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Tags astronomy , pluto

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Old 11th September 2018, 05:13 AM   #81
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Originally Posted by angrysoba View Post
I don’t get what “relevance” has to do with it. This surely depends on what we consider relevant at any one time.
It's a value judgment.
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Old 11th September 2018, 05:16 AM   #82
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Originally Posted by Ziggurat View Post
At a certain point, this stuff should be obvious. A dwarf planet should be something too small to be a real planet. A definition of dwarf planet that includes Jupiter is a bad definition, because it's misleading.
Again, I'd ask what you base your "should" upon.

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No, it isn't. An egg shell is not an egg.
Good. Do we agree that a planet that loses its planet...ary qualities is no longer a planet, regardless of what those qualities are?

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Sure, but you've offered neither objection nor alternative.
Because I'm still trying to grasp what your alternative is, and why it's more useful. So far, as I noted, mostly your reasoning is that it "feels" right to you. I don't find that very convincing.

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No, it's not a problem of classification. It's not a problem at all.
Ok why do we classify genera and species and orders at all, then? It's because there's a crapton of lifeforms and we want to be able to classify them for various purposes. It's the same with solar system bodies.

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And why does your personal preference matter?
It no more matters than yours, actually. I didn't claim otherwise.

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Furthermore, I've already suggested multiple better ways to eliminate those smaller objects from the definition.
No, they all orbit the sun and have hydrostatic equilibrium.
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Old 11th September 2018, 05:32 AM   #83
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Originally Posted by Belz... View Post
Again, I'd ask what you base your "should" upon.
I just told you in the very part you quoted: because it's misleading. Really, Belz, do pay attention.

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No, they all orbit the sun and have hydrostatic equilibrium.
You forgot that I already suggested using a mass or diameter threshold if you want to eliminate smaller objects.
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Old 11th September 2018, 05:47 AM   #84
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Originally Posted by Ziggurat View Post
I just told you in the very part you quoted: because it's misleading.
I read it. Your jab about Jupiter is irrelevant to the larger point, and 'misleading' is meaningless in this context, since we're discussing defining the term 'planet' in the first place. I'm asking you why you're putting "should" in your arguments over and over. You're not going go make your case if you keep phrasing your arguments in moral language. How do you determine what "should" or "shouldn't" be used? We're talking about planets, not gay marriage.

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You forgot that I already suggested using a mass or diameter threshold if you want to eliminate smaller objects.
I didn't. Stop trying to make it about me. What mass would you suggest, and why? How would that be useful in any way?
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Old 11th September 2018, 06:11 AM   #85
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Originally Posted by Belz... View Post
I read it. Your jab about Jupiter is irrelevant to the larger point
It's completely relevant to whether or not the IAU definition is a good definition to use.

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and 'misleading' is meaningless in this context, since we're discussing defining the term 'planet' in the first place.
It's completely meaningful. A definition of the word which leads to misleading usage is inferior to a definition of the word which does not lead to misleading usage.

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I'm asking you why you're putting "should" in your arguments over and over. You're not going go make your case if you keep phrasing your arguments in moral language. How do you determine what "should" or "shouldn't" be used? We're talking about planets, not gay marriage.
"Should" implies a value assignment, but that doesn't require that the value is a moral one. And a value assignment is necessary here. If there is no value assignment, there can be no preference, and everything is arbitrary. The entire premise of even discussing what definition to use is that we can assign some value to different definitions to compare them.

I thought your complaint was just that my explanation for the value assignment wasn't clear to you, but if you're objecting to having a value assignment at all, then there's really no point in even having a discussion.

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I didn't. Stop trying to make it about me. What mass would you suggest, and why? How would that be useful in any way?
You were the one who claimed it would be useful to eliminate those smaller, less relevant objects from the definition of planet, not me. And a threshold for mass or diameter is better than clearing the neighborhood to achieve that goal because it's less ambiguous, easier to evaluate, and doesn't produce misleading usage.
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Old 11th September 2018, 06:24 AM   #86
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Originally Posted by Ziggurat View Post
It's completely relevant to whether or not the IAU definition is a good definition to use.
Only if I accept your value judgment, which you have to admit is not something you can establish convincingly.

