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Old 11th September 2018, 11:38 PM   #121
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Originally Posted by Ziggurat View Post
No. You can classify the largest body in the co-orbiting group as the planet and the smaller ones as moons.

Unless of course it is a binary where the difference in size between the two is not statistically significant (meaning they have a mass ratio extremely close to 1; something > .9, maybe > .8, should be close enough).*

Then they should both be considered planets if they otherwise classify. Anything less and one is a moon IMO. (Some scientists have actually proposed that smaller mass ratio systems should be considered double planets. Those scientists are smelly & dumb and, most importantly, wrong. )

But from what we know about the formation and evolution of solar systems they (mass ratios near 1) should be extremely rare. So improbable in fact that the term Double Planet is not even officially recognized by the IAU.

Nothing in our solar system comes even close. The closest is Pluto–Charon with a mass ratio of .11 or so (Earth-Moon being like .011, and the gas giants and there moons being like .00011). Nothing in any solar system we discover should come even close to it.

But because of the size of the universe, we should assume they do exist.**




*Not to be confused with merely being a binary system where the bodies orbit a point clearly outside of either body (their barycenter).


**A neat statistical side effect of the unfathomable size of the universe. There are some extremely low probability things that it should be basically impossible for us to find in any random solar system, or even galaxy. But yet because of the insane size of the universe, they are somewhere. (And, unfortunately, guess what is very likely one of those things? Intelligent sentient life.)
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Old 12th September 2018, 02:03 AM   #122
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I actually wouldn't mind a simpler definition of planet that includes large moons, like the Moon, and rogue planets that don't orbit a star. Basically just a simple definition that's based on the object itself and isn't related to it's movement or environment.
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Old 12th September 2018, 06:24 AM   #123
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Originally Posted by Roboramma View Post
I actually wouldn't mind a simpler definition of planet that includes large moons, like the Moon, and rogue planets that don't orbit a star. Basically just a simple definition that's based on the object itself and isn't related to it's movement or environment.
Planet: Spherical, orbits a star. Rogue planet: Would be a planet, but no star. Moon: Orbits a planet.

If the bizarre criteria of "easy for school children to remember them all" (a criteria we don't apply to literally anything else - stars, mountains, rivers, fish, countries, states, presidents, wars, etc), then... Planet: One of the original nine so named in the Solar system. Good luck remembering all the millions of non-planet "planets" out there, chump schoolteachers!

Seriously, Belz... What's with this 'think of the schoolchildren' crap? Is there anything that would convince you to renounce it as a terrible criteria?
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Old 12th September 2018, 06:36 AM   #124
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There were 7 original planets, and the sun and moon were members.

Then Yoko came along.
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Old 12th September 2018, 06:42 AM   #125
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Originally Posted by theprestige View Post
Seriously, Belz... What's with this 'think of the schoolchildren' crap? Is there anything that would convince you to renounce it as a terrible criteria?
I don't know. Is there anything that would convince you to renounce your strawman?

Hell, even Ziggurat brought it up. The point is that when we create a definition for something, it's either to reflect usage or, in the case of technical things, to serve specific purposes. So what's the purpose of the term "planet"? Well, for one it serves to help astronomers and astrophysicists distinguish them from other stuff and work with them in their theories, calculations and observations, and for another it helps us plebs learn about them, including our kids who have to learn them at school. And about the second, well if you want kids to learn the planets, which sounds like a good idea, you'll have a hard time getting that done if there are 6891 planets in the solar system.
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Old 12th September 2018, 06:42 AM   #126
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Originally Posted by Ziggurat View Post
There were 7 original planets, and the sun and moon were members.

Then Yoko came along.
John Lennon liked strong moons.
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Old 12th September 2018, 07:13 AM   #127
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It's a shame that the real scientists got involved in this. Science fiction types had this sorted years ago.

Any body large enough to pull itself into a spheroid was a planetary body, unless it was so large that fusion had begun, in which case it's a star.

Planetary bodies that orbit stars are planets.

Planetary bodies that orbit planets are planetary moons.

Planetary bodies that share a barycenter orbit outside the other planetary body's surface are double planets.

Planetary bodies that travel freely, not orbiting other bodies are rogue planets.

Doc Smith, through Star Trek, we agreed on these things.
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Old 12th September 2018, 07:21 AM   #128
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Feet to the fire even lumping Mercury/Venus/Earth/Mars and Jupiter/Saturn/Uranus/Neptune into the same category feels weird to me.

