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Main
Date: 26 Sep 2006 13:13:18
From: Magnificent Universe
Subject: Test Your Pluto Knowledge!
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Suppose Pluto had the same orbit around the Sun as Mars. When closest to
Earth, how bright would Pluto be?
A. Pluto would still be so faint that you'd need a telescope to see it.
B. Pluto would be bright enough to see through binoculars, but not with the
naked eye.
C. Pluto would be one of the brightest objects in the sky, outshining every
star except the Sun.
Find out the correct answer at http://KenCroswell.com/PlutoQuestion.html .
Other recent stories:
A star in Eridanus may have escaped from the Pleiades cluster: see
http://KenCroswell.com/GD50.html .
The Horsehead Nebula is rotating: see
http://KenCroswell.com/HorseheadNebulaIsRotating.html .
All articles at http://KenCroswell.com/articles.html .
Correct email: MagnificentUniverse "at" yahoo "dot" com.
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Date: 26 Sep 2006 18:14:55
From: Don't Be Evil
Subject: Re: Test Your Pluto Knowledge!
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Magnificent Universe wrote:
> Suppose Pluto had the same orbit around the Sun as Mars. When closest to
> Earth, how bright would Pluto be?
>
> A. Pluto would still be so faint that you'd need a telescope to see it.
>
> B. Pluto would be bright enough to see through binoculars, but not with the
> naked eye.
>
> C. Pluto would be one of the brightest objects in the sky, outshining every
> star except the Sun.
>
> Find out the correct answer at http://KenCroswell.com/PlutoQuestion.html .
>
> Other recent stories:
>
> A star in Eridanus may have escaped from the Pleiades cluster: see
> http://KenCroswell.com/GD50.html .
>
> The Horsehead Nebula is rotating: see
> http://KenCroswell.com/HorseheadNebulaIsRotating.html .
>
> All articles at http://KenCroswell.com/articles.html .
>
> Correct email: MagnificentUniverse "at" yahoo "dot" com.
If Pluto were in Mars orbit, all that ice would be gone, and Pluto
would be smaller and darker.
Is this an attempt to argue that the IAU got it wrong? Mars doesn't
share space with Neptune, 8000 times Pluto's mass. Nor is it one of
hundreds of similar bodies (KBO's).
You can't base your case on a hypothetical situation. Put Earth's moon
in Mars' orbit and you could make the same argument. If Sedna were in
Mercury's orbit...
Respectfully,
Greg
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Date: 27 Sep 2006 02:45:56
From: Wally
Subject: Re: Test Your Pluto Knowledge!
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Don't Be Evil wrote:
> Magnificent Universe wrote:
> > Suppose Pluto had the same orbit around the Sun as Mars. When closest to
> > Earth, how bright would Pluto be?
> >
> > A. Pluto would still be so faint that you'd need a telescope to see it.
> >
> > B. Pluto would be bright enough to see through binoculars, but not with the
> > naked eye.
> >
> > C. Pluto would be one of the brightest objects in the sky, outshining every
> > star except the Sun.
> >
> > Find out the correct answer at http://KenCroswell.com/PlutoQuestion.html .
> >
> > Other recent stories:
> >
> > A star in Eridanus may have escaped from the Pleiades cluster: see
> > http://KenCroswell.com/GD50.html .
> >
> > The Horsehead Nebula is rotating: see
> > http://KenCroswell.com/HorseheadNebulaIsRotating.html .
> >
> > All articles at http://KenCroswell.com/articles.html .
> >
> > Correct email: MagnificentUniverse "at" yahoo "dot" com.
>
> If Pluto were in Mars orbit, all that ice would be gone, and Pluto
> would be smaller and darker.
>
> Is this an attempt to argue that the IAU got it wrong? Mars doesn't
> share space with Neptune, 8000 times Pluto's mass. Nor is it one of
> hundreds of similar bodies (KBO's).
>
> You can't base your case on a hypothetical situation. Put Earth's moon
> in Mars' orbit and you could make the same argument. If Sedna were in
> Mercury's orbit...
>
If Earth were in Sedna's orbit and you were in Spain which would be called
27435t0rr in Springtime ?
>
> Respectfully,
> Greg
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Date: 29 Sep 2006 05:37:57
From: Dan Krueger
Subject: Re: Test Your Pluto Knowledge!
