Pluto is out from planet dictionary

In sci.astro George Dishman wrote:


In sci.astro Lora Crighton wrote:

If you call it a planet, a dwarf planet, or something else doesn't really
make a
different - it's still just as fascinating.

I think Lora's view is by far the most sensible. We
aren't going to tell New Horizons to come back!

Agreed, Lora and George!

Actually it is a question of language and I think this
is precisely what the pro-planet lobby were trying to
achieve is proposal 5B, to reinstate Pluto by the back
door by creating a subtype by the addition of the word
"classical" to the definition of "planet". We should
note that this was specifically rejected by the vote so,
as you correctly note below, the current IAU definition
does not includes sub-types of "planet" but provides two
mutually exclusive groups called "planets" and "dwarf
planets".

We see this very much the same way, and your outstanding
Web page mentioned below very nicely sums up the logic.

A curious question: Why did the supporters of 5B choose
"classical planet" rather than "major planet"? The latter
term seems to me much more familiar, comprehensible, and
pertinent to the issue of dynamical dominance.

Certainly people will continue to describe Pluto in
the way they want, and to a high degree the definition
of language springs from common usage. In that sense
the definition decreed by the IAU may in the end turn
out to be academic. It will be interesting to see how
quickly any major dictionaries revise their entries.

Yes, and I would give the IAU credit for nicely identifying
most of the main relevant distinctions if one is seeking
reasonably consistent definitions.

That is the option presented in Resolution 5B with your
choice of "major" replacing the proposed "classical".
That proposal was not carried hence as you make clear
next, the IAU definition now recognises on those you
describe as "orbit-clearing" as true planets.

Exactly: "planet" in 5A equals "major planet" in a usage
like that of 5B.

Another way of putting this is that in 5A, "planet" might
be said to have a specific meaning: a traditionnal "major
planet" that has cleared its orbit. In 5B or my variant,
"planet" has a generic meaning embracing two species,
"major planet" (orbit-clearing) and "dwarf planet" (not
orbit-clearing).

I suspect this question may crop up regularly in the
future so I have written a brief page to avoid having
to repeat my views. It is a bit rough at the moment and
not checked so may have some errors. Comments welcome.

http://www.georgedishman.f2s.com/astronomy/planet.html

Thank you for an excellent presentation! You combine the
actual resolutions with a step-by-step commentary making
the texts and the logic of their interpretation very
conveniently accessible.

Of course, I could proofread more closely -- but it's a
fine explanation, and may incidentally help to correct
the understanding which some people might still have
that 5B passed. What I'd guess is that people saw an
IAU Web page of _pending_ resolutions posted prior
to the vote, including 5B, and get the impression
that "classical planet" was actually adopted. Your
page makes it clear that 5B was, of course, defeated,
and draws from that the logical conclusions.

The one thing that might be added -- especially if
you or others can improve on my first quick attempt --
is a set of diagrams to show visually the levels of
definition we're discussing. Here's that crude first
try; note, by the way, that after the diagrams of
5A and 5B, there's a diagram for the kind of compromise
I've proposed, where the term "planet" actually appears
twice, once in a generic meaning (like the defeated 5B)
and once in a specific meaning (like the adopted 5A),
allowing a choice between the two usages.

[composed with monospaced font]

-----------------------
Resolution 5A (Adopted)
-----------------------

------------------ Solar system bodies -----------------
| | |
Hydrostatic equilibrium, Not enough mass for Satellite
self-gravity produces hydrostatic equilibrium; of another
"nearly round" shape; and not a satellite of another body [other
not a satellite of another body [other than Sun] than Sun]
body [other than Sun] | |
| | |
| | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
Planet Dwarf Planet Small Solar System Body Satellite
(clears (doesn't (e.g. most Solar System (e.g. Moon,
orbit) clear orbit) asteroids, TNOs, comets) Titan)

TNO = "Trans-Neptunian Object"


------------------------
Resolution 5B (defeated)
------------------------

------------------ Solar system bodies -----------------
| | |
Hydrostatic equilibrium, Not enough mass for Satellite
self-gravity produces hydrostatic equilibrium; of another
"nearly round" shape; and not a satellite of another body [other
not a satellite of another body [other than Sun] than Sun]
body [other than Sun] | |
| | |
| | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
Classical Dwarf Small Solar System Body Satellite
Planet Planet (e.g. most Solar System (e.g. Moon,
(clears orbit) (doesn't asteroids, TNOs, comets) Titan)
clear orbit)