I'm perfectly okay with the statement "As of this moment the major bodies of the solar system other than the Sun are 4 rocky planets, 4 gas giant planets, and 5 dwarf planets and those numbers and categories could change as our knowledge of the solar system increases."
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Old 12th September 2018, 07:37 AM   #129
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Originally Posted by This is The End
Nothing in our solar system comes even close. The closest is Pluto–Charon with a mass ratio of .11 or so (Earth-Moon being like .011, and the gas giants and there moons being like .00011). Nothing in any solar system we discover should come even close to it.

True for all the planets, dwarf planets, and moons so far discovered in the Solar System, but not true for "one" (or should that be two ?) of the largest of the Jupiter trojan asteroids, 617 Patroclus. This was discovered in 1906, and in 2001 was observed to consist of two almost equally sized bodies, each about 100 km in diameter, orbiting around their common centre of mass in a roughly circular orbit 680 km apart.
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Old 12th September 2018, 07:45 AM   #130
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Originally Posted by Pope130 View Post
It's a shame that the real scientists got involved in this. Science fiction types had this sorted years ago.
Yeah, but in the real world you have a number of edge cases and other issues that need the be addressed and that fiction can ignore.
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Old 12th September 2018, 07:54 AM   #131
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The word 'planet' is Ancient Greek, meaning 'wanderer' - and was originally applied to differentiate the few moving lights in the sky from all the other 'fixed stars' which, over normal human time scales, remain in fixed positions relative to each other.

So, using the original meaning of the word, it was quite correct to include the Sun and the Moon in with what we now consider to be planets.
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Old 12th September 2018, 08:16 AM   #132
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Originally Posted by ceptimus View Post
The word 'planet' is Ancient Greek, meaning 'wanderer' - and was originally applied to differentiate the few moving lights in the sky from all the other 'fixed stars' which, over normal human time scales, remain in fixed positions relative to each other.

So, using the original meaning of the word, it was quite correct to include the Sun and the Moon in with what we now consider to be planets.
Yeah but by the same token that'd include asteroids and specs of dust.
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Old 12th September 2018, 08:19 AM   #133
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Not really - because the ancients didn't have telescopes, so they could only see naked-eye objects.
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Old 12th September 2018, 08:28 AM   #134
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Originally Posted by ceptimus View Post
Not really - because the ancients didn't have telescopes, so they could only see naked-eye objects.
Irrelevant. We're talking about how the word is defined. If we're to keep the definition, we have to apply it to the objects we know of now.
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Old 12th September 2018, 10:01 AM   #135
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Originally Posted by Belz... View Post
I don't know. Is there anything that would convince you to renounce your strawman?
You're right. I'm sorry.

So. I definitely used some uncalled-for hyperbole, but this:

Originally Posted by Belz... View Post
if you want kids to learn the planets, which sounds like a good idea, you'll have a hard time getting that done if there are 6891 planets in the solar system.
Is not a straw man. And there's a few things to say about it.

One thing to say is, "sounds like a good idea" is an argument from feelings, which elsewhere in the thread you seem to oppose.

Another thing: Do we want kids to learn the planets? One thing your argument does for me is cause me to question the basic premise. So what if kids don't learn the planets right away?It's not like the planets are going anywhere. It's not like anyone needs to know their names and numbers to get through life. My sister made it all the way to high school thinking the sun and the moon were the same size, which is very silly but also entirely inconsequential.

It's also special pleading. We want kids to learn countries and presidents and mountains and rivers and stars, but we don't dumb down the definitions of these things to make it easier on their child brains.

"Planets are spherical under their own gravity - you'll learn more about that next year, Johnny - and orbit a star. There are seven planets in our sky that were visible to the naked eye, and named by the ancients. There are two more planets that were found by telescopes in the past couple hundred years. Since then, we have found a handful more planets in our solar system, as well as additional planets orbiting other stars. Here's a list of books in the library that you can read, if you're interested in learning more about all these planets."

"Mountains are numerous. Here's a few of local or historical interest to get your brain juices flowing. Here's some books in the library you can check out if you're interested in learning more about mountains."

"This country has had 45 presidents, with more to come. You don't have to memorize all of them, but refer to the poster on the back wall of the classroom if you'd like to try. Meanwhile, here's a few that have special historical significance, and here's a list of library books..."

Etc.

