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Main
Date: 25 Aug 2006 11:53:50
From: Willie R. Meghar
Subject: Of Stars, Pluto and Planetary Classification
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The "Planet" Problem:
The IAU has come up with a planetary classification scheme that is
*not* based solely upon the physical nature of the objects being
classified. The orbital details of an otherwise qualified body can
exclude it from the "planet" classification.
This means a body can be planet if located in one orbit (and
gravitationally bound to one star) while an identical body would fail
to be classified as a planet if located in a different orbit (or
gravitationally bound to a different star).
Furthermore, the IAU classification scheme cannot be applied to bodies
orbiting stars other than the Sun. This ignores the vast majority of
potential planetary bodies.
About Stars:
Stars remain stars regardless of where they are. A star in orbit
about another star is still a star. This is the case regardless of
anything occupying a nearby orbit. This is the case even if other
stars occupy the same orbit. Even a star found between two widely
separated galaxies would still be a star.
Concerning Pluto:
Current events have placed Pluto on center stage. Either Pluto is a
planet or Pluto is not a planet. Some favor one outcome. Some favor
the other outcome. A planetary classification scheme should *not* be
dored to specifically include nor to specifically exclude Pluto as
a planet. The classification scheme needs to be more objective.
Concerning the Number of Planets:
A planetary definition should not be judged on how many or how few
planets our solar system contains. Four planets or four hundred
planets -- it makes no difference so long as all qualified bodies are
included and all unqualified bodies are excluded.
Properties of a Good Planetary Definition:
1) It should be based solely upon one or more (preferably easily
determined) physical property of the candidate body.
2) It should permit all qualifying bodies to remain planets
regardless of where they are and regardless of where nature or future
technology might move them (with due allowances for boiling off mass,
etc.)
3) The cut-off between planet and non-planet should not be arbitrary.
It should be based upon a real, naturally occurring, physical
transition.
4) It should be applicable to our own solar system as well as to
extra-solar planetary systems.
Further Thoughts on a Planetary Definition or Planetary Classification
Scheme:
In light of the above points, the upper cut-off point could be related
to thermonuclear fusion. We wouldn't want to include stars as
planets! Optionally, (and recommended) a transition classification
could also be included.
The lower cut-off point could be related to the mass associated with
the transition between reasonably spherical and reasonably
non-spherical objects. Once agreed upon, the cut-off *mass* (not the
degree of sphericalness) will be the deciding factor. Optionally,
(and recommended) a transition classification (specifying a range of
mass) could also be included.
If so desired, the classification "Planet" could be subdivided into
Classes, with each class having upper and lower mass limits.
Pay no special attention to Pluto! Let it fall wherever in (or
outside) the definition or classification scheme. Pay no special
attention to orbits! (See "About Stars" above.). It's the physical
body we're interested in, regardless of where that body might be
found. If this means that some planetary satellites are also Planets,
then so be it!
It's not the job of science to keep the number of planets in our solar
system small for easy memorization by school children. It's more
important to have definitions and classification schemes that science
and astronomy can be proud of.
Willie R. Meghar
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Date: 25 Aug 2006 12:43:35
From: AustinMN
Subject: Re: Of Stars, Pluto and Planetary Classification
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Willie R. Meghar wrote:
<snip >
> About Stars:
>
> Stars remain stars regardless of where they are. A star in orbit
> about another star is still a star. This is the case regardless of
> anything occupying a nearby orbit. This is the case even if other
> stars occupy the same orbit. Even a star found between two widely
> separated galaxies would still be a star.
This applies elsewhere. Things are what they are, and only rarely do
they change what they are because of their location. A watch is a
watch whether it's on the retailer's shelf, strapped to my wrist, or in
a thief's pocket. It's a watch wheter or not it has a jeweled
movement, digital movement (yes, there have been such things), a
quartz oscillator, or some other mechanism for keeping time. It takes
very special circumstances for it's location to have an impact. Under
the wheels of a bus, it stops being a watch and becomes a piece of
junk, not because of it's location, but because the bus did something
dramatic to it, changing the nature of what it was.
<snip >
> Pay no special attention to Pluto! Let it fall wherever in (or
> outside) the definition or classification scheme. Pay no special
> attention to orbits! (See "About Stars" above.). It's the physical
> body we're interested in, regardless of where that body might be
> found. If this means that some planetary satellites are also Planets,
> then so be it!