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> If Pluto were in Mars orbit, all that ice would be gone, and Pluto
> would be smaller and darker.
> Is this an attempt to argue that the IAU got it wrong? Mars doesn't
> share space with Neptune, 8000 times Pluto's mass. Nor is it one of
> hundreds of similar bodies (KBO's).
> You can't base your case on a hypothetical situation. Put Earth's moon
> in Mars' orbit and you could make the same argument. If Sedna were in
> Mercury's orbit...
Has anybody evaluated post LASIK vision ? Tell us which ones
you've tried and discounted and we'll find out if the victims
share something in common. THEY DO. LaFitte's men were slavers.
The cultists were murdered by Johansen et al.
The point was also loaded with interior fat, which I wouldn't
have minded so much if they had not, virgin humans are a bitch
to find. James E. Klein Engineering Engineering is the home of
the KDP-2 Optical Design Program for Windows and (soon) MAC OSX
Free KDP-2 (DEMO) ! (Voice and Fax) -----BEGIN PGP SIGNED
MESSAGE----- WHILE IT'S EASY to pick on a group who insist that
they have taken away all references to their phone number or
address, which does not inspire confidence. My impression is
that if Lovecraft had been told that people would still be so
faint that you'd need a telescope to see it.
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Date: 26 Sep 2006 21:55:12
From: Sorcerer
Subject: Re: Test Your Pluto Knowledge!
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"Magnificent Universe" <MagnificentUniverse@yyyyy.com > wrote in message
news:45198a04$0$34541$742ec2ed@news.sonic.net...
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Date: 26 Sep 2006 22:06:13
From:
Subject: Re: Test Your Pluto Knowledge!
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Sorcerer writes:
> Magnificent Universe wrote:
>> Suppose Pluto had the same orbit around the Sun as Mars. When closest to
>> Earth, how bright would Pluto be?
>>
>> A. Pluto would still be so faint that you'd need a telescope to see it.
>>
>> B. Pluto would be bright enough to see through binoculars, but not with the
>> naked eye.
>>
>> C. Pluto would be one of the brightest objects in the sky, outshining every
>> star except the Sun.
>>
>> Find out the correct answer at http://KenCroswell.com/PlutoQuestion.html .
> The idiot doesn't mention albedo once.
You're erroneously presupposing that he's an idiot. Why should he
mention albedo?
> Who is the nutter, you?
What does your question have to do with astronomy, Sorcerer?
> [rest of crap snipped]
On what basis do you call it crap?
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Date: 27 Sep 2006 00:25:34
From: Sorcerer
Subject: Re: Test Your Pluto Knowledge!
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<tholen@antispam.ham > wrote in message
news:pvhSg.7656$%i.3352@tornado.socal.rr.com...
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Date: 27 Sep 2006 00:58:16
From:
Subject: Re: Test Your Pluto Knowledge!
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Sorcerer writes:
>>> Magnificent Universe wrote:
>>>> Suppose Pluto had the same orbit around the Sun as Mars. When closest to
>>>> Earth, how bright would Pluto be?
>>>>
>>>> A. Pluto would still be so faint that you'd need a telescope to see it.
>>>>
>>>> B. Pluto would be bright enough to see through binoculars, but not with the
>>>> naked eye.
>>>>
>>>> C. Pluto would be one of the brightest objects in the sky, outshining every
>>>> star except the Sun.
>>>>
>>>> Find out the correct answer at http://KenCroswell.com/PlutoQuestion.html .
>>> The idiot doesn't mention albedo once.
>> You're erroneously presupposing that he's an idiot. Why should he
>> mention albedo?
> Crosswell's not teaching, but trying.
Non sequitur. I asked why he should mention albedo, not about whether
he's trying to teach or not.
> It is not a presupposition
Classic unsubstantiated and erroneous claim.
> but a post observation.
Your so-called "post observation" is incorrect, Sorcerer. He's not an
idiot. Yet you erroneously presupposed that condition in order to write
your sentence. That's why it's called a presupposition.
> Albedo is essential to his argument,
Classic unsubstantiated and erroneous claim.
> Pluto is observed by reflected sunlight.
So is Mars. So what? The apparent brightness of an object in the
sky is a combination of distance, phase angle, size, and albedo.
He didn't mention size or phase angle either, Sorcerer. Only distance
was mentioned, and indirectly at that.