--------------------------------
Possible compromise proposal
for future consideration
--------------------------------

------------------- Solar system bodies ----------------
| | |
Hydrostatic equilibrium, Not enough mass for Satellite
self-gravity produces hydrostatic equilibrium; of another
"nearly round" shape; and not a satellite of another body [other
not a satellite of another body [other than Sun] than Sun]
body [other than Sun] | |
| | |
Planet in broad sense | |
| | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
Major Dwarf Small Solar System Body Satellite
Planet Planet (e.g. most Solar System (e.g. Moon,
or (doesn't asteroids, TNOs, comets) Titan)
Planet clear
in strict orbit)
sense
(clears orbit)

Again, I'm not sure how clear these diagrams are, or how they might be
improved -- but your page is a very handy explanation of the vote.

Most appreciatively,

Margo Schulter

"Margo Schulter" wrote in message
...
In sci.astro George Dishman wrote:

much trimmed as we seem to be in agreement

We see this very much the same way, and your outstanding
Web page mentioned below very nicely sums up the logic.

Thanks.

A curious question: Why did the supporters of 5B choose
"classical planet" rather than "major planet"? The latter
term seems to me much more familiar, comprehensible, and
pertinent to the issue of dynamical dominance.

Beats me. It made "classical" the antonym of "dwarf",
great for Trivial Pursuit but rather odd by any other
standard.

snip

Another way of putting this is that in 5A, "planet" might
be said to have a specific meaning: a traditionnal "major
planet" that has cleared its orbit. In 5B or my variant,
"planet" has a generic meaning embracing two species,
"major planet" (orbit-clearing) and "dwarf planet" (not
orbit-clearing).

Indeed, though I think that opens up the original problem
of producing thousands of planets most of which are too
small to deserve that name given the traditional meaning
of the word.

Incidentally this page gives an interesting history of
the use of "asteroid" versus "minor planet"

http://aa.usno.navy.mil/hilton/Aster...orplanets.html

I think the public view might be that Ceres and the larger
bodies might be justifiably called "minor planets" while
the word "asteroid" is more apt for assorted small rubble.

I suspect this question may crop up regularly in the
future so I have written a brief page to avoid having
to repeat my views. It is a bit rough at the moment and
not checked so may have some errors. Comments welcome.

http://www.georgedishman.f2s.com/astronomy/planet.html

Thank you for an excellent presentation! You combine the
actual resolutions with a step-by-step commentary making
the texts and the logic of their interpretation very
conveniently accessible.

Thanks.

Of course, I could proofread more closely

I am hoping to be more accurate in some of the grammatical
terms I am using but that's less important than getting the
understanding across.

-- but it's a
fine explanation, and may incidentally help to correct
the understanding which some people might still have
that 5B passed. What I'd guess is that people saw an
IAU Web page of _pending_ resolutions posted prior
to the vote, including 5B, and get the impression
that "classical planet" was actually adopted. Your
page makes it clear that 5B was, of course, defeated,
and draws from that the logical conclusions.

Actually I was one of those people until someone
mentioned the result. The IAU web site doesn't actually
highlight the vote results on their home page ... hold
the phone, yes it does now. There is now a link which
wasn't there when I went out a few hours ago. I haven't
had a chance to check in detail but the formal page
looks the same as 5A at first glance.

The one thing that might be added -- especially if
you or others can improve on my first quick attempt --
is a set of diagrams to show visually the levels of
definition we're discussing. Here's that crude first
try; note, by the way, that after the diagrams of
5A and 5B, there's a diagram for the kind of compromise
I've proposed, where the term "planet" actually appears
twice, once in a generic meaning (like the defeated 5B)
and once in a specific meaning (like the adopted 5A),
allowing a choice between the two usages.