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It's completely meaningful. A definition of the word which leads to misleading usage is inferior to a definition of the word which does not lead to misleading usage.
Except how is it misleading?

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"Should" implies a value assignment, but that doesn't require that the value is a moral one. And a value assignment is necessary here. If there is no value assignment, there can be no preference, and everything is arbitrary.
It's a definition. Of course it's arbitrary. I just don't think you've established why anything "should" be this way or not.

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I thought your complaint was just that my explanation for the value assignment wasn't clear to you, but if you're objecting to having a value assignment at all, then there's really no point in even having a discussion.
Well, let me clarify: I don't think the value judgment in and of itself is undesirable. But if you want to convince people that your judgment is correct, you'll have to do more than just state it.

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You were the one who claimed it would be useful to eliminate those smaller, less relevant objects from the definition of planet, not me.
So what mass would you choose?
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Old 11th September 2018, 06:25 AM   #87
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The 'clearing its orbit' thing is pretty nonsensical, IMO. The Trojans share Jupiter's orbit precisely because Jupiter is very massive and able to herd asteroids into its Lagrange points. Earth also has a trojan at its L4 point and several other bodies locked into a 1:1 resonance orbit, including Cruithne.

The other definitions seem fine to me - enough gravity to pull itself into approximately spheroid shape and in orbit around the sun (star, stars) rather than another planet.

Other star systems may have twin planets orbiting each other, where their sizes are so similar that it makes no sense to name one of them as a planet and the other as a moon - but that does not apply in the solar system to any planets/moons/dwarf planets so far discovered.

You could introduce other arbitrary definitions, such as "visible to the naked human eye." That might include Uranus, even though the ancients never noticed it, but would exclude Neptune, Pluto and other dwarf planets.

As someone said already, whenever you attempt to classify things, there are always likely to be edge conditions. Introducing ill-defined criteria such as 'sweeping clean their orbits' just leads to confusion and argument.

If you want to exclude Pluto, just set a minimum mass to qualify as a planet - that would mean you could then leave out the 'pulling itself into a sphere' requirement as any potential planets bigger than Pluto but smaller than Mercury would do that anyway.
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Old 11th September 2018, 06:26 AM   #88
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Originally Posted by Roboramma View Post
I say we go back to seven planets: the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn.
Neptune called and said to stick your suggestion up Uranus!
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Old 11th September 2018, 06:27 AM   #89
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Originally Posted by JoeMorgue View Post
The Solar System:
Age: 4.568 billion years.
Address: Orion-Cygnus arm of the Milky Way Galaxy.

- 1 G-Type Main Sequence white/yellow dwarf Star
- 4 Rocky, terrestrial planets.
- 4 Gas Giants
- 5 Dwarf Planets (5 named, multiple likely further candidates)
- Unknown quantity (at least 778,897) of Minor Planets
- 525 natural satellites (185 planetary, 347 minor planetary)
- Asteroid Belt, Kuiper Belt, Oort Cloud, may various trans-Neptuian objects.
- At least 4,017 comets
- 1 Teapot (Status contested)
you forgot 1 Tesla Volt.....
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Old 11th September 2018, 06:45 AM   #90
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Originally Posted by Belz... View Post
Well, let me clarify: I don't think the value judgment in and of itself is undesirable. But if you want to convince people that your judgment is correct, you'll have to do more than just state it.
I don't think most people need a lot of convincing that things like clarity are good values to have in language.