>>> Who is the nutter, you?
>> What does your question have to do with astronomy, Sorcerer?
> My question was directed at "Magnificent Universe".
Irrelevant, given that I never claimed otherwise, Sorcerer. My
question of you still stands:
What does your question [of Magnificent Universe] have to do with
astronomy, Sorcerer?
> "Suppose Pluto had the same orbit around the Sun as Mars. " has no
> foundation in astronomy.
Pluto, Mars, the Sun, and orbits around the Sun are all astronomical
concepts, Sorcerer. It's perfectly acceptable to hypothesize all
sort of non-existent scenarios. The whole concept of absolute
magnitude within the Solar System is based on an impossible geometric
condition.
> Unless you are he,
Illogical.
> fuck off.
Such foul language.
>>> [rest of crap snipped]
>> On what basis do you call it crap?
> Crap, drool, drivel, I don't care what it is called,
Non sequitur. I asked for your basis for calling it crap, Sorcerer,
not for synonyms.
> fuckwit,
Who is "fuckwit", Sorcerer? Still suffering from attribution problems?
> Pluto is where it is
Not in the given scenario, Sorcerer.
> and "what if" or "suppose" has no bearing on it.
Classic unsubstantiated and erroneous claim. The "what if" or "suppose"
has everything to do with the answer. Or do you wish to claim that the
Sun cannot have an absolute magnitude, because it is where it is and
cannot be 10 parsecs away, Sorcerer?
> Androcles.
Non sequitur.
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Date: 28 Sep 2006 16:27:04
From: Dan Krueger
Subject: Re: Test Your Pluto Knowledge!
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> "Magnificent Universe" <MagnificentUniverse@yyyyy.com> wrote in message
> news:45198a04$0$34541$742ec2ed@news.sonic.net...
>
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Date: 26 Sep 2006 21:18:00
From:
Subject: Re: Test Your Pluto Knowledge!
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Magnificent Universe writes:
> Suppose Pluto had the same orbit around the Sun as Mars. When closest to
> Earth, how bright would Pluto be?
>
> A. Pluto would still be so faint that you'd need a telescope to see it.
>
> B. Pluto would be bright enough to see through binoculars, but not with the
> naked eye.
>
> C. Pluto would be one of the brightest objects in the sky, outshining every
> star except the Sun.
Simple: C.
Pluto's absolute magnitude is only 0.7 mag fainter than Mars' absolute
magnitude, so Pluto would be only 0.7 mag fainter than Mars when in the
same location in the Solar System. During Mars' perihelic opposition
three years ago, it reached an apparent magnitude of -2.9, so Pluto
would be -2.2, brighter than Sirius (about twice as bright).
So?
By the way, the Sun isn't a star: it's a dwarf star. It's the new
IAU nomenclature; a dwarf something is no longer a something. I
wonder when the AKC will declare that toy poodles are no longer
poodles?
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Date: 26 Sep 2006 22:02:18
From: Alan French
Subject: Re: Test Your Pluto Knowledge!
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<tholen@antispam.ham > wrote in message
news:cOgSg.9260$xg7.1622@tornado.socal.rr.com...
> By the way, the Sun isn't a star: it's a dwarf star. It's the new
> IAU nomenclature; a dwarf something is no longer a something. I
> wonder when the AKC will declare that toy poodles are no longer
> poodles?
The way I understand it is that a dwarf star is still a star, and a dwarf
galaxy is still a galaxy, but a dwarf planet is not a planet. (We do know
that toy poodles are too small to be raal dogs - real dogs go WOOF, not
yap-yap-yap. <G >)
Clear skies, Alan
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Date: 26 Sep 2006 21:57:54
From: Sorcerer
Subject: Re: Test Your Pluto Knowledge!
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<tholen@antispam.ham > wrote in message
news:cOgSg.9260$xg7.1622@tornado.socal.rr.com...
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Date: 26 Sep 2006 22:07:24
From:
Subject: Re: Test Your Pluto Knowledge!
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Sorcerer writes:
>> Magnificent Universe writes:
>>> Suppose Pluto had the same orbit around the Sun as Mars. When closest to
>>> Earth, how bright would Pluto be?
>>>
>>> A. Pluto would still be so faint that you'd need a telescope to see it.
>>>
>>> B. Pluto would be bright enough to see through binoculars, but not with the
>>> naked eye.