[composed with monospaced font]

Excellent stuff Margo. I think this might best be laid out
as a flowchart. I had thought of producing a Venn diagram
but that approach isn't so effective. I had some trouble
with satellite as well because "is not a satellite" is not
a requirement for a planet. Perhaps that was left over from
when they were considering Pluto and Charon to be a double
system. Anyway it moves the test to another point in your
chart though I'm not sure where yet. Also the start point
should be "celestial body" rather than "Solar system bodies".
I'll have to look at this in more detail but if you don't
mind I'll add something like it to the web page.

-----------------------
Resolution 5A (Adopted)
-----------------------

------------------ Solar system bodies -----------------
| | |
Hydrostatic equilibrium, Not enough mass for Satellite
self-gravity produces hydrostatic equilibrium; of another
"nearly round" shape; and not a satellite of another body [other
not a satellite of another body [other than Sun] than Sun]
body [other than Sun] | |
| | |
| | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
Planet Dwarf Planet Small Solar System Body Satellite
(clears (doesn't (e.g. most Solar System (e.g. Moon,
orbit) clear orbit) asteroids, TNOs, comets) Titan)

TNO = "Trans-Neptunian Object"


------------------------
Resolution 5B (defeated)
------------------------

------------------ Solar system bodies -----------------
| | |
Hydrostatic equilibrium, Not enough mass for Satellite
self-gravity produces hydrostatic equilibrium; of another
"nearly round" shape; and not a satellite of another body [other
not a satellite of another body [other than Sun] than Sun]
body [other than Sun] | |
| | |
| | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
Classical Dwarf Small Solar System Body Satellite
Planet Planet (e.g. most Solar System (e.g. Moon,
(clears orbit) (doesn't asteroids, TNOs, comets) Titan)
clear orbit)



--------------------------------
Possible compromise proposal
for future consideration
--------------------------------

------------------- Solar system bodies ----------------
| | |
Hydrostatic equilibrium, Not enough mass for Satellite
self-gravity produces hydrostatic equilibrium; of another
"nearly round" shape; and not a satellite of another body [other
not a satellite of another body [other than Sun] than Sun]
body [other than Sun] | |
| | |
Planet in broad sense | |
| | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
Major Dwarf Small Solar System Body Satellite
Planet Planet (e.g. most Solar System (e.g. Moon,
or (doesn't asteroids, TNOs, comets) Titan)
Planet clear
in strict orbit)
sense
(clears orbit)

Again, I'm not sure how clear these diagrams are, or how they might be
improved -- but your page is a very handy explanation of the vote.

That was all that was intended. I guess some kind of sci.astro
FAQ entry for "Is Pluto a planet?" is going to be required and
perhaps the page could help. Your diagrams go farther and cover
the whole classification scheme.

best regards
George

In sci.astro George Dishman wrote:

"Margo Schulter" wrote in message
...
In sci.astro George Dishman wrote:

much trimmed as we seem to be in agreement

Please let me say "indeed."

more trimming.

A curious question: Why did the supporters of 5B choose
"classical planet" rather than "major planet"? The latter
term seems to me much more familiar, comprehensible, and
pertinent to the issue of dynamical dominance.

Beats me. It made "classical" the antonym of "dwarf",
great for Trivial Pursuit but rather odd by any other
standard.

Yes.

If I were asked to define "classical planets," I might say
Mercury, Venus, Earth, Mars, Jupiter, and Saturn -- assuming
that we mean the ones known before the discovery of Uranus,
and still considered planets (since originally the Sun and
Moon were also "wandering stars," and therefore planets).
It might be interesting to ask at what point Earth was first
called a planet -- this could get into an interesting search
of people like Nicholas of Cusa in the mid-15th century. Maybe
a quest for another thread.

Anyway, getting back to the IAU. From a diplomatic viewpoint,
if I were trying to get supporters of 5A to consider a
not-too-unfriendly amendment, I'd definitely choose "_major_
planet" for something like 5B. Clearly one of their points,
maybe the main one, is that Pluto definitely belongs in a
category other than that of the eight major planets -- and
likewise with 2003 UB313, as well as Ceres.

Since I agree completely with the adopters of 5A that Pluto
isn't a major planet but a dwarf planet, with dynamical
dominance as the difference, I'd try to join with them in
crafting language that affirms this point. The "classical"
thing might obscure rather than clarify this dichotomy.

