What is the definition of a Moon?

[schlowi123]

I apologize beforehand for the probably rather "technical" text that follows.

Out of the discussion about ELW moons and shepard moons and nested moons I got curious.

That may seem as silly question, because I can just look at the system map. But what if I can NOT look at the system map?
If we formalize the first statement we probably would come up with sth. similar to the IAU definition of planet.

But how is that "formalized" in the name of a celestial body in ED?

I wonder, because several star/planet configurations exist.

Assuming that the system name is sth. like FOO BAR d123-321
i.: One star in the system
- If the system name is followed JUST by a number the body is a planet
- If the system name is followed by a number AND a (lower case) letter, the body is a moon.
- Example: Smojoo BC-B d1-0
- Planet: Smojoo BC-B d1-0 7
- Moon: Smojoo BC-B d1-0 7 a
- No problems with that.

ii.: Several stars in the system but NONE of them is in an orbit around another star … so NO "star at a planet position"
- The system name is followed by an upper case letter to indicate the star(s). So we get e.g. < FOO BAR d123-321 B 3 > if the body of interest is a planet.
- if it is a moon it is similar to the above case and we will get sth. like < FOO BAR d123-321 B 3 a >
- Example: Outorst TH-S c5-0 (one possible configuration of stars/planet) or Outotz VJ-P c6-0 (another configuration of stars/planet)
- Planet: Outorst TH-S c5-0 BC 1
- Moon: Outorst TH-S c5-0 BC 1 a (does not exist)
- No problems with that

iii. Several stars in the system and (at least) one of them takes the position of planet (and has "sub"-planets).
- This is were I have problems.
- I think Col 173 Sector EM-L d8-69 is such a system. If it is not, it illustrates my problems anyway.
- Planet: Col 173 Sector EM-L d8-69 AB 1 b
- Moon: Col 173 Sector EM-L d8-69 AB 1 b a
- And here is now the problem if one can NOT look at the system map but has just the name of the system. The body which I declare as a planet above has actually the name of a moon (as in case ii). And the moon has the name of a moon moon.

So my problem is now: how can I distinguish case ii moons from case iii planets if I just have the name of the celestial body?

One solution to the problem is, that the "planet" in case iii is the brown dwarf and that all bodies around it are moons … but this feels a bit unsatisfactory.

To make it (maybe) a bit easier: I work with the excellent EDSM database. They have many attributes for each celestial body and two of them can help with the problem: the first attribute is "parents", the second is "offset". The problem is though, that not all entries have the "parents"-attribute and offset = 3 does not necessarily mean that a planet is a moon. Hence I tried to work it out from the bodies-name.

I will be very thankful for all thoughts and ideas regarding my problem

With best regards from Norway … øhm I mean Explorers Anchorage

 

[iain666]

By your definition of moon excluding the bodies orbiting a stellar body that's in the horizontal line of the system map it is impossible to tell if body FOO BAR d123-321 A 7 b is moon or not without knowing whether FOO BAR d123-321 A 7 is a planetary body or a stellar one and that information is impossible to glean from just the name.

You're stuck, I'm afraid.

 

[Eahlstan]

You're stuck, I'm afraid.

He's stuck because 'Moon' is the name of the natural satellite of the planet named 'Earth'.
There is only one 'Moon' in the whole universe, all other bodies orbiting bodies other than Earth are natural satellites (which may have names like 'Ganymed' and 'Io').

This whole approach just doesn't make any sense.

 

[iain666]

The Moon is the only natural satellite of Earth. A moon is any planetary body orbiting another in a similar relationship. Mars has two moons, Jupiter has at least 79. There is no universally accepted definition of a moon.

As the OP is not a native English speaker you could take the meaning of 'a moon' that was implied by the body of the post and respond in kind, or you could be needlessly pedantic.

If you wish to be needlessly pedantic then I think it is only fair that you do so in Norwegian, and make sure that you make no mistake a Norwegian pedant could pick you up on.