>>>
>>> C. Pluto would be one of the brightest objects in the sky, outshining every
>>> star except the Sun.
>> Simple: C.
>>
>> Pluto's absolute magnitude is only 0.7 mag fainter than Mars' absolute
>> magnitude, so Pluto would be only 0.7 mag fainter than Mars when in the
>> same location in the Solar System. During Mars' perihelic opposition
>> three years ago, it reached an apparent magnitude of -2.9, so Pluto
>> would be -2.2, brighter than Sirius (about twice as bright).
>>
>> So?
>>
>> By the way, the Sun isn't a star: it's a dwarf star. It's the new
>> IAU nomenclature; a dwarf something is no longer a something. I
>> wonder when the AKC will declare that toy poodles are no longer
>> poodles?
> When puddles are dorsets, of course. Poole is in Dorset.
Non sequitur. I said nothing about puddles, dorsets, or Poole.
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Date: 27 Sep 2006 00:19:53
From: Sorcerer
Subject: Re: Test Your Pluto Knowledge!
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<tholen@antispam.ham > wrote in message
news:wwhSg.7657$%i.5118@tornado.socal.rr.com...
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Date: 27 Sep 2006 00:45:49
From:
Subject: Re: Test Your Pluto Knowledge!
|
Sorcerer writes:
>>>> Magnificent Universe writes:
>>>>> Suppose Pluto had the same orbit around the Sun as Mars. When closest to
>>>>> Earth, how bright would Pluto be?
>>>>>
>>>>> A. Pluto would still be so faint that you'd need a telescope to see it.
>>>>>
>>>>> B. Pluto would be bright enough to see through binoculars, but not with the
>>>>> naked eye.
>>>>>
>>>>> C. Pluto would be one of the brightest objects in the sky, outshining every
>>>>> star except the Sun.
>>>> Simple: C.
>>>>
>>>> Pluto's absolute magnitude is only 0.7 mag fainter than Mars' absolute
>>>> magnitude, so Pluto would be only 0.7 mag fainter than Mars when in the
>>>> same location in the Solar System. During Mars' perihelic opposition
>>>> three years ago, it reached an apparent magnitude of -2.9, so Pluto
>>>> would be -2.2, brighter than Sirius (about twice as bright).
>>>>
>>>> So?
>>>>
>>>> By the way, the Sun isn't a star: it's a dwarf star. It's the new
>>>> IAU nomenclature; a dwarf something is no longer a something. I
>>>> wonder when the AKC will declare that toy poodles are no longer
>>>> poodles?
>>> When puddles are dorsets, of course. Poole is in Dorset.
>> Non sequitur.
> Of course it is.
Glad you agree.
> So are toy poodles and the American Kennel Club,
Incorrect; sorry that you are unable to see the connection, Sorcerer.
> fuckwit.
Who is "fuckwit", Sorcerer? Suffering from attribution problems?
> If you wish to have a joke don't whine when it comes back to you.
The key word here is "if". No joke was involved on my part, Sorcerer.
>> I said nothing about puddles, dorsets, or Poole.
> Non sequitur.
Classic unsubstantiated and erroneous claim.
> Androcles.
Non sequitur.
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Date: 27 Sep 2006 02:40:37
From: Wally
Subject: Re: Test Your Pluto Knowledge!
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Sorcerer wrote:
> <tholen@antispam.ham> wrote in message
> news:wwhSg.7657$%i.5118@tornado.socal.rr.com...
>
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Date: 27 Sep 2006 07:42:41
From: Paul Schlyter
Subject: Re: Test Your Pluto Knowledge!
|
In article <45198a04$0$34541$742ec2ed@news.sonic.net >,
Magnificent Universe <MagnificentUniverse@yyyyy.com > wrote:
> Suppose Pluto had the same orbit around the Sun as Mars. When closest to
> Earth, how bright would Pluto be?
>
> A. Pluto would still be so faint that you'd need a telescope to see it.
>
> B. Pluto would be bright enough to see through binoculars, but not with the
> naked eye.
>
> C. Pluto would be one of the brightest objects in the sky, outshining every
> star except the Sun.
>
> Find out the correct answer at http://KenCroswell.com/PlutoQuestion.html
Ken Crosswell's "correct" answer to this question is:
-------------------------------------------------------------------------------
C. Pluto would be one of the brightest objects in the sky, outshining every star
except the Sun.