Another way of putting this is that in 5A, "planet" might
be said to have a specific meaning: a traditionnal "major
planet" that has cleared its orbit. In 5B or my variant,
"planet" has a generic meaning embracing two species,
"major planet" (orbit-clearing) and "dwarf planet" (not
orbit-clearing).

Indeed, though I think that opens up the original problem
of producing thousands of planets most of which are too
small to deserve that name given the traditional meaning
of the word.

Actually, at least in our Solar System, I'm not sure about
thousands if we mean "major planets plus dwarf planets,"
but some scores quite possibly at any rate. Curiously, I got
involved in a thread on this elsewhere where a planetary
astronomer pointed out that at the most generic level,
minor planets are planets, too -- which does get us into
the thousands, of course. I'd call a "minor planet" one
type of Small Solar System Body, to use the official term.

For me, there are various types or "quanta" of planethood; but
I agree that there are eight major planets in our Solar System,
and that in many contexts "planet" means "major planet." My
own approach would be to explain to people who ask "How many
planets are there?" that there are eight planets of the
familiar major type, likely a considerably higher number
of dwarf planets (e.g. Ceres and Pluto, each at one time
considered a major planet), and some ten thousand minor
planets catalogued so far, if I'm correct.

Incidentally this page gives an interesting history of
the use of "asteroid" versus "minor planet"

http://aa.usno.navy.mil/hilton/Aster...orplanets.html

Indeed a great page!


I think the public view might be that Ceres and the larger
bodies might be justifiably called "minor planets" while
the word "asteroid" is more apt for assorted small rubble.

Actually I like a minor-meso-major planet scheme like
Asimov's, but with "mesoplanet" having Ceres and Pluto (or
now 2003 UB313 or "Xena") as included rather than excluded
bounds -- very much like the "dwarf planet" category. I'd
say that the IAU criteria are good ones for the three
categories, whatever we want to call them.

[URL for your fine presentation repeated for convenience]

http://www.georgedishman.f2s.com/astronomy/planet.html

I am hoping to be more accurate in some of the grammatical
terms I am using but that's less important than getting the
understanding across.

Well, I guess we can each take another look and invite others
to join in, as you have done.

[On how people could see text of Resolution 5B and get
mistaken impression that it had passed.]

Actually I was one of those people until someone
mentioned the result. The IAU web site doesn't actually
highlight the vote results on their home page ... hold
the phone, yes it does now. There is now a link which
wasn't there when I went out a few hours ago. I haven't
had a chance to check in detail but the formal page
looks the same as 5A at first glance.

I'll have to have a look at this too.

[composed with monospaced font]

Excellent stuff Margo. I think this might best be laid out
as a flowchart. I had thought of producing a Venn diagram
but that approach isn't so effective. I had some trouble
with satellite as well because "is not a satellite" is not
a requirement for a planet. Perhaps that was left over from
when they were considering Pluto and Charon to be a double
system. Anyway it moves the test to another point in your
chart though I'm not sure where yet. Also the start point
should be "celestial body" rather than "Solar system bodies".
I'll have to look at this in more detail but if you don't
mind I'll add something like it to the web page.

Certainly, I'd be delighted to have it added to the page.

On the "is not a satellite," apart from the Pluto-Charon
question, one possible reason for not including it in
the definition of "planet" (i.e. my "major planet") is
that it might be redundant: a dynamically dominant body
which "has cleared the neighborhood around its orbit"
can hardly be a "satellite" of another body sharing that
neighborhood.

One point I confirmed by quickly checking Resolution 5A
as reproduced on your page: the exclusion of "satellites"
is actually mentioned before getting into the three
categories -- which might have influenced my diagrams:

"The IAU therefore resolves that planets and other
bodies in our Solar System, except satellites,
be defined into three distinct categories in the
following way:..."

Again, I'm not sure how clear these diagrams are, or how they might be
improved -- but your page is a very handy explanation of the vote.

That was all that was intended. I guess some kind of sci.astro
FAQ entry for "Is Pluto a planet?" is going to be required and
perhaps the page could help. Your diagrams go farther and cover
the whole classification scheme.