>
> It's not the job of science to keep the number of planets in our solar
> system small for easy memorization by school children. It's more
> important to have definitions and classification schemes that science
> and astronomy can be proud of.
I think the real problem is trying to put a scientific definition to a
non-scientific term. Astronomers typically don't use the term
"shooting star" because it is a non-scientific term. Instead, new
terms were invented and defined. It makes no sense to try to define
"shooting star" scientifically because it is such a misleading term.
What's really needed is a new term (or, more likely, a set of new
terms) to define non-star bodies in space. I think astronomers need to
stop using the term "planet" exept when dealing with the public. We
figured out that calling man-made sattelites "moons" was not
appropriate, perhaps even before there were any.
Maybe it's time to throw out the term "planet" and replace it with a
new set of terms rather than try to force a scientific definition on a
term that has long outlived it's scientific usefulness.
Austin
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Date: 25 Aug 2006 14:37:54
From: Brian Tung
Subject: Re: Of Stars, Pluto and Planetary Classification
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AustinMN wrote:
> What's really needed is a new term (or, more likely, a set of new
> terms) to define non-star bodies in space. I think astronomers need to
> stop using the term "planet" exept when dealing with the public.
I think that is exactly why they wanted a definition--so that when some
new object was discovered, they would be able to agree on one of the
following:
"It is a planet."
"It is not a planet."
"We haven't made enough observations of it (and possibly its
environment) to be sure. When we have, we'll know."
And to avoid either utter disagreement and chaos, or agreement on the
following non-answer:
"Well, that depends on what you call a planet..."
In research papers, the term planet is used casually. The objects under
study are referred to specifically. Hardly any paper examines the major
planets as a whole.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 25 Aug 2006 15:00:34
From: Willie R. Meghar
Subject: Re: Of Stars, Pluto and Planetary Classification
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"AustinMN" wrote:
>I think the real problem is trying to put a scientific definition to a
>non-scientific term. Astronomers typically don't use the term
>"shooting star" because it is a non-scientific term. Instead, new
>terms were invented and defined. It makes no sense to try to define
>"shooting star" scientifically because it is such a misleading term.
>
>What's really needed is a new term (or, more likely, a set of new
>terms) to define non-star bodies in space. I think astronomers need to
>stop using the term "planet" exept when dealing with the public. We
>figured out that calling man-made sattelites "moons" was not
>appropriate, perhaps even before there were any.
>
>Maybe it's time to throw out the term "planet" and replace it with a
>new set of terms rather than try to force a scientific definition on a
>term that has long outlived it's scientific usefulness.
Yes, this makes a great deal of sense!
Willie R. Meghar
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Date: 26 Aug 2006 11:50:26
From: Carsten A. Arnholm
Subject: Re: Of Stars, Pluto and Planetary Classification
|
Willie R. Meghar wrote:
> "AustinMN" wrote:
>
>> I think the real problem is trying to put a scientific definition to
>> a non-scientific term. Astronomers typically don't use the term
>> "shooting star" because it is a non-scientific term. Instead, new
>> terms were invented and defined. It makes no sense to try to define
>> "shooting star" scientifically because it is such a misleading term.
>>
>> What's really needed is a new term (or, more likely, a set of new
>> terms) to define non-star bodies in space. I think astronomers need
>> to stop using the term "planet" exept when dealing with the public.
>> We figured out that calling man-made sattelites "moons" was not
>> appropriate, perhaps even before there were any.
>>
>> Maybe it's time to throw out the term "planet" and replace it with a
>> new set of terms rather than try to force a scientific definition on
>> a term that has long outlived it's scientific usefulness.
>
> Yes, this makes a great deal of sense!
>
> Willie R. Meghar
Let us test this. I propose "cabody"
Let the discussion begin: "what is a cabody?"
Do you think it is easier to agree what a "cabody" is than to define what a
"planet" is? I think I know the answer.....
Clear skies
Carsten A. Arnholm
http://arnholm.org/
N59.776 E10.457
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Date: 26 Aug 2006 10:29:50
From: Willie R. Meghar
Subject: Re: Of Stars, Pluto and Planetary Classification
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"Carsten A. Arnholm" wrote:
>Do you think it is easier to agree what a "cabody" is than to define what a
>"planet" is? I think I know the answer.....