.....................
But if Pluto were closer to us--as close as Mars, for example--it would be
incredibly bright, ancient people would have recognized it as a planet long ago,
and modern people probably wouldn't be debating its planethood!
-------------------------------------------------------------------------------
Ken Crosswell needs to learn some physics !!!
Superficially, he's right: Pluto's absolute magnitude is -1.0 and
Mars' absolute magnitude is -1.51. Therefore, if Pluto was as close
as Mars, it would shine 0.5 magnitudes fainter than Mars. When
closest, Mars shines at mag -2.8 which would mean Pluto would shine at
mag -2.3 if it was as close as Mars.
However, the albedo of Pluto is very high - some 95%. This is because
Pluto is convered with deep frozen ices which are very bright. If we
put Pluto at Mars' distance, these ices would most likely melt away,
and Pluto's albedo would become much lower. Since Pluto is very
small, it wouldn't be able to hold any atmosphere which could have
clouds making the albedo higher (such as for Venus and, to a lesser
extent, the Earth). What the albedo of Pluto then would be is of
course hard to tell - perhaps 15% as for Mars? Or 7% as for the Moon
and Mercury? Let's say 10%.
So if Pluto would be as close as Mars, and its albedo would have been
lowered to 10% after the Sun had melted all those ices away, then
Pluto would shine at around magnitude 0 when as close to the Earth as
Mars is when closest - it would then shone as bright as Vega or
Arcturus. Pluto wouldn't be that close all the time though. Most of
the time, Mars shines approximately around magnitude +1 - if Pluto
followed Mars orbit, then Pluto would shine around magnitude +3.5 most
of the time. That would make Pluto a naked-eye object, although one
would need to know the sky to distinguish Pluto from many stars with a
similar brightness.
If Ceres or Vesta followed Mars' orbit, they would shine around
magnitude 4 to 5 most of the time, brightening to magnitude +1 when
closest to the Earth.
Ken Crosswell also writes:
# ancient people would have recognized it as a planet long ago, and
# modern people probably wouldn't be debating its planethood!
Perhaps it's best to refrain from speculating how people would act
in a different world.... :-)
The planethood debate about (134340) Pluto is only temporary - just
like the planethood debate of (1) Ceres, (2) Pallas, (3) Juno and (4)
Vesta was temporary some 150 years ago.
One interesting thing to note: if Pluto and Mars really were
co-orbital, then according to the current IAU definition of "planet",
neither would be a planet. Both would be dwarf planets, since neither
would have "cleared the neighbourhood" of their common orbit.
--
----------------------------------------------------------------
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 Sep 2006 11:57:26
From:
Subject: Re: Test Your Pluto Knowledge!
|
Paul Schlyter writes:
> Magnificent Universe wrote:
>> Suppose Pluto had the same orbit around the Sun as Mars. When closest to
>> Earth, how bright would Pluto be?
>>
>> A. Pluto would still be so faint that you'd need a telescope to see it.
>>
>> B. Pluto would be bright enough to see through binoculars, but not with the
>> naked eye.
>>
>> C. Pluto would be one of the brightest objects in the sky, outshining every
>> star except the Sun.
>>
>> Find out the correct answer at http://KenCroswell.com/PlutoQuestion.html
> Ken Crosswell's "correct" answer to this question is:
>
> -------------------------------------------------------------------------------
> C. Pluto would be one of the brightest objects in the sky, outshining every star
> except the Sun.
> ......................
> But if Pluto were closer to us--as close as Mars, for example--it would be
> incredibly bright, ancient people would have recognized it as a planet long ago,
> and modern people probably wouldn't be debating its planethood!
> -------------------------------------------------------------------------------
>
> Ken Crosswell needs to learn some physics !!!
He already learned the inverse square law, which is what his question
is all about.
> Superficially, he's right: Pluto's absolute magnitude is -1.0
Pluto's absolute magnitude is -0.81.
> and Mars' absolute magnitude is -1.51. Therefore, if Pluto was as close
> as Mars, it would shine 0.5 magnitudes fainter than Mars. When
> closest, Mars shines at mag -2.8 which would mean Pluto would shine at
> mag -2.3 if it was as close as Mars.
>
> However, the albedo of Pluto is very high - some 95%.