Please feel free to use my diagrams wherever they might be helpful.
By the way, I also considered a Venn diagram (maybe designed in
PostScript with regions in different shades of gray), but concluded
that it might be hard to pull off well in practice.


best regards
George



Best to you also,

Margo

On 05 Sep 2006 21:22:22 GMT, Margo Schulter
wrote:

In sci.astro George Dishman wrote:

--------------------------------
Possible compromise proposal
for future consideration
--------------------------------

------------------- Solar system bodies ----------------
| | |
Hydrostatic equilibrium, Not enough mass for Satellite
self-gravity produces hydrostatic equilibrium; of another
"nearly round" shape; and not a satellite of another body [other
not a satellite of another body [other than Sun] than Sun]
body [other than Sun] | |
| | |
Planet in broad sense | |
| | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
/ \ | |
Major Dwarf Small Solar System Body Satellite
Planet Planet (e.g. most Solar System (e.g. Moon,
or (doesn't asteroids, TNOs, comets) Titan)
Planet clear
in strict orbit)
sense
(clears orbit)

I agree that this looks better. Using Major Planet instead of
Classical Planet overcomes at least two known problems. One being that
these astronomers have forgot their astronomical history.

I should point out though that the IAU have already rejected Dwarf
Planets being classed within a collective planet group, which means
that this idea you will find the hardest to gain general support for.

Also while I am about it I consider all three diagrams flawed when
there is no size split in the satellites section, even though the
satellite grouping is fine. What I mean is that I always hate it when
some astronomer goes that they found another moon around a gas giant
and it turns out to be a oddly shaped pebble.

So I have always believed that there should be a split based on
hydrostatic equilibrium here as well. So that only your nearly round
objects are allowed to be called moons, where everything more minor
gets called as an orbiting asteroid instead.

So maybe that is just my personal gripe. Still, once you have finished
playing "What is a planet?" then you can start on "What is a moon?".
As if they don't stop their current method then soon enough your next
moon of Saturn will be the size of a football.

Cardman
http://www.cardman.org
http://www.cardman.com
http://www.cardman.co.uk

Margo Schulter wrote:

Margo, I'm going to trim severly and 'cherry pick'
your comments. Primarily this is because I have
given some thought to your alternative suggestions
and have gelled my own views a bit. The post was
getting rather long and I have no real disagreement
with the remainder of your comments.

In sci.astro George Dishman wrote:

"Margo Schulter" wrote in message
...
In sci.astro George Dishman wrote:

....

Anyway, getting back to the IAU. From a diplomatic viewpoint,
if I were trying to get supporters of 5A to consider a
not-too-unfriendly amendment, I'd definitely choose "_major_
planet" for something like 5B. Clearly one of their points,
maybe the main one, is that Pluto definitely belongs in a
category other than that of the eight major planets -- and
likewise with 2003 UB313, as well as Ceres.

Since I agree completely with the adopters of 5A that Pluto
isn't a major planet but a dwarf planet, with dynamical
dominance as the difference, I'd try to join with them in
crafting language that affirms this point. The "classical"
thing might obscure rather than clarify this dichotomy.

... My
own approach would be to explain to people who ask "How many
planets are there?" that there are eight planets of the
familiar major type, likely a considerably higher number
of dwarf planets (e.g. Ceres and Pluto, each at one time
considered a major planet), and some ten thousand minor
planets catalogued so far, if I'm correct.

....

I think the public view might be that Ceres and the larger
bodies might be justifiably called "minor planets" while
the word "asteroid" is more apt for assorted small rubble.

Actually I like a minor-meso-major planet scheme like
Asimov's, but with "mesoplanet" having Ceres and Pluto (or
now 2003 UB313 or "Xena") as included rather than excluded
bounds -- very much like the "dwarf planet" category. I'd
say that the IAU criteria are good ones for the three
categories, whatever we want to call them.

....

Well, I guess we can each take another look and invite others
to join in, as you have done.

....

On the "is not a satellite," apart from the Pluto-Charon
question, one possible reason for not including it in
the definition of "planet" (i.e. my "major planet") is
that it might be redundant: a dynamically dominant body
which "has cleared the neighborhood around its orbit"
can hardly be a "satellite" of another body sharing that
neighborhood.

My point on that is that (d) is redundant because an
object cannot be a satellite and also meet criterion
(a) that it be in orbit around the Sun.