 

[Eahlstan]

I know that some people say 'Moon' when they mean 'natural satellite', but that doesn't make it any better (in my opinion).
If I had been pedantic I would have mentioned, that there are no planets outside the solar system, because a planet's definition includes 'orbiting the sun'.
Additionally English is not my native language, therefore I'm already pedantic in more than one language

That said here's my actual response:

I didn't mean to sound pedantic or rude (and I'm sorry if I was, it's hard for me to foresee how my words affect others), I just wanted to express my opinion, that it's impossible to find something that isn't defined.
By schlowi's definition if 1I/ʻOumuamua some day is captured by a star without any orbiting object it would become a 'planet' (it would be named 'starname 1'), although no one would ever look at orbiting 1I/ʻOumuamua and say 'Oh that's a planet.'.

Another reason this whole thing is in vain is: There are no known limits to stars orbiting stars.
I.e. 'Dryoea Blue AA-A h32 B 2 a' is a star orbiting a star orbiting a star {[simplified as black holes are not stars (pedantry)] www.edsm.net/en/system/bodies/id/27328731/name/Dryoea+Blue+AA-A+h32 }.
No one could ever look at a body's name and say 'It's the nth orbiting object therefore it's not a star.'

 

[space voyager]

I know that some people say 'Moon' when they mean 'natural satellite', but that doesn't make it any better (in my opinion).
If I had been pedantic I would have mentioned, that there are no planets outside the solar system, because a planet's definition includes 'orbiting the sun'.
Additionally English is not my native language, therefore I'm already pedantic in more than one language

That said here's my actual response:

I didn't mean to sound pedantic or rude (and I'm sorry if I was, it's hard for me to foresee how my words affect others), I just wanted to express my opinion, that it's impossible to find something that isn't defined.
By schlowi's definition if 1I/ʻOumuamua some day is captured by a star without any orbiting object it would become a 'planet' (it would be named 'starname 1'), although no one would ever look at orbiting 1I/ʻOumuamua and say 'Oh that's a planet.'.

Another reason this whole thing is in vain is: There are no known limits to stars orbiting stars.
I.e. 'Dryoea Blue AA-A h32 B 2 a' is a star orbiting a star orbiting a star {[simplified as black holes are not stars (pedantry)] www.edsm.net/en/system/bodies/id/27328731/name/Dryoea+Blue+AA-A+h32 }.
No one could ever look at a body's name and say 'It's the nth orbiting object therefore it's not a star.'

There is only one Moon, but many moons. A word "moon" means a natural satellite.

 

[varonica]

The Moon is the only natural satellite of Earth. A moon is any planetary body orbiting another in a similar relationship. Mars has two moons, Jupiter has at least 79. There is no universally accepted definition of a moon.

As the OP is not a native English speaker you could take the meaning of 'a moon' that was implied by the body of the post and respond in kind, or you could be needlessly pedantic.

If you wish to be needlessly pedantic then I think it is only fair that you do so in Norwegian, and make sure that you make no mistake a Norwegian pedant could pick you up on.

Quite a few people over the years have found "extra" moons of the Earth, they have all alas turned out to be the result of an overactive imagination. The closest to a second moon we have is actually the Aten asteroid Cruethne which has a remarkable orbit that takes it around the Earth in a sort of horseshoe shaped pattern, so described as a co-orbital body to the earth since its orbital period is exactly the same as the Earths. Its orbit is described as "complex."

http://www.astro.uwo.ca/~wiegert/3753/3753.html

Having had a look through that I think when an astronomer describes an orbit as "complex" is about the same as a physicist describing particle physics as "difficult".

Anyway, point being, the Earth may not actually have a moon at all, the European Space Agency did refer to our system as being a double planet, although with the barycentre definately below the earth surface I think that's horsedung, it's a moon guys! However, in the year 3000? Still no, it will take a few hundred million years for the moon to get far enough away to move the barycentre above the earth surface.

https://en.wikipedia.org/wiki/Double_planet

As far as pedantry is concerned we are just beginners, scientists have us easily whipped.