Yes, because preconceived notions as to the meaning of "cabody" do not
exist.
Willie R. Meghar
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Date: 26 Aug 2006 17:13:35
From: Paul Schlyter
Subject: Re: Of Stars, Pluto and Planetary Classification
|
In article <mnt0f2la6grjq1v7t9i8e7l2n82suaccl0@4ax.com >,
Willie R. Meghar <NoMail@thisaddress.net > wrote:
>"Carsten A. Arnholm" wrote:
>
>>Do you think it is easier to agree what a "cabody" is than to define what a
>>"planet" is? I think I know the answer.....
>
>Yes, because preconceived notions as to the meaning of "cabody" do not
>exist.
Check out: http://home.wi.rr.com/cabodyhf/ca.htm :-)
>Willie R. Meghar
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 27 Aug 2006 00:00:44
From: Carsten A. Arnholm
Subject: Re: Of Stars, Pluto and Planetary Classification
|
Willie R. Meghar wrote:
> "Carsten A. Arnholm" wrote:
>
>> Do you think it is easier to agree what a "cabody" is than to define
>> what a "planet" is? I think I know the answer.....
>
> Yes, because preconceived notions as to the meaning of "cabody" do not
> exist.
It is interesting, because my answer was "no" :-)
If we were to characterise "cabody" from the ground up, using what people
think is science, we will end up in exactly the same problem as with the
"planet" discussion, minus the cultural preconceptions.
My point is that the problems with defining what a "planet" is, is not
limited to preconceived notions.
Clear skies
Carsten A. Arnholm
http://arnholm.org/
N59.776 E10.457
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Date: 27 Aug 2006 02:37:25
From: Wally Wonderful
Subject: Re: Of Stars, Pluto and Planetary Classification
|
AustinMN wrote:
> Willie R. Meghar wrote:
> <snip>
>
> > About Stars:
> >
> > Stars remain stars regardless of where they are. A star in orbit
> > about another star is still a star. This is the case regardless of
> > anything occupying a nearby orbit. This is the case even if other
> > stars occupy the same orbit. Even a star found between two widely
> > separated galaxies would still be a star.
>
> This applies elsewhere. Things are what they are, and only rarely do
> they change what they are because of their location. A watch is a
> watch whether it's on the retailer's shelf, strapped to my wrist, or in
> a thief's pocket. It's a watch wheter or not it has a jeweled
> movement, digital movement (yes, there have been such things), a
> quartz oscillator, or some other mechanism for keeping time. It takes
> very special circumstances for it's location to have an impact. Under
> the wheels of a bus, it stops being a watch and becomes a piece of
> junk, not because of it's location, but because the bus did something
> dramatic to it, changing the nature of what it was.
>
> <snip>
>
> > Pay no special attention to Pluto! Let it fall wherever in (or
> > outside) the definition or classification scheme. Pay no special
> > attention to orbits! (See "About Stars" above.). It's the physical
> > body we're interested in, regardless of where that body might be
> > found. If this means that some planetary satellites are also Planets,
> > then so be it!
> >
> > It's not the job of science to keep the number of planets in our solar
> > system small for easy memorization by school children. It's more
> > important to have definitions and classification schemes that science
> > and astronomy can be proud of.
>
> I think the real problem is trying to put a scientific definition to a
> non-scientific term. Astronomers typically don't use the term
> "shooting star" because it is a non-scientific term. Instead, new
> terms were invented and defined. It makes no sense to try to define
> "shooting star" scientifically because it is such a misleading term.
>
> What's really needed is a new term (or, more likely, a set of new
> terms) to define non-star bodies in space. I think astronomers need to
> stop using the term "planet" exept when dealing with the public. We
> figured out that calling man-made sattelites "moons" was not
> appropriate, perhaps even before there were any.
>
> Maybe it's time to throw out the term "planet" and replace it with a
> new set of terms rather than try to force a scientific definition on a
> term that has long outlived it's scientific usefulness.
>
> Austin
Thast the whole problemo - the term wasnt scientific to begin with, but
cultural! That it can be replaced by a "scientific" schemata is ...........
laughable far beyond the scope of planets nd Plutinos! Its human BS
thats involved here ......... not science or planets.