OK, here's my alternative. Consider first Ceres, Pallas
and the other largest main belt obects. If say the top
tem had merged and were collecting the rubble then
they would approach being classed as a planet albeit
of very low mass. We already have a name for objects
which subsequently merge to form planets, that being
"planetesimal". As a result of our discussion, I would
suggest that Ceres etc. should be classed as remnant
planetesimals.

If Ceres and Pallas at some time came close and
became a binary, that doesn't change their individual
nature so I would further suggest they should then be
classed as a binary planetesimal system.

Looking then at Charon, it appears that if it were not
associated with Pluto, it would also warrant being
classed as a planetesimal hence the Pluto/Charon
system should be considered a binary planetesimal
(with two moons).

The boundary between binary and object/satellite is
a bit more difficult but could perhaps be resolved by
the mass ratio or location of the barycentre.

Similarly the distinction between a satellite and a
moon is unclear but let me suggest as a minimum
that a planetesimal in orbit around a planet should be
called a moon. The terms satellite and moon relate
to orbital configuration rather than mass and shape
so it would be both a moon and a planetesimal.

Objects not meeting the 'nearly round' criterion would
still be "Small Bodies" and further sub-divided into
the usual myriad classes (TNO, KBO etc.).

The criteria used by the IAU would still be applicable,
hence there would be eight planets in the solar system.
The definition could be easily rationalised to allow for
extra-solar planets by replacing "the Sun" by "a star",
even with the proviso that the current definition is
limited to the solar system since AFAIK there is only
one star in it ;-)

I will try to find time to draw this up as a flowchart, but
I have very limited opportunity over the next week, and
perhaps also add a test for fusion to identify stars
(including brown dwarf stars), free-floating 'planemos'
and binary planemo systems.

I would appreciate your views on the this proposal, in
particular the criteria for distinguishing binary from
object/satellite and what should qualify a satellite to
be raised to the status of a moon.

Note that this would mean that many of the moons of
the planets would also be classified as planetesimals
so the precedence of being a satellite and other
definitions might be contentious.

George

Margo Schulter wrote:
In sci.astro George Dishman wrote:

... The IAU web site doesn't actually
highlight the vote results on their home page ... hold
the phone, yes it does now. There is now a link which
wasn't there when I went out a few hours ago. I haven't
had a chance to check in detail but the formal page
looks the same as 5A at first glance.

I'll have to have a look at this too.

http://www.iau.org/fileadmin/content...n_GA26-5-6.pdf

There are two changes I have noticed. In the introduction
the wording ".. other bodies in our Solar System, except
satellites, be defined .." has been reordered as ".. other
bodies, except satellites, in our Solar System be defined
..." which is better grammatically but makes no difference.

Commas have been added in definition (3) changing
".. objects[3] except satellites orbiting the Sun shall .."
into "objects[3], except satellites, orbiting the Sun shall .."
which now means all satelites are excluded rather than
just those orbiting the Sun which makes a lot more sense.

Other minor points:

The quotes have been removed from "planets" in footnote 1.

Footnote 2 is still wrong, "either .. and" should of course be
"either .. or".

"Trans-Neptunian" has been capitalised in Resolution 6A.

George

Margo Schulter wrote:

If I were asked to define "classical planets," I might say
Mercury, Venus, Earth, Mars, Jupiter, and Saturn -- assuming
that we mean the ones known before the discovery of Uranus,
and still considered planets (since originally the Sun and
Moon were also "wandering stars," and therefore planets).
It might be interesting to ask at what point Earth was first
called a planet -- this could get into an interesting search
of people like Nicholas of Cusa in the mid-15th century. Maybe
a quest for another thread.

I asked that question and two closely-related questions
last November in the Bad Astronomy / Universe Today forum,
but didn't get definitive or authoritative answers.

http://www.bautforum.com/showthread.php?t=34542

The questions I asked:

Were the Sun and Moon commonly referred to as "planets" in
ancient times?

When was Earth first called a "planet", or described as a body
comparable to a planet, even if it wasn't thought to wander?

When were the stars first recognized as being like the Sun?

The answers I got were basically just:

The Sun and Moon were considered planets by early Greek
astronomers and are still considered planets in astrology.