The way I see it, teaching children about the planets is not terribly important after all, and having a large number of planets in the catalog is no real impediment to such teaching if you decide you'd like to do that.
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Old 12th September 2018, 10:06 AM   #136
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Originally Posted by Belz... View Post
Irrelevant. We're talking about how the word is defined. If we're to keep the definition, we have to apply it to the objects we know of now.
Why? You're stating these rules like they're fundamental principles or immutable laws.
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Old 12th September 2018, 10:10 AM   #137
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Originally Posted by Belz... View Post
IWell, for one it serves to help astronomers and astrophysicists distinguish them from other stuff and work with them in their theories, calculations and observations
Does it really, though? Is that an argument that Tyson has actually put forth - that it's easier for him to do planetology if he doesn't have to think of Pluto as a planet? As JoeMorgue implies, it seems like he'd still be stuck on Mars and Jupiter both being "planets", not trying to wrap his head around Pluto.
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Old 12th September 2018, 10:16 AM   #138
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The only Pluto I know is a cartoon character from Disney's.


I know the planet Plutón, which they tried to demote, but as the ending -ón tells, it's a humongous thing, so it's still a planet. There's no printed item in my home telling otherwise.
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Old 12th September 2018, 10:19 AM   #139
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Originally Posted by theprestige View Post
Planet: Spherical, orbits a star. Rogue planet: Would be a planet, but no star. Moon: Orbits a planet.
Sure, that works. I just think there's something more elegant about the idea that anything like the earth would be a planet, no matter where it ends up.

"Like the earth" of course doesn't mean identical to the earth, and we can go back and forth about how different from the earth something can be without wanting to have a different category.

Maybe "like the earth" shouldn't even be the criterion. That's just what I found when I thought about what a planet is to me and why I would want one thing or another included in that definition. Someone could present an argument for a better way of thinking about what planets are and I might be swayed by it.

If the earth's orbit was perturbed to the point where it was expelled from the solar system I think I'd still consider it a planet, and similarly if it somehow ended up orbiting Jupiter.
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Old 12th September 2018, 10:22 AM   #140
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Originally Posted by theprestige View Post
One thing to say is, "sounds like a good idea" is an argument from feelings, which elsewhere in the thread you seem to oppose.
Ok, call it a reasonable thing to do, since knowing about the universe is part of teaching children about the world around us. The result is the same: sounds like a good idea to me.

Quote:
Another thing: Do we want kids to learn the planets?
Yes, because if you throw general topics at them early on, not only will that equip them with all sorts of knowledge that may come in handy, and allow them to understand things from at least a basic perspective, but it also will open doors to them, and potentially interest them in a future career.

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It's also special pleading. We want kids to learn countries and presidents and mountains and rivers and stars, but we don't dumb down the definitions of these things to make it easier on their child brains.
No but you exclude streams from the rivers category, don't you?

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Why? You're stating these rules like they're fundamental principles or immutable laws.
I don't understand your objection. I was responding to ceptimus' post about keeping the original definition of planet. If we keep it, then it would apply to what we know now of our solar system. Otherwise we have to alter the definition to excluse the other "wanderers" we've discovered and we're right back to square one.

Quote:
Does it really, though?
I think so. All professions have categories of this or that so you can classify them to simplify language and operations. Why do you think it would be different here?
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Old 12th September 2018, 10:28 AM   #141
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Definitions are never about limiting the number of members in a category. They are about clarifying distinctions between members. There really is a difference between Mammals and Birds, both form separate clades, and that's the reason for those separate categories.

These categories should about identifying meaningful patterns in nature. The difference between a planet and a star is an important such distinction. Contrary to what I said in my last post the difference between planets and moons is also a meaningful distinction in understanding the dynamics of the solar system.

Finding a category that helps to give us insight into nature seems like a reasonable way to go about defining categories.
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Old 12th September 2018, 10:31 AM   #142
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Originally Posted by Roboramma View Post
Definitions are never about limiting the number of members in a category. They are about clarifying distinctions between members.
And yet they changed the definition of 'planet' to limit the number of members in the category.
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Old 12th September 2018, 11:00 AM   #143
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Originally Posted by Belz... View Post
Originally Posted by theprestige View Post
Another thing: Do we want kids to learn the planets?
Yes, because if you throw general topics at them early on, not only will that equip them with all sorts of knowledge that may come in handy, and allow them to understand things from at least a basic perspective, but it also will open doors to them, and potentially interest them in a future career.
Sure. But do they need to know all the planets for that purpose? I don't see that they do. I think suffices to teach them some subset of "important" planets, and then let them know there are some more smaller ones out there.

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No but you exclude streams from the rivers category, don't you?
Depends on who's doing the defining. For example, the United States Board on Geographic Names defines rivers as a subset of stream, which is basically any linear flowing body of water and thus includes rivers, creeks, brooks, etc.
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Old 12th September 2018, 11:16 AM   #144
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Originally Posted by Ziggurat View Post
Sure. But do they need to know all the planets for that purpose? I don't see that they do. I think suffices to teach them some subset of "important" planets, and then let them know there are some more smaller ones out there.
Sure. How do we determine which ones, and do they deserve a separate category, while we're at it?