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Date: 25 Aug 2006 19:13:31
From: Paul Schlyter
Subject: Re: Of Stars, Pluto and Planetary Classification
|
In article <v8eue2105srb6tnj85u50bjit6j9o12rnd@4ax.com >,
Willie R. Meghar <NoMail@thisaddress.net > wrote:
> The IAU has come up with a planetary classification scheme that is
> *not* based solely upon the physical nature of the objects being
> classified. The orbital details of an otherwise qualified body can
> exclude it from the "planet" classification.
That's nothing new! Consider Titan, which is bigger and more massive
than Mercury and has an atmosphere as dense as the Earth's atmosphere.
Yet, it's not a planet, because of its orbital characteristics: it
orbits Saturn, not the Sun.
Based solely of the physical nature of the object itself, Titan would
be an obvious planet. Right?
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 25 Aug 2006 14:13:16
From: Willie R. Meghar
Subject: Re: Of Stars, Pluto and Planetary Classification
|
(Paul Schlyter) wrote:
>That's nothing new! Consider Titan, which is bigger and more massive
>than Mercury and has an atmosphere as dense as the Earth's atmosphere.
>Yet, it's not a planet, because of its orbital characteristics: it
>orbits Saturn, not the Sun.
>
>Based solely of the physical nature of the object itself, Titan would
>be an obvious planet. Right?
Right, unless the limiting mass for a planet is reduced to a level
that would exclude Titan, in which case Mercury would not be a planet
either.
Willie R. Meghar
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Date: 26 Aug 2006 09:43:01
From: Paul Schlyter
Subject: Re: Of Stars, Pluto and Planetary Classification
|
In article <nemue210qsl8dh8us29sm32p0fqe22um3k@4ax.com >,
Willie R. Meghar <NoMail@thisaddress.net > wrote:
> (Paul Schlyter) wrote:
>
>> That's nothing new! Consider Titan, which is bigger and more massive
>> than Mercury and has an atmosphere as dense as the Earth's atmosphere.
>> Yet, it's not a planet, because of its orbital characteristics: it
>> orbits Saturn, not the Sun.
>>
>> Based solely of the physical nature of the object itself, Titan would
>> be an obvious planet. Right?
>
> Right, unless the limiting mass for a planet is reduced to a level
> that would exclude Titan, in which case Mercury would not be a planet
> either.
>
> Willie R. Meghar
I think you mean "increased" rather than "reduced"..... :-)
Anyway, no-one has seriously suggested THAT - right?
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 26 Aug 2006 10:29:38
From: Willie R. Meghar
Subject: Re: Of Stars, Pluto and Planetary Classification
|
pausch@saaf.se (Paul Schlyter) wrote:
>In article <nemue210qsl8dh8us29sm32p0fqe22um3k@4ax.com>,
>Willie R. Meghar <NoMail@thisaddress.net> wrote:
>
>> (Paul Schlyter) wrote:
>>
>>> Based solely of the physical nature of the object itself, Titan would
>>> be an obvious planet. Right?
>>
>> Right, unless the limiting mass for a planet is reduced to a level
>> that would exclude Titan, in which case Mercury would not be a planet
>> either.
>>
>> Willie R. Meghar
>
>I think you mean "increased" rather than "reduced"..... :-)
Some suppositions were required in order to answer your initial
question. I used "reduced" based on the suppositions that mass was
used as "the" physical nature criteria, and there existed some minimum
mass less than or equal to the mass of Mercury that a body must have
in order to be called a planet. Without these suppositions (that I
thought were self-evident) it would not have been possible to answer
your question.
In this context, I believe "reduced" was the correct word to use.
>Anyway, no-one has seriously suggested THAT - right?
If by "THAT" you mean the classification of solar system bodies based
on mass without regard to orbital details, then I reply that my
suggestion that this be done is a serious suggestion; but if by
"serious" you're asking if the IAU has considered it -- I don't know.
Willie R. Meghar
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Date: 26 Aug 2006 17:13:35
From: Paul Schlyter
Subject: Re: Of Stars, Pluto and Planetary Classification
|
In article <tlt0f2l1ju01ums5t9bhc16d7lo2ig6961@4ax.com >,
Willie R. Meghar <NoMail@thisaddress.net > wrote:
>pausch@saaf.se (Paul Schlyter) wrote:
>
>>In article <nemue210qsl8dh8us29sm32p0fqe22um3k@4ax.com>,
>>Willie R. Meghar <NoMail@thisaddress.net> wrote:
>>
>>> (Paul Schlyter) wrote:
>>>
>>>> Based solely of the physical nature of the object itself, Titan would
>>>> be an obvious planet. Right?
