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The definition of a moon is a natural object (or satellite) that orbits a planet. To my understanding Saturn's rings are made up of space debris, and they must orbit around the planet. Does that mean that each individual piece of debris and dust in Saturn's rings, and other planet's rings, count as moons? 

Edited by Patrick2568422
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To my understanding there is no definitive answer for question "what is a moon?". Sure it must be natural object, but as far as I know there is no size definition....where would you draw the line?....

 

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Just now, Tuomo said:

To my understanding there is no definitive answer for question "what is a moon?". Sure it must be natural object, but as far as I know there is no size definition....where would you draw the line?....

 

I say it has to be big enough to be spherical. 

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from wiki

 

Definition of a moon

220px-Moon%2C_Earth_size_comparison.jpg
 
Size comparison of Earth and the Moon

There is no established lower limit on what is considered a "moon". Every natural celestial body with an identified orbit around a planet of the Solar System, some as small as a kilometer across, has been considered a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets. Small asteroid moons (natural satellites of asteroids), such as Dactyl, have also been called moonlets.[12]

The upper limit is also vague. Two orbiting bodies are sometimes described as a double body rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto–Charon system to be a double (dwarf) planet. The most common[citation needed] dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, because it depends on distance as well as relative mass.

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3 hours ago, Earl said:

from wiki

 

Definition of a moon

220px-Moon%2C_Earth_size_comparison.jpg
 
Size comparison of Earth and the Moon

There is no established lower limit on what is considered a "moon". Every natural celestial body with an identified orbit around a planet of the Solar System, some as small as a kilometer across, has been considered a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets. Small asteroid moons (natural satellites of asteroids), such as Dactyl, have also been called moonlets.[12]

The upper limit is also vague. Two orbiting bodies are sometimes described as a double body rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto–Charon system to be a double (dwarf) planet. The most common[citation needed] dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, because it depends on distance as well as relative mass.

so therefore. technically the little tiny bits of debris are moons.  

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On 15/08/2017 at 20:28, Patrick2568422 said:

so therefore. technically the little tiny bits of debris are moons.  

In practical terms though to refer to the ice particles forming the rings as "moons" would be pushing the point somewhat and generally misleading.  Similar argument for the definition of a planet that led to the excitement in certain media circles regarding Pluto etc.

 

Jim

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From the IAU site on naming astronomical bodies "Modern technology has made it possible to discover satellites down to 1 km in size or even smaller. " so it looks like it counts as a natural satellite as long as it has been possible to uniquely identify it so that it's discovery can be confirmed. 

Info from here https://www.iau.org/public/themes/naming/

Regards Andrew

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Angels, dancing on (heads of) pins ?

and this this business of the classification of Pluto (is it or is it not) was an exersize in agrandisment on the part of an ego & publicity,,, in my humble opinion,,,,   and demeans the dedication of ClydeT and his limited (state of the art?) equipment.

so there !

Edited by SilverAstro
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9 hours ago, SilverAstro said:

(state of the art?) equipment.

I feel the need for a google, when did silvered glass take over from speculum metal mirrors? I suppose (1930's) he was part of the Porter / Sprinfield / Stellafane group. One for the History section !

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12 hours ago, SilverAstro said:

Angels, dancing on (heads of) pins ?

and this this business of the classification of Pluto (is it or is it not) was an exersize in agrandisment on the part of an ego & publicity,,, in my humble opinion,,,,   and demeans the dedication of ClydeT and his limited (state of the art?) equipment.

so there !

Indeed, and all the while the universe cares not a jot what we call a planet nor a moon. Just human definitions with all the fragility that by default they must contain.:) 

Jim

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12 hours ago, SilverAstro said:

this business of the classification of Pluto (is it or is it not) was an exersize in agrandisment on the part of an ego & publicity,,, in my humble opinion,,,,   and demeans the dedication of ClydeT and his limited (state of the art?) equipment.

There's an interesting vid on utube (from 1980) where Clyde himself predicts that a lot more Pluto-like objetcs will be discovered and so the importance of his discovery will decline. So I think he would have been fairly stoical about the reclassification.

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39 minutes ago, saac said:

Indeed, and all the while the universe cares not a jot what we call a planet nor a moon.

Quite right but classification has been the basis for enabling us to study the natural world. It has allowed us to get to grips with the great kingdoms of life, understand carbon and inorganic chemistry and the stars above via their spectral types. While no such classifications are perfect they do enable science.

Clyde Tombaugh achievement is not diminished by the reclassification of Pluto but to my mind enhanced when you realise how long we had to wait and the degree of technological enhancement that was needed to discover more of the class of object he discovered.

Regards Andrew

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My point was that in all our qualitative taxonomies there are weaknesses when taken to the extreme or applied where they were never intended to be applied. A trivial example being "everything in the solar system (excluding the sun) is a planet as it orbits the sun.  That is clearly insufficient so we need to refine our definition to include clearing its own orbit and then having sufficient gravity to pull itself into roughly spherical shape. Further modifications evolve as each new challenge emerges. These definition suffer from such due to the looseness of their original conception and use. Referring to the debris  field forming the rings of Saturn as moons is a case in point.

Jim 

Edited by saac
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I wonder if in a way there is a parallel here with regards to the wonderful SI system. When defining base units we seek to root the definition of the unit to a truly fixed reference point using physical parameters. As an aside, I was reading somewhere recently that moves are afoot to remove the standard kg as the last physical standard. It's a shame in a way, I like the idea of a physical standard guarded as though it were treasure, which I guess it is really. :) 

 

Jim 

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Etymologically the word Moon has common origins with words for Month.  ;)
Though that clearly doesn't limit some modern usage. The question arose
elsewhere as to whether an Astronaut could have a satellite! Sadly it would
have to orbit within the body of the person... An "exercise for the reader"? :p  

Edited by Macavity
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4 hours ago, Macavity said:

 Sadly it would have to orbit within the body of the person... An "exercise for the reader"?

Errr ? I'm missing something (probably!) but barycenter has already been mentioned ?

If you and your missus were to go 'out there' beyond other influences you could each be the other's moon with a bary about half way betwixt  ( a few assumptions are always necessary :) )

Having been confounded by things like foot-poundals and slugs, progressed thro' cgs and MKS, I am all in favour of SI ( even tho' as an English I'd av preferred IS )  but dislike it's propensity for naming its units after personages of ever diminishing notoriety as they cast the net wider ( cycles per sec is expressive, Hertz is intellectual superiority/ snobbery  :( )

Edited by SilverAstro
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Quote

Exercise for the reader:

A subject, debate, or other matter that is not decided or dealt with directly by the author or presenter, but rather is left up to the judgment or interpretation of the observer, reader, or addressee.

Or as I would have once interpreted it: "Something I don't have to bother with..."! :p

Edited by Macavity
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As a postscript: Certainly not my wish to cause any chagrins... Due to repetition,
(I'd forgotten about barycentres!) OR via any subsequent choice of words. A wry
reference to a frequent text book author  phrase? And certainly no one here... :) 

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