Quote:
Depends on who's doing the defining. For example, the United States Board on Geographic Names defines rivers as a subset of stream, which is basically any linear flowing body of water and thus includes rivers, creeks, brooks, etc.
Yes but the point is that not all streams are rivers. And in some languages you have additional categories.
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Old 12th September 2018, 11:41 AM   #145
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Originally Posted by Giordano View Post

Did you know that not drawing pants on Pluto was okay because he did not speak and was presented as a dog/pet, whereas drawing pants on Goofy was considered crucial for decorum because he speaks in the cartoons and therefore was human-enough to need clothes. Presumably Goofy's ancestors ate of the fruit of knowledge in Eden; Pluto's did not.
Donald Duck could speak but did not wear either pants or trousers.
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Old 12th September 2018, 12:08 PM   #146
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When the IAU says Pluto ain't a planet you say how high!
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Old 12th September 2018, 12:21 PM   #147
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Originally Posted by jeremyp View Post
Donald Duck could speak but did not wear either pants or trousers.
But did wear a towel when he got out of the shower.
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Old 12th September 2018, 12:23 PM   #148
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Originally Posted by Elagabalus View Post
When the IAU says Pluto ain't a planet you say how high!
No, you say "how many astronomical units?"
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Old 12th September 2018, 12:32 PM   #149
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Originally Posted by Roboramma View Post
Sure, that works. I just think there's something more elegant about the idea that anything like the earth would be a planet, no matter where it ends up.

"Like the earth" of course doesn't mean identical to the earth, and we can go back and forth about how different from the earth something can be without wanting to have a different category.

Maybe "like the earth" shouldn't even be the criterion. That's just what I found when I thought about what a planet is to me and why I would want one thing or another included in that definition. Someone could present an argument for a better way of thinking about what planets are and I might be swayed by it.

If the earth's orbit was perturbed to the point where it was expelled from the solar system I think I'd still consider it a planet, and similarly if it somehow ended up orbiting Jupiter.
For sure. I don't know if I've already said it in this thread, but for the past couple days I've been thinking it: "Planet" is really more of a literary term than a scientific one. Which is why reclassifying Pluto is referred to as a "demotion", and why the Tyson/IAU push to reclassify it has more of a Showboaty McShowboatface feel to it than a "good science done well" feel to it.
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Old 12th September 2018, 01:00 PM   #150
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Originally Posted by Belz... View Post
Ok, call it a reasonable thing to do, since knowing about the universe is part of teaching children about the world around us. The result is the same: sounds like a good idea to me.
Calling it reasonable doesn't make it reasonable. I'll call it the reasonable thing to do if there's a convincing argument from reason to support it.

In general, we don't create definitions for the purpose of reducing the number of things schoolchildren have to deal with. Maybe you think that stars are an important part of the universe that children should be taught. Are you suggesting we should maybe redefine "star" to mean "O-class stars on the Hertzprung-Russel" diagram? Those are the least common class of stars, so it would ease the burden on schoolteachers for sure.

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Yes, because if you throw general topics at them early on, not only will that equip them with all sorts of knowledge that may come in handy, and allow them to understand things from at least a basic perspective, but it also will open doors to them, and potentially interest them in a future career.
Stipulated.

What is wrong with this as a general concept?

Planets are spherical under their own gravity, and orbit stars. Asteroids orbit stars, but don't have the mass to form into spheres. Moons may or may not be spherical, and orbit planets. There are a few planets in our solar system that you can see with the naked eye, and many more besides. Here's a few notable planets to get you started. If you decide to pursue the subject, you'll find there's some edge cases, which are probably the most interesting part.
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No but you exclude streams from the rivers category, don't you?
I can't say that I've ever been so committed to enumerating rivers to children that I've had to exclude streams just to make the numbers more manageable. I think you're making Introductory Natural Science waaay more complicated than it needs to be.

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I don't understand your objection. I was responding to ceptimus' post about keeping the original definition of planet. If we keep it, then it would apply to what we know now of our solar system. Otherwise we have to alter the definition to excluse the other "wanderers" we've discovered and we're right back to square one.
Noted. Fair enough.

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I think so. All professions have categories of this or that so you can classify them to simplify language and operations. Why do you think it would be different here?
You think so, but what has Tyson/IAU actually said about it?
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Old 12th September 2018, 03:12 PM   #151
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Originally Posted by Belz...
Originally Posted by Elagabalus View Post
When the IAU says Pluto ain't a planet you say how high!
No, you say "how many astronomical units?"

