup$ – AndyD273 Aug 28 '16 at 12:17
  • $\begingroup$ You need to read Mike Brown's Book. en.wikipedia.org/wiki/… Brown makes a good case why the term "planet" is one of those arbitrary terms. It was either Pluto or the solar system would have hundreds or possibly thousands more planets. So they became dwarf planets. $\endgroup$ – a4android Feb 21 '17 at 12:14

This is why IAU's definition of planets is trash...

I worked out a system of nomenclature some years ago now...

Astrometric Objects:
AO 0 = possibly Black holes and other such crazy things we might find
AO I = Stellar Objects
AO II = Non-Stellar Spheroidal Objects (Shortened to Spheroidals)
AO II.a = Cryospheres
AO II.b = Terraspheres or Aquaspheres
AO II.c = Aerospheres
AO II.d = Brown dwarves (maybe)
AO III = Debris, Comets, Asteroids
AO IV = Maybe ships if ever needed ^.^

An AO II that orbits a AO I = Planet
An AO II that orbits another AO II = Moon

AOIs are objects that are Luminous and all the normal stuff that defines stars which I can't remember off the top of my head.

AOIIs are defined basically as any object that has a large enough mass to shape it into a sphere. The different sub-groups are have relationships to masses, but just looking at them you can tell what they refer. Small Frozen bodies, Medium Earthlike worlds, Large Gas Giants.

Defining like this removes the idiocy that is tha IAU standard where bodies can be Planets for a time, but then get ejected from a Sytem to become not planets and then be caught in another star system to become a planet again... but only if its orbit has already been cleared out... v.v This definition makes it clear what you're talking about and places Planet and Moon as more layman labels than real categorization as they should be regarded.

Of course the problem with referring to things like this is that it's not the standard nomenclature so noone will ever know that this is how you refer to them.

  • $\begingroup$ What is «v.v» ? $\endgroup$ – JDługosz Jan 21 '17 at 4:25
  • $\begingroup$ @JDługosz It's an emoticon...an old one too. ^.^ generally means positively speaking or sarcasm while v.v generally means negatively speaking often to signify condecension or indicating the idiocy of the thing that it pre or procedes. in this case it is emphasizing how stupid the "but only if its orbit has been cleared out" line, although I probably should have put it before the ellipses which I use because they're more accurate to my train of thought. That is, there isn't a pause or period, but a continuation of thought that is being left out, though it is where most people would use commas. $\endgroup$ – Durakken Jan 21 '17 at 4:56
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    $\begingroup$ I was the downvoter here. The IAU system may not be perfect, but at least people know how to use it. $\endgroup$ – HDE 226868 Jan 21 '17 at 18:58
  • $\begingroup$ What @HDE226868 said. We have discussed site-specific nomenclatures before, and they repeatedly get shot down for the same reason: We want to be inclusive, not exclusive, to newcomers. Specific technical terms have merit, but only when everyone who has reason to use them can be fully expected to know their meaning. $\endgroup$ – user Feb 20 '17 at 9:53
  • $\begingroup$ @MichaelKjörling I'm not saying to adopt this, just putting it in another area so that maybe someone who can make a difference sees it and proposes it to fix it, but to your argument, it's not sound as it relies on the idea that people know what the IAU system is and that it makes sense. They don't and it doesn't so it doesn't really make a difference. You're always going to have this problem until the IAU changes their standard or you use the coloquial definition that everyone uses. $\endgroup$ – Durakken Feb 20 '17 at 10:23
  • $\begingroup$ Your scheme doesn't appear to include dwarf planets, but I may be misreading it. It's worth reading Mike Brown's book. It helps understand the issues of planetary classification. en.wikipedia.org/wiki/… $\endgroup$ – a4android Feb 21 '17 at 12:21
  • $\begingroup$ @a4android It does, they fit into spheroidals (cryospheres), if they're not then they go into Debris. The reason for the spheroidal's be broken down into 3 sub categories is because planets at certain sizes tend to have pretty much the same basic attributes. There are very few examples that we have that doesn't quite fit, like Mercury which is basically because Mercury was closser to a Terrasphere and then had most of itbody blown off apparently... $\endgroup$ – Durakken Feb 21 '17 at 14:08
  • $\begingroup$ Thanks for the clarification. Fitting things into categories is always difficult. This one aspect Brown's book covers well. There will always something that can only be dealt in an arbitrary manner. $\endgroup$ – a4android Feb 22 '17 at 5:17

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