Balderdash. You "need to learn some physics". Take the diameter of
2300 km, the absolute magnitude of -0.81, and work out the mean
albedo. It's not anywhere close to 95 percent.
> This is because
> Pluto is convered with deep frozen ices which are very bright. If we
> put Pluto at Mars' distance, these ices would most likely melt away,
> and Pluto's albedo would become much lower. Since Pluto is very
> small, it wouldn't be able to hold any atmosphere
Then explain why it has an atmosphere.
> The planethood debate about (134340) Pluto is only temporary - just
> like the planethood debate of (1) Ceres, (2) Pallas, (3) Juno and (4)
> Vesta was temporary some 150 years ago.
Incorrect; those four asteroids have been planets since their
discovery: minor planets, but planets nonetheless. Only in
August did the IAU decide to do away with "minor planet" in the
new nomenclature. Ceres is a dwarf planet, which ought to be a
planet as much as s dwarf star (like the Sun) is a star and a
dwarf galaxy is a galaxy.
But the debate is far from over.
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Date: 27 Sep 2006 20:07:05
From:
Subject: Re: Test Your Pluto Knowledge!
|
Paul Schlyter wrote, in part:
> Ken Crosswell's "correct" answer to this question is:
>
> -------------------------------------------------------------------------------
> C. Pluto would be one of the brightest objects in the sky, outshining every star
> except the Sun.
> .....................
> But if Pluto were closer to us--as close as Mars, for example--it would be
> incredibly bright, ancient people would have recognized it as a planet long ago,
> and modern people probably wouldn't be debating its planethood!
> -------------------------------------------------------------------------------
>
> Ken Crosswell needs to learn some physics !!!
>
> Superficially, he's right: Pluto's absolute magnitude is -1.0 and
> Mars' absolute magnitude is -1.51. Therefore, if Pluto was as close
> as Mars, it would shine 0.5 magnitudes fainter than Mars. When
> closest, Mars shines at mag -2.8 which would mean Pluto would shine at
> mag -2.3 if it was as close as Mars.
And that, of course, comes as a surprise. After all, Pluto is much
*smaller* than Mars, or even Mercury. Hence, we would have expected it
to be a dim planet.
> However, the albedo of Pluto is very high - some 95%. This is because
> Pluto is convered with deep frozen ices which are very bright. If we
> put Pluto at Mars' distance, these ices would most likely melt away,
> and Pluto's albedo would become much lower. Since Pluto is very
> small, it wouldn't be able to hold any atmosphere which could have
> clouds making the albedo higher (such as for Venus and, to a lesser
> extent, the Earth). What the albedo of Pluto then would be is of
> course hard to tell - perhaps 15% as for Mars? Or 7% as for the Moon
> and Mercury? Let's say 10%.
>
> So if Pluto would be as close as Mars, and its albedo would have been
> lowered to 10% after the Sun had melted all those ices away, then
> Pluto would shine at around magnitude 0 when as close to the Earth as
> Mars is when closest - it would then shone as bright as Vega or
> Arcturus. Pluto wouldn't be that close all the time though. Most of
> the time, Mars shines approximately around magnitude +1 - if Pluto
> followed Mars orbit, then Pluto would shine around magnitude +3.5 most
> of the time. That would make Pluto a naked-eye object, although one
> would need to know the sky to distinguish Pluto from many stars with a
> similar brightness.
>
> If Ceres or Vesta followed Mars' orbit, they would shine around
> magnitude 4 to 5 most of the time, brightening to magnitude +1 when
> closest to the Earth.
> The planethood debate about (134340) Pluto is only temporary - just
> like the planethood debate of (1) Ceres, (2) Pallas, (3) Juno and (4)
> Vesta was temporary some 150 years ago.
Speaking about Ceres, Pallas, Juno, and Vesta... which one of them is
not like the others?
The answer is Juno: Ceres is the largest asteroid, and Pallas and Vesta
are the next two largest... but Juno is smaller than several other
asteroids besides those three. However, it happens to be unusually
bright for its size.
I really don't think that *albedo* is a very good characteristic to
include in the definition of a planet. Yet, the fact that objects more
readily seen are also more likely to be accepted as important does mean
that he *has* raised an interesting, and unusual, argument in the
Pluto-as-planet debate.