Leave it in "how many nanoseconds light?"
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Old 12th September 2018, 04:29 PM   #152
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I prefer the Daly Show solution to the "Is Pluto A Planet" question.
Would Galactus have it for Lunch?
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Old 12th September 2018, 06:00 PM   #153
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Originally Posted by Belz... View Post
And yet they changed the definition of 'planet' to limit the number of members in the category.
And if that's the reason for the redefinition, I think it's a bad reason.

If on the other hand someone said: "Damn, this definition includes many bodies that really don't seem to fit what we meant by planet when we originally came up with it, let's try to look more closely at what that category is trying to define and make a more rigorous definition." that would make sense.

Since that doesn't seem to be what happened, I think what you say above is a good case for why the new definition isn't particularly good. It's not based on some important distinction in the world.
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Old 12th September 2018, 06:28 PM   #154
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Originally Posted by dudalb View Post
I prefer the Daly Show solution to the "Is Pluto A Planet" question.
Would Galactus have it for Lunch?
The Daily Show is an ally of Big Science and Neil Degrasse Tyson. They're pandering to comic book nerds because reasons. Boop to that.
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Old 12th September 2018, 06:48 PM   #155
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Originally Posted by Ziggurat View Post
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.
Why? What is it about the label "planet" that makes it inherently more valuable to you?
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Old 12th September 2018, 07:24 PM   #156
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Originally Posted by arthwollipot View Post
Why? What is it about the label "planet" that makes it inherently more valuable to you?
Does it matter? That part was just a statement of personal opinion. It's not actually part of my argument for changing the definition.
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Old 12th September 2018, 07:27 PM   #157
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Originally Posted by Ziggurat View Post
Does it matter? That part was just a statement of personal opinion. It's not actually part of my argument for changing the definition.
I think it does matter. You appear to be putting stock in the label "planet" that the label "dwarf planet" does not have. You appear to be implying that it is better to have the "planet" label than to have the "dwarf planet" label.

If that is not the case, and your argument is about nothing but process, then I apologise and withdraw my question.
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Old 13th September 2018, 12:20 AM   #158
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Originally Posted by Belz... View Post
Irrelevant. We're talking about how the word is defined. If we're to keep the definition, we have to apply it to the objects we know of now.
No we don't. The easiest way to get everyone alongside with a new definition would be to say "historically we have 9 bodies that we call planets, for any future body to be considered a planet it needs to meet the following criteria...." Then purists could say under their breaths "drawf planet" when anyone calls Pluto a planet and Plutophiles can under their breaths say "yes a planet" when Pluto is described as a drawf planet.
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Old 13th September 2018, 02:41 AM   #159
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Originally Posted by theprestige View Post
Calling it reasonable doesn't make it reasonable.
Now you're moving the goalposts. You objected that my wording was inadequate, now you're ignoring that and switching to a different line. It almost seems like you want to find a reason to disagree.

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In general, we don't create definitions for the purpose of reducing the number of things schoolchildren have to deal with.
Who cares what the general case is? Read up on why they changed the definition.

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What is wrong with this as a general concept?
I've already explained why several times, prestige. It would result in a great number of planets, possibly hundreds or thousands, depending on how many we eventually fine, and the IAU wanted to avoid that.

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I can't say that I've ever been so committed to enumerating rivers to children that I've had to exclude streams just to make the numbers more manageable. I think you're making Introductory Natural Science waaay more complicated than it needs to be.
No, I'm using a parallel to illustrate the point but somehow you missed it.

Noted. Fair enough.

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You think so, but what has Tyson/IAU actually said about it?
Do you acknowledge and agree with my argument there?
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Old 13th September 2018, 02:43 AM   #160
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Originally Posted by Roboramma View Post
And if that's the reason for the redefinition, I think it's a bad reason.
Sounds like as good a reason as anything. Definitions are arbitrary and can reflect a great number of purposes or incentives.

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If on the other hand someone said: "Damn, this definition includes many bodies that really don't seem to fit what we meant by planet when we originally came up with it, let's try to look more closely at what that category is trying to define and make a more rigorous definition." that would make sense.
I've also argued that it is also the case that trans-neptunian bodies are different in many respects to the canonical eight.

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Since that doesn't seem to be what happened, I think what you say above is a good case for why the new definition isn't particularly good.
That sounds a bit circular. You've defined 'good' as excluding that reason, and then used that to call it bad.
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