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So what mass would you choose?
You're the one who wants to filter out smaller objects, not me. I'm just suggesting a better way to do it than clearing the neighborhood. Pick whatever mass threshold filters out a number you find optimal. I'm perfectly content to not bother at all.
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Old 11th September 2018, 07:50 AM   #91
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So is your problem with the definition, or the fact, that Pluto specifically is not a planet anymore ?
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Old 11th September 2018, 08:31 AM   #92
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Originally Posted by Dr.Sid View Post
So is your problem with the definition, or the fact, that Pluto specifically is not a planet anymore ?
Primarily the definition, which I think is a clumsy kludge to exclude Pluto for arbitrary reasons while trying to mask that its exclusion is arbitrary. If you're going to exclude Pluto arbitrarily, at least make the dividing line clean, like mass or diameter.

I admit that I would like a definition that includes Pluto as well, but I've actually got more love for Haumea than Pluto. Haumea is really cool, and I'd like to see it as full fledged planet.
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Old 11th September 2018, 08:37 AM   #93
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Originally Posted by Ziggurat View Post
I don't think most people need a lot of convincing that things like clarity are good values to have in language.
You're the one making the CLAIM that it would be clearer and less misleading and all that. I'm asking you to make a case for it. Otherwise this discussion is simply you having an opinion you can't support and me having an opinion, and everybody has an opinion but no argument.

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You're the one who wants to filter out smaller objects, not me.
Yes but you proposed mass before that point, hence my question.
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Old 11th September 2018, 08:38 AM   #94
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Originally Posted by Ziggurat View Post
Primarily the definition, which I think is a clumsy kludge to exclude Pluto for arbitrary reasons while trying to mask that its exclusion is arbitrary.
The original idea was to manage the growing number of trans-neptunian bodies that were being discovered. I don't think they set out to exclude Pluto specifically, but I could be wrong.
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Old 11th September 2018, 08:39 AM   #95
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Originally Posted by Ziggurat View Post
Primarily the definition, which I think is a clumsy kludge to exclude Pluto for arbitrary reasons while trying to mask that its exclusion is arbitrary. If you're going to exclude Pluto arbitrarily, at least make the dividing line clean, like mass or diameter.

I admit that I would like a definition that includes Pluto as well, but I've actually got more love for Haumea than Pluto. Haumea is really cool, and I'd like to see it as full fledged planet.
Now this sounds as though you are attributing dark motives to those who excluded Pluto, but I think the argument does not stand up.

I recently heard a podcast between Sean Carroll and Michael Brown. The latter wrote a book called How I Killed Pluto and Why It Had It Coming. On the podcast, and presumably in greater length in the book, Michael Brown explained that he had been one of the people most responsible for arguing against planethood for Pluto, but also that he would have had most to gain from including Pluto, and indeed Haumea, and Eris, and Makemake given that he had discovered them!
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Old 11th September 2018, 09:10 AM   #96
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Originally Posted by Belz... View Post
You're the one making the CLAIM that it would be clearer and less misleading and all that. I'm asking you to make a case for it.
I already did. At some point, repetition becomes pointless.
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Old 11th September 2018, 09:12 AM   #97
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Originally Posted by angrysoba View Post
Now this sounds as though you are attributing dark motives to those who excluded Pluto, but I think the argument does not stand up.
No, I don't mean dark motives. I mean I think they decided to exclude Pluto, for reasons which don't really matter to me here, and then found a definition which would do that, rather than develop a definition and then see if Pluto would fit it.
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Old 11th September 2018, 09:14 AM   #98
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Originally Posted by Belz... View Post
The original idea was to manage the growing number of trans-neptunian bodies that were being discovered. I don't think they set out to exclude Pluto specifically, but I could be wrong.
I'm not claiming they only wanted to exclude Pluto, but I think they did want to exclude it, because of its similarity to the other trans-Neptunians.

And why does calling them dwarf planets instead of planets make them easier to manage? I don't see that it does.
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Old 11th September 2018, 09:39 AM   #99
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Originally Posted by Ziggurat View Post
I already did. At some point, repetition becomes pointless.
Where did you explain why it's meaningless? Once you repeated that you said it, and now you say you've explained it.