>>>
>>> Right, unless the limiting mass for a planet is reduced to a level
>>> that would exclude Titan, in which case Mercury would not be a planet
>>> either.
>>>
>>> Willie R. Meghar
>>
>>I think you mean "increased" rather than "reduced"..... :-)
>
>Some suppositions were required in order to answer your initial
>question. I used "reduced" based on the suppositions that mass was
>used as "the" physical nature criteria, and there existed some minimum
>mass less than or equal to the mass of Mercury that a body must have
>in order to be called a planet. Without these suppositions (that I
>thought were self-evident) it would not have been possible to answer
>your question.
>
>In this context, I believe "reduced" was the correct word to use.
You wrote "limiting mass for a planet is reduced", not "physical nature
criteria for a planet is reduced". Reducing a mass means making it smaller,
not larger. Right?
>>Anyway, no-one has seriously suggested THAT - right?
>
>If by "THAT" you mean the classification of solar system bodies based
>on mass without regard to orbital details,
No ... instead I meant creating a classification such that Mercury too
would have become a non-planet. Increasing the limiting mass sufficiently
could be a way to accomplish that.
>then I reply that my
>suggestion that this be done is a serious suggestion; but if by
>"serious" you're asking if the IAU has considered it -- I don't know.
>
>Willie R. Meghar
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 26 Aug 2006 14:13:31
From: Willie R. Meghar
Subject: Re: Of Stars, Pluto and Planetary Classification
|
(Paul Schlyter) wrote:
>You wrote "limiting mass for a planet is reduced", not "physical nature
>criteria for a planet is reduced". Reducing a mass means making it smaller,
>not larger. Right?
I apologize for the impreciseness of the words I chose to use. From
the above it would seem that you've managed to decipher what I had
meant.
Reducing a mass means making it less massive :-)
>>>Anyway, no-one has seriously suggested THAT - right?
>>
>>If by "THAT" you mean the classification of solar system bodies based
>>on mass without regard to orbital details,
>
>No ... instead I meant creating a classification such that Mercury too
>would have become a non-planet. Increasing the limiting mass sufficiently
>could be a way to accomplish that.
I don't know of that has been seriously suggested by anyone.
Willie R. Meghar
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Date: 26 Aug 2006 06:27:51
From: AustinMN
Subject: Re: Of Stars, Pluto and Planetary Classification
|
Brian Tung wrote:
> AustinMN wrote:
> > What's really needed is a new term (or, more likely, a set of new
> > terms) to define non-star bodies in space. I think astronomers need to
> > stop using the term "planet" exept when dealing with the public.
Then they needed a definition that isn't offensive to the public. The
IAU definition is highly offensive to the public. "Any non-star object
Pluto-sized or larger" would make more sense for that purpose.
Scientifically useless except when deligh with the public.
> I think that is exactly why they wanted a definition--so that when some
> new object was discovered, they would be able to agree on one of the
> following:
>
> "It is a planet."
>
> "It is not a planet."
>
> "We haven't made enough observations of it (and possibly its
> environment) to be sure. When we have, we'll know."
>
> And to avoid either utter disagreement and chaos, or agreement on the
> following non-answer:
>
> "Well, that depends on what you call a planet..."
A perfectly valid answer.
As is "we don't use that term any more."
Austin
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Date: 26 Aug 2006 13:48:47
From: Brian Tung
Subject: Re: Of Stars, Pluto and Planetary Classification
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AustinMN wrote:
> > "Well, that depends on what you call a planet..."
>
> A perfectly valid answer.
Well, yes, *you* see that, and *I* see that, but J Random Guy-on-Street
is impatient with that kind of ambiguity. I suspect that's why the IAU
wanted to avoid that situation.
> As is "we don't use that term any more."