John Savard
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Date: 28 Sep 2006 07:13:09
From: Paul Schlyter
Subject: Re: Test Your Pluto Knowledge!
|
In article <1159412825.476115.155070@m7g2000cwm.googlegroups.com >,
<jsavard@ecn.ab.ca > wrote:
> Paul Schlyter wrote, in part:
>> Ken Crosswell's "correct" answer to this question is:
>>
>> -------------------------------------------------------------------------------
>> C. Pluto would be one of the brightest objects in the sky, outshining every star
>> except the Sun.
>> .....................
>> But if Pluto were closer to us--as close as Mars, for example--it would be
>> incredibly bright, ancient people would have recognized it as a planet long ago,
>> and modern people probably wouldn't be debating its planethood!
>> -------------------------------------------------------------------------------
>>
>> Ken Crosswell needs to learn some physics !!!
>>
>> Superficially, he's right: Pluto's absolute magnitude is -1.0 and
>> Mars' absolute magnitude is -1.51. Therefore, if Pluto was as close
>> as Mars, it would shine 0.5 magnitudes fainter than Mars. When
>> closest, Mars shines at mag -2.8 which would mean Pluto would shine at
>> mag -2.3 if it was as close as Mars.
>
> And that, of course, comes as a surprise. After all, Pluto is much
> *smaller* than Mars, or even Mercury. Hence, we would have expected it
> to be a dim planet.
The reference I used for the figures above - Allen's "Astrophysical
Quantities" from 1973 - did put Pluto's diameter as approximately the same
as Mars - somewhat smaller but not much. But in 1973 Charon hadn't been
discovered so we didn't know Pluto's acutal size yet. That book also
put Pluto's albedo as somewhat lower than Mars' albedo - since Pluto is
much smaller than Allen said it was in 1973, its albedo is also much
higher:
>> However, the albedo of Pluto is very high - some 95%.
....but not quite that high though - "only" some 60%. And Allen
1973 also seemed to overestimate the absolute magnitude of Pluto
a little - more modern soruces give -0.8 or -0.9 instead.
>> This is because
>> Pluto is convered with deep frozen ices which are very bright. If we
>> put Pluto at Mars' distance, these ices would most likely melt away,
>> and Pluto's albedo would become much lower. Since Pluto is very
>> small, it wouldn't be able to hold any atmosphere which could have
>> clouds making the albedo higher (such as for Venus and, to a lesser
>> extent, the Earth). What the albedo of Pluto then would be is of
>> course hard to tell - perhaps 15% as for Mars? Or 7% as for the Moon
>> and Mercury? Let's say 10%.
>>
>> So if Pluto would be as close as Mars, and its albedo would have been
>> lowered to 10% after the Sun had melted all those ices away, then
>> Pluto would shine at around magnitude 0 when as close to the Earth as
>> Mars is when closest - it would then shone as bright as Vega or
>> Arcturus. Pluto wouldn't be that close all the time though. Most of
>> the time, Mars shines approximately around magnitude +1 - if Pluto
>> followed Mars orbit, then Pluto would shine around magnitude +3.5 most
>> of the time. That would make Pluto a naked-eye object, although one
>> would need to know the sky to distinguish Pluto from many stars with a
>> similar brightness.
>>
>> If Ceres or Vesta followed Mars' orbit, they would shine around
>> magnitude 4 to 5 most of the time, brightening to magnitude +1 when
>> closest to the Earth.
>
>> The planethood debate about (134340) Pluto is only temporary - just
>> like the planethood debate of (1) Ceres, (2) Pallas, (3) Juno and (4)
>> Vesta was temporary some 150 years ago.
>
> Speaking about Ceres, Pallas, Juno, and Vesta... which one of them is
> not like the others?
>
> The answer is Juno: Ceres is the largest asteroid, and Pallas and Vesta
> are the next two largest... but Juno is smaller than several other
> asteroids besides those three. However, it happens to be unusually
> bright for its size.
>
> I really don't think that *albedo* is a very good characteristic to
> include in the definition of a planet. Yet, the fact that objects more
> readily seen are also more likely to be accepted as important does mean
> that he *has* raised an interesting, and unusual, argument in the
> Pluto-as-planet debate.
Perhaps we should, besides "dwarf planet", also define "dark planet":
a "dark planet" is not a planet because its albedo is too low..... :-)
> John Savard
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