But yes, repetition becomes pointless, so how about you break from that and make an actual argument for your suggestions? I honestly don't think it'd be hard for you to do. You just have to move beyond how things "feel".
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Old 11th September 2018, 09:40 AM   #100
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Originally Posted by Ziggurat View Post
I'm not claiming they only wanted to exclude Pluto, but I think they did want to exclude it, because of its similarity to the other trans-Neptunians.
Ok, got it.

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And why does calling them dwarf planets instead of planets make them easier to manage? I don't see that it does.
No, you're right on that. The name is dumb, as I've said.
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Old 11th September 2018, 09:51 AM   #101
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Originally Posted by Belz... View Post
Where did you explain why it's meaningless?
Do a search of this thread. You are the only person who has used this word.

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I honestly don't think it'd be hard for you to do. You just have to move beyond how things "feel".
Pointing out that something can cause confusion isn't a matter of feelings.
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Old 11th September 2018, 09:55 AM   #102
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Originally Posted by Ziggurat View Post
Do a search of this thread. You are the only person who has used this word.
Woah, sorry. I meant "misleading". That's quite a typo, there

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Pointing out that something can cause confusion isn't a matter of feelings.
But that it can cause confusion is a truism. That's true of literally any definition. I'm asking you to do more than just say "well, it shouldn't be like this". Why is it so hard?
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Old 11th September 2018, 10:01 AM   #103
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Originally Posted by Belz... View Post
Woah, sorry. I meant "misleading". That's quite a typo, there
Calling a planet like Jupiter a "dwarf planet" is misleading because the name suggests that it's small, but it's not. Is that really not obvious to you? We've been over this already.

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But that it can cause confusion is a truism. That's true of literally any definition.
But it's less true of some definitions than of others.

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I'm asking you to do more than just say "well, it shouldn't be like this". Why is it so hard?
I already have done more than that.
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Old 11th September 2018, 10:08 AM   #104
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Originally Posted by Ziggurat View Post
Calling a planet like Jupiter a "dwarf planet" is misleading because the name suggests that it's small, but it's not. Is that really not obvious to you? We've been over this already.
Yeah but the only problem is the name, not the classification. Change it to "planetoid" or "swatzherhaalt" and the problem goes away.

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But it's less true of some definitions than of others.
Sure, I'd buy that.

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I already have done more than that.
Well, I don't agree. I think that your suggestion for defining a planet is passable, but results in a large number of "planets" for the solar system, a number that will only grow with time. I think that your dislike for the "clearing the neighborhood" criterion is based on how it excludes Pluto rather than any pragmatic consideration.

All my attempts to have the discussion break beyond how things feel have failed, unfortunately. I'd really have liked us to find some common ground to discuss this. Clearly, astronomers would rather have an added layer of categorisation, and if we're to ditch the aforementioned criterion we'd need to replace it with one that's either less confusing, to use your own words, or more useful, to use mine.
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Old 11th September 2018, 10:20 AM   #105
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Seems like "spheroid under its own gravity" and "orbits a star" are all you need for an intuitive, historically-consistent definition. What's the problem with just using that?
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Old 11th September 2018, 10:24 AM   #106
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Originally Posted by Belz... View Post
Yeah but the only problem is the name, not the classification. Change it to "planetoid" or "swatzherhaalt" and the problem goes away.
The name is the classification. And "planetoid" would indeed reproduce the problem, since it also implies something smaller than a planet. "Swatzherhaalt" would not cause that problem, but it would produce others.

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Well, I don't agree. I think that your suggestion for defining a planet is passable, but results in a large number of "planets" for the solar system, a number that will only grow with time.
Yes, it would. Not once have you explained why this is a problem or a drawback.

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I think that your dislike for the "clearing the neighborhood" criterion is based on how it excludes Pluto rather than any pragmatic consideration.
That is not true. I have specifically outlined why I think it's a problem based on other reasoning.

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All my attempts to have the discussion break beyond how things feel have failed, unfortunately.
Your attempts have been weak, to put it charitably. When I point out that the cleared neighborhood definition can lead to confusion, you simply ignore it or pretend that it's a matter of feeling.