"Yes, but is it a planet?" :-T
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 26 Aug 2006 06:23:01
From: AustinMN
Subject: Re: Of Stars, Pluto and Planetary Classification
|
Carsten A. Arnholm wrote:
> Willie R. Meghar wrote:
> > "AustinMN" wrote:
> >
> >> I think the real problem is trying to put a scientific definition to
> >> a non-scientific term. Astronomers typically don't use the term
> >> "shooting star" because it is a non-scientific term. Instead, new
> >> terms were invented and defined. It makes no sense to try to define
> >> "shooting star" scientifically because it is such a misleading term.
> >>
> >> What's really needed is a new term (or, more likely, a set of new
> >> terms) to define non-star bodies in space. I think astronomers need
> >> to stop using the term "planet" exept when dealing with the public.
> >> We figured out that calling man-made sattelites "moons" was not
> >> appropriate, perhaps even before there were any.
> >>
> >> Maybe it's time to throw out the term "planet" and replace it with a
> >> new set of terms rather than try to force a scientific definition on
> >> a term that has long outlived it's scientific usefulness.
> >
> > Yes, this makes a great deal of sense!
> >
> > Willie R. Meghar
>
> Let us test this. I propose "cabody"
>
> Let the discussion begin: "what is a cabody?"
>
> Do you think it is easier to agree what a "cabody" is than to define what a
> "planet" is? I think I know the answer.....
This is a wrong approach. First you come up with a definition, then
apply a term. That does not mean you can't have a term in mind, but
the truth is, this whole discusion has proven that the term "planet" is
useless.
On the other hand, if you start with "A cabody is any object that has
sufficient mass for its self-gravity to overcome rigid body forces so
that it assumes a hydrostatic equilibrium (nearly round) shape and
would not otherwise be 1) classified as a star or 2) be primarily
composed of a form of matter not naturally occuring on earth" then
everyone knows what that means (assuming we don't need to define
"nearly round," "star," or "earth").
If the definition works, you can then use any appropriate term. Call
it a lubite or glyph or a Taumaugh, as long as we can agree on the
definition, (and is not already in use or would be misleading) it
works. Using a term like "space rock" or "pond water" would not work
because they would, by their nature, be misleading. We will not likely
ever agree on the definition of a "wandering star" or "planet" and the
term will always (OK, perhaps only for a very long time) be interpreted
by the public differently from any scientific definition.
It could then be qualified with other terms - solar cabody, extra-solar
cabody, jovian cabody, kaiper belt cabody, short-period cabody, even
sub-cabody - and everyone in the astro sciences community still knows
what you mean. The definition is based on what the object is, not
where it is (but can be qualified that way) and can be applied
immediately.
The appropriate response to the question "Is it a planet?" is
relatively simple.
"Astronomers can't agree on exactly what a planet is so we just don't
use the term any more."
People will get used to it. There are other commonly used terms that
are no longer used, even by the public, because they had no useful
scientific meaning.
It just doesn't make sense to call them "wandering stars" any more.
Planets are for poets.
Austin
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Date: 26 Aug 2006 23:56:00
From: Carsten A. Arnholm
Subject: Re: Of Stars, Pluto and Planetary Classification
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AustinMN wrote:
> Carsten A. Arnholm wrote:
>> Willie R. Meghar wrote:
>>> "AustinMN" wrote:
>>>
>>>> I think the real problem is trying to put a scientific definition
>>>> to
>>>> a non-scientific term. Astronomers typically don't use the term
>>>> "shooting star" because it is a non-scientific term. Instead, new
>>>> terms were invented and defined. It makes no sense to try to
>>>> define "shooting star" scientifically because it is such a
>>>> misleading term.
>>>>
>>>> What's really needed is a new term (or, more likely, a set of new
>>>> terms) to define non-star bodies in space. I think astronomers
>>>> need
>>>> to stop using the term "planet" exept when dealing with the public.
>>>> We figured out that calling man-made sattelites "moons" was not
>>>> appropriate, perhaps even before there were any.
>>>>
>>>> Maybe it's time to throw out the term "planet" and replace it with
>>>> a new set of terms rather than try to force a scientific
>>>> definition on
>>>> a term that has long outlived it's scientific usefulness.
>>>
>>> Yes, this makes a great deal of sense!
>>>
>>> Willie R. Meghar
>>
>> Let us test this. I propose "cabody"
>>
>> Let the discussion begin: "what is a cabody?"
>>
>> Do you think it is easier to agree what a "cabody" is than to define
>> what a "planet" is? I think I know the answer.....