We might look upon the Moon, then, as neither a true satellite of the Earth nor a captured one, but as a planet in its own right, moving about the Sun in careful step with the Earth. From within the Earth–Moon system, the simplest way of picturing the situation is to have the Moon revolve about the Earth; but if you were to draw a picture of the orbits of the Earth and Moon about the Sun exactly to scale, you would see that the Moon's orbit is everywhere concave toward the Sun. It is always "falling toward" the Sun. All the other satellites, without exception, "fall away" from the Sun through part of their orbits, caught as they are by the superior pull of their primary planets – but not the Moon.^{[URL="https://en.wikipedia.org/wiki/Double_planet#cite_note-Asimov-5"][SIZE=2][5][/SIZE][/URL][URL="https://en.wikipedia.org/wiki/Double_planet#cite_note-Aslaksen-6"][SIZE=2][6][/SIZE][/URL][URL="https://en.wikipedia.org/wiki/Double_planet#cite_note-PoV-7"][SIZE=2][Footnote 1][/SIZE][/URL]}
— Isaac Asimov

Fact is the nomenclature system used in ED is purely descriptive and not denominative, in other words the naming is not derived from the body it labels and so contains no reliable information about the body, in some cases you might guess from the name but that's just a guess. For instance binary bodies in primary orbit about a star are simply named consecutively, so 1 could be a single body, 2 and 3 a binary system and etc, no way to tell really.

I've never met a Norwegian pedant, are they really pedantic about pedantry?

 

[beneuto]

If I had been pedantic I would have mentioned, that there are no planets outside the solar system, because a planet's definition includes 'orbiting the sun'

Not quite correct as the definition of planet is for within the solar system only. That is to say, planets may be given a different definition in extrasolar systems and probably will due to the issues outlined by the OP. If and when that happens, they may then replace the current definition of planet with a single definition for all systems.

For my 2c, the naming is hierarchical based on what orbits what (as far as I am aware, ED doesn't make any actual named distinction between planets and moons). So this is a bit like parent and child. I am both a child of my parents and a parent of my children. Therefore perhaps the words planet and moon should be designations of the relationship between 2 bodies rather than the bodies themselves. Perhaps cutoff at a point similar to the solar planet definition because you have a draw a line somewhere for practical reasons.

BTW OP, shoutout to Norway from Australia. Have a Hansa beer and a packet of Smash for me!

 

[schlowi123]

I love you guys and gals!

First of all: thank you for the answer(s) … It is as I feared. In theory one can determine if a celestial body is a moon (with common understanding of moon) if ALL steps up to the body of interest are known. One does not need all celestial bodies up to the moon, just e.g. main star, second star, planet around second star, moon. But in practice the EDSM data does not contain this type of information for all bodies, thus I'm stuck ... Or well, I'm partially stuck, certain situations can still be identified.

Secondly: All of you are right … fortunately do I think that I am some kind of postmodernist, so this is no dilemma for me. And this is the reason why the ED community is so great … Some remark about nomenclature (no offense taken, I do this often enoug, too) lead to a serious discussion.

Third: My mother tongue is actually german, but I've been living in Norway since more then ten years and I'm pondering if I want to become a Norwegian. So

Fourth: As a physicist I would never claim that particle physics is "difficult" … because it is outright crazy … but these horseshoe orbits are really interesting and I recommend reading the short wikipedia description. It's probably a bit easier to understand since it has a nice diagramm that is very handy together with the explanation in the text

 

[Jackie Silver]

If you're working from bodies.json, I would suggest building a keyed dictionary of known stars with the star's body name as key, and then from your target name abstract the parent body name and search the dictionary, which should be very fast.

Not ideal but as has been noted there's no way to distinguish between "horizontal" star and planet.

W.r.t. "moon" - "moon" is absolutely commonly used in English to mean "satellite of a planet." One speaks of the moons of Mars, or the moons of any other planet. To say "the satellites of Mars" would be clumsy and non-intuitive and would potentially cause confusion as "satellite" carries the implication "artificial body", and to say "the natural satellites of Mars" instead of saying "the moons of Mars" would be very long-winded.