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I'd really have liked us to find some common ground to discuss this. Clearly, astronomers would rather have an added layer of categorisation, and if we're to ditch the aforementioned criterion we'd need to replace it with one that's either less confusing, to use your own words, or more useful, to use mine.
It's easy to add sub-categories to the category of planet. For example, gas giants, rocky planets, icy planets. You could even add dwarf planets as a sub-category. And these sub-categories don't even all have to be mutually exclusive, it's OK to have overlapping sub-categories.

I have an additional suggestion along those lines: icy dwarf planet. Put the threshold at the minimum mass a non-spinning rocky body would need in order for gravity to shape it hydrostatically. If an object is below that mass, then it won't achieve hydrostatic equilibrium if it's rocky, but it might if it's icy. This allows for non-dwarf icy planets, if they're big enough, but gives you a category for the small icy planets that wouldn't even be planets if they were rocky. Hell, you could even split planets and dwarf planets as separate mutually exclusive categories at this mass if you wanted. It would still be an improvement over the current definition.
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Old 11th September 2018, 10:31 AM   #107
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Originally Posted by Belz... View Post
All my attempts to have the discussion break beyond how things feel have failed, unfortunately.
I don't see how the discussion can possibly move beyond how things feel. "Planet" is essentially a literary classification.

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I'd really have liked us to find some common ground to discuss this. Clearly, astronomers would rather have an added layer of categorisation, and if we're to ditch the aforementioned criterion we'd need to replace it with one that's either less confusing, to use your own words, or more useful, to use mine.
Astronomers have feelings about the classification. You have feelings about replacing it. Ziggurat has feelings about replacing it.

But how about this? Instead of arguing with Ziggurat about his feelings, why not just state in your own terms the non-feelings-based common ground you have in mind? Maybe people will discuss your idea, maybe they won't. But at least you'll be presenting your idea as such, without depending on Ziggurat to follow your lead.
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Old 11th September 2018, 10:34 AM   #108
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Originally Posted by Ziggurat View Post
The name is the classification. And "planetoid" would indeed reproduce the problem, since it also implies something smaller than a planet.
I don't think that it does. "Planetoid" means "like a planet", not "small planet". After all, "humanoid" doesn't mean "small human".

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"Swatzherhaalt" would not cause that problem, but it would produce others.
I kind of like the sound of it, but I can propose more if you want!

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Yes, it would. Not once have you explained why this is a problem or a drawback.
I have, actually. I've explained that when you have a crapton of things in a category, we usually subdivide it because it makes it easier to work with.

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That is not true. I have specifically outlined why I think it's a problem based on other reasoning.
Ok then, aside from what it should be, or that it's misleading or confusing or whatever, which are all about how it feels, what reasoning have you proposed?

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When I point out that the cleared neighborhood definition can lead to confusion, you simply ignore it or pretend that it's a matter of feeling.
I'm trying to pin you down on something more specific. As I said, a LOT of words lead to confusion, but we still use them. Hell, "planet" is often confusing, and you're not proposing we drop the word altogether.

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It's easy to add sub-categories to the category of planet. For example, gas giants, rocky planets, icy planets. You could even add dwarf planets as a sub-category. And these sub-categories don't even all have to be mutually exclusive, it's OK to have overlapping sub-categories.
Agreed.