>
> This is a wrong approach. First you come up with a definition, then
> apply a term. That does not mean you can't have a term in mind, but
> the truth is, this whole discusion has proven that the term "planet"
> is useless.
And I was trying to make the point that coming up with another term is
equally useless. My point is that you cannot scientifically define what a
planet or a "cabody" is, because these terms are just language conventions
anyway. It is like trying to prove scientifically that a day has 24 hours.
> On the other hand, if you start with "A cabody is any object that has
> sufficient mass for its self-gravity to overcome rigid body forces so
> that it assumes a hydrostatic equilibrium (nearly round) shape and
> would not otherwise be 1) classified as a star or 2) be primarily
> composed of a form of matter not naturally occuring on earth" then
> everyone knows what that means (assuming we don't need to define
> "nearly round," "star," or "earth").
I don't think so. You have just replaced "planet" with "cabody". The problem
isn't just that people have sentiments around the word "planet", it is also
that such definitions are intrinsically problematic, no matter which word
you apply it to. This is because nature doesn't create distinct groups of
bodies, there are so many border cases.
> If the definition works, you can then use any appropriate term. Call
> it a lubite or glyph or a Taumaugh, as long as we can agree on the
> definition, (and is not already in use or would be misleading) it
> works.
This is true if it really describes something significant in nature.
However, the IAU definition of "planet" is arbitrary (or chosen to only
mildly interfere with culture) and your definition above is also arbitrary.
It is like a curve fit to an observation, the formula does not mean
anything.
> Using a term like "space rock" or "pond water" would not work
> because they would, by their nature, be misleading. We will not
> likely ever agree on the definition of a "wandering star" or "planet"
> and the term will always (OK, perhaps only for a very long time) be
> interpreted by the public differently from any scientific definition.
In my opinion, you could say that the IAU definition is saved by the
footnote that lists each and every planet that is supposed to match the
definition. This is the only way we can agree which planets exist. The
definition is in my opinion arbitrary non-science, plus it is useless in
practice. How can you determine whether an object is in hydrostatic
equilibrium if you cannot resolve it? And if you can determine it,
hydrostatic equilibrium is just a conventional definition anyway. You might
as well list the 8 planets as they did. Nothing else works.
> It could then be qualified with other terms - solar cabody,
> extra-solar cabody, jovian cabody, kaiper belt cabody, short-period
> cabody, even sub-cabody - and everyone in the astro sciences
> community still knows
> what you mean. The definition is based on what the object is, not
> where it is (but can be qualified that way) and can be applied
> immediately.
The definition of a planet is based on where it is, not what it is. Mercury
is a planet because it orbits the Sun. Titan (bigger than Mercury) is not a
planet because it orbits Saturn. Pluto is not a planet because the IAU said
so :-)
> The appropriate response to the question "Is it a planet?" is
> relatively simple.
>
> "Astronomers can't agree on exactly what a planet is so we just don't
> use the term any more."
Well, that will not work. The IAU definition was explicitly trying to make a
definition that meant something to the outside world. After all, they
represent everyone in these matters, and "planet" is a word that we all use.
If they did what you suggest, decide that "planet" wasn't a useful word and
issued a definition of "cabody" instead, they would be in serious trouble.
> People will get used to it. There are other commonly used terms that
> are no longer used, even by the public, because they had no useful
> scientific meaning.
True. But not every useful word has scientific meaning. My point is that
"planet" is a very useful word, but it cannot be assigned to a scientific
meaning. The word will not go away, and you cannot define it scientifically.
Clear skies
Carsten A. Arnholm
http://arnholm.org/
N59.776 E10.457
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Date: 27 Aug 2006 00:37:46
From:
Subject: Re: Of Stars, Pluto and Planetary Classification
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AustinMN wrote:
snip
>
> Maybe it's time to throw out the term "planet" and replace it with a
> new set of terms rather than try to force a scientific definition on a
> term that has long outlived it's scientific usefulness.
>
> Austin
I wholeheartedly agree. The 8 objects now called "planets" are a mixed
bag of two very distinct types of bodies. The only real difference
between Ceres and the 4 smaller "classical" planets is that it is much
smaller than them. Except for the arbitrary criterion of "clearing its
orbital path" there isn't really much to distinguish it from the rocky
planets.
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