Giordano Bruno suggested or asserted that that other stars
were suns with planets, like our own Sun.

I pointed out:

Lucian, a Syrian writing in Greek, in Athens, in the
second century AD, wrote a satire titled 'True History'
which described inhabitants of the Moon and the Sun.
That would seem to imply that he thought of them as
places something like the Earth.

And of course, the fact that the ancients knew that Earth
must be a sphere because of the shape of its shadow on the
Moon in lunar eclipses. But no answer to the question.

Margo Schulter wrote:

On the "is not a satellite," apart from the Pluto-Charon
question, one possible reason for not including it in
the definition of "planet" (i.e. my "major planet") is
that it might be redundant: a dynamically dominant body
which "has cleared the neighborhood around its orbit"
can hardly be a "satellite" of another body sharing that
neighborhood.

Obviously. No reason to mention an impossibility.

George Dishman replied to Margo Schulter:

My point on that is that (d) is redundant because an
object cannot be a satellite and also meet criterion
(a) that it be in orbit around the Sun.

All known satellites are in orbit around the Sun. There
is nothing redundant about (d).

-- Jeff, in Minneapolis

In article . com,
Jeff Root wrote:

http://www.bautforum.com/showthread.php?t=34542

The questions I asked:

Were the Sun and Moon commonly referred to as "planets" in
ancient times?

When was Earth first called a "planet", or described as a body
comparable to a planet, even if it wasn't thought to wander?

When were the stars first recognized as being like the Sun?

Probably around Copernicus' time. One prevailing argument against
a heliocentric solar system was that the Earth's orbital motion
around the Sun ought to cause a quite visible yearly parallax
among the stars --- unless of course the stars were extremely
distant and not just a little farther away than Saturn, as was
commonly believed in that time.

When the stars did turn out to be that vastly distant, they
must also be very bright --- like the Sun.

Herschel was one of the first trying to find the actual distance
to some stars, and he thought Sirius was some 3 light years away.


The answers I got were basically just:

The Sun and Moon were considered planets by early Greek
astronomers and are still considered planets in astrology.

Giordano Bruno suggested or asserted that that other stars
were suns with planets, like our own Sun.

I pointed out:

Lucian, a Syrian writing in Greek, in Athens, in the
second century AD, wrote a satire titled 'True History'
which described inhabitants of the Moon and the Sun.
That would seem to imply that he thought of them as
places something like the Earth.

And of course, the fact that the ancients knew that Earth
must be a sphere because of the shape of its shadow on the
Moon in lunar eclipses. But no answer to the question.

Erathosthenes (from ancient Greece) was the first to try
to measure the circumference of the Earth. His walue was
correct to within one percent or so -- much due to luck,
since he used a (by today's standards) very crude method.

Margo Schulter wrote:

On the "is not a satellite," apart from the Pluto-Charon
question, one possible reason for not including it in
the definition of "planet" (i.e. my "major planet") is
that it might be redundant: a dynamically dominant body
which "has cleared the neighborhood around its orbit"
can hardly be a "satellite" of another body sharing that
neighborhood.

Obviously. No reason to mention an impossibility.

George Dishman replied to Margo Schulter:

My point on that is that (d) is redundant because an
object cannot be a satellite and also meet criterion
(a) that it be in orbit around the Sun.

All known satellites are in orbit around the Sun. There
is nothing redundant about (d).

-- Jeff, in Minneapolis



--
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Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

"Margo Schulter" wrote in message
...
... A curious question: Why did the supporters of 5B choose
"classical planet" rather than "major planet"? The latter
term seems to me much more familiar, comprehensible, and
pertinent to the issue of dynamical dominance.


Possibly because some would regard only Jupiter, Saturn, Uranus and Neptune
as
"major". The inner planets might as well be grouped with Ganymede and Titan
as "minor" bodies, along with Pluto, Xena, etc.

wrote:
Pluto is out from planet dictionary
The researchers said Pluto failed to dominate its orbit around the Sun
in the same way as the other planets

For detail
http://www.studyandjobs.com/Pluto.htm

I've got this lively Astronomy book from 1959. It lists the 8 planets.
With the way things are going, we'll be discussing the confirmation of
canals on Mars, next.