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I have an additional suggestion along those lines: icy dwarf planet. Put the threshold at the minimum mass a non-spinning rocky body would need in order for gravity to shape it hydrostatically. If an object is below that mass, then it won't achieve hydrostatic equilibrium if it's rocky, but it might if it's icy. This allows for non-dwarf icy planets, if they're big enough, but gives you a category for the small icy planets that wouldn't even be planets if they were rocky. Hell, you could even split planets and dwarf planets as separate mutually exclusive categories at this mass if you wanted. It would still be an improvement over the current definition.
Ok so how about "major planet" and "minor planet" or something along those lines?
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Old 11th September 2018, 10:47 AM   #109
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Originally Posted by Samson View Post
While this might be regarded as a fun thread, scientific input would be appreciated. I thought the relegation was a disgrace at the time, but New Horizon laid proof like an EGG.
Your use of the word 'disgrace' is what turns this from a scientific discussion to an emotional one. And that necessarily opens up the possibility that some will find such an emotional reaction to be comical.
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Old 11th September 2018, 10:58 AM   #110
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Originally Posted by Belz... View Post
I don't think that it does. "Planetoid" means "like a planet", not "small planet". After all, "humanoid" doesn't mean "small human".
Except that the number of factors which can disqualify something that is like a planet from actually being a planet are much more limited. A moon can be like a planet but not a planet, but we've already got a name for those, so they shouldn't be planetoids. An object can be like a planet but too big to be a planet, in which case it turns into a brown dwarf, so that's not a planetoid either. If you take the IAU's definition, then it could be like a planet except it hasn't cleared its neighborhood. That's a case where the term might work, but nobody seems to like that criteria, and if we discard it (as I hope we do), then that's not a case where the term would be used. Which pretty much just leaves us with an object being too small, like Vesta.

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I have, actually. I've explained that when you have a crapton of things in a category, we usually subdivide it because it makes it easier to work with.
But subdivision is easy in this case.

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Ok then, aside from what it should be, or that it's misleading or confusing or whatever, which are all about how it feels
If you want to say that trying to avoid confusion is just about feels, then any possible motive you can have for doing anything is just about feels, including not wanting to overload a category with members in order to make it easier to work with.

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Ok so how about "major planet" and "minor planet" or something along those lines?
Sure, such a division would be easy and practical, as long as the difference is something sensible like mass or size.
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Old 11th September 2018, 11:03 AM   #111
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Originally Posted by Ziggurat View Post
Except that the number of factors which can disqualify something that is like a planet from actually being a planet are much more limited. A moon can be like a planet but not a planet, but we've already got a name for those, so they shouldn't be planetoids.
No, no. I meant bodies that orbit the sun, have hydrostatic equilibrium, but don't meet the other requirements, whatever they may be. Essentially replacing the word "dwarf planet" with something else.

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If you want to say that trying to avoid confusion is just about feels, then any possible motive you can have for doing anything is just about feels, including not wanting to overload a category with members in order to make it easier to work with.
That's not my point. My point is demonstrating that it's confusing to more than just you or me. Is it confusing for astronomers? They're the ones dealing with these terms on a daily basis.

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Sure, such a division would be easy and practical, as long as the difference is something sensible like mass or size.
See, I knew we could agree on something.
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Old 11th September 2018, 11:15 AM   #112
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Originally Posted by Belz... View Post
That's not my point. My point is demonstrating that it's confusing to more than just you or me. Is it confusing for astronomers? They're the ones dealing with these terms on a daily basis.
Primary school educators have to deal with the term "planet" a lot as well. And I think it would be beneficial if they were using the terms the same way. That's not always possible in science (temperature is an example: the actual definition is much more subtle than the popular definition, and must be so by necessity), but I think it is possible here.
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Old 11th September 2018, 11:23 AM   #113
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Originally Posted by Belz... View Post

Ok so how about "major planet" and "minor planet" or something along those lines?
Now you are back to planets and dwarf planets both being planets.

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Pluto is was and always will be a planet
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Old 11th September 2018, 11:24 AM   #114
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Anyone that knows about the Kuiper Belt that thinks Pluto is a planet is leaving in a fantasy solar system full of rainbow farting unicorns.

I figured out pluto wasn't a planet 20 years ago.

Pluto is not, never was, and never will be a planet.
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Old 11th September 2018, 11:30 AM   #115
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Originally Posted by Belz... View Post
...Essentially replacing the word "dwarf planet" with something else...
"Aplanet"?
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Old 11th September 2018, 11:35 AM   #116
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Originally Posted by Ziggurat View Post
Primary school educators have to deal with the term "planet" a lot as well. And I think it would be beneficial if they were using the terms the same way. That's not always possible in science (temperature is an example: the actual definition is much more subtle than the popular definition, and must be so by necessity), but I think it is possible here.
That's fair.

Personally, and again I'm not an astronomer, I find the word "dwarf planet" confusing specifically because it seems to indicate that it's a type of planet when it's not. Also, as discussed earlier I dislike the 'clearing the neighborhood' criterion, but aside from the fact that I find it confusing for myself, it's actually pretty hard to determine, and there's also the issue of the trojans.

So I agree that hydrostatic equilibrium and primary orbit around a star should be the main criteria, if only because it's how the word's been understood for centuries. However, in order to keep the number of planets down, and since we seem to agree that primary school teachers and students have to deal with the list also, I'd split between major planets and minor planets (or planets and planetoids, as per my previous suggestion), with the difference being based on mass (which will necessarily be arbitrary but could be around 1/20th earth masses, for instance) and orbital characteristics (there are important differences of size, mass, composition and orbit between the Kuiper belt bodies, whose orbits look like something drawn by a madman, and those more massive ones that are relatively close to the sun and in near-circular motions.).
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Old 11th September 2018, 11:37 AM   #117
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Originally Posted by Red Baron Farms View Post
Now you are back to planets and dwarf planets both being planets.
Yes, I'm discussing a compromise. I know, I know, that's heresy on the internet.

Personally I'd just call the non-major ones "planetoids" or something to that effect: they are like planets but not planets, while the irregularily-shaped bodies would just be asteroids.
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Old 11th September 2018, 11:40 AM   #118
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Originally Posted by Belz... View Post
However, in order to keep the number of planets down, and since we seem to agree that primary school teachers and students have to deal with the list also, I'd split between major planets and minor planets, with the difference being based on mass (which will necessarily be arbitrary but could be around 1/20th earth masses, for instance) and orbital characteristics (there are important differences of size, mass, composition and orbit between the small, icy bodies whose orbits look like something drawn by a madman, and those more massive ones that are relatively close to the sun and in near-circular motions.).
Mass or size is better than orbital characteristics like eccentricity, because it makes for smoother extension to other solar systems, where very large planets might have high eccentricities or small planets could have small eccentricities. Mass is probably better than size because it's usually easier to measure, at least within our solar system.
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Old 11th September 2018, 11:44 AM   #119
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Originally Posted by Ziggurat View Post
Mass or size is better than orbital characteristics like eccentricity, because it makes for smoother extension to other solar systems, where very large planets might have high eccentricities or small planets could have small eccentricities. Mass is probably better than size because it's usually easier to measure, at least within our solar system.
Yes, you're right. It's biased towards our own solar system.

But then, we don't know how other systems are built. Maybe planets their stars are pretty much always in a near-circular orbit and this wouldn't be a problem. For now it's the only system for which we have reliable data.
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Old 11th September 2018, 12:20 PM   #120
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Originally Posted by Belz... View Post
Yes, you're right. It's biased towards our own solar system.

But then, we don't know how other systems are built. Maybe planets their stars are pretty much always in a near-circular orbit and this wouldn't be a problem. For now it's the only system for which we have reliable data.
Our data is limited and we don't know how representative it is, but there are a lot of exoplanets with eccentricities larger than Haumea (0.19), Makemake (0.15), Pluto (0.25), and even Eris (0.44), and even a few that exceed the eccentricity of Sedna (0.85). At the extreme end, the exoplanet HD 20782 b has an eccentricity of 0.97 and an estimated mass of 1.8 Jupiters. We can't extrapolate reliable statistics about exoplanet eccentricities because of the possibility of sampling bias, but there are certainly at least some cases of large planets with high eccentricities out there.

ETA: Runner up for extreme exoplanet eccentricity goes to HD 80606 b, which has an eccentricity of 0.93 and a mass of 4 Jupiters.
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