Celestia Forums

Hello,

I want to be able to view (the orbits, specifically) of planets, asteroids, moons, comets, spacecraft and the new dwarf planets separately. In Celestia's preferences there are view and label options for all but dwarf planets. Is there any easy way to add a class? Or will I just have to wait for Celestia 1.4.2? I want to manually edit the SSC files containing the IAU's dwarf planets (http://en.wikipedia.org/wiki/Dwarf_planet) so that my solar system will match the new solar system model.

Thanks,
Juz10mac

Celestia does not currently have a
Class "dwarf planet"
or
Class "pluton"
or
Class "small Solar System body"

Any such change will have to wait for at least two things to happen:
1. until the IAU actually votes and formalizes the new terminology, and
2. until the next release of Celestia.

In the mean time,
Class "planet"
Class "moon"
Class "comet"
and
Class "asteroid"
are available to describe natural orbiting bodies in Celestia,
Class "spacecraft"
is available for artificial bodies, and
Class "invisible"
is available for barycenters.

Whatever the final solution is, you can bet that the term "pluton" will never be used. Its proposal has already caused the geological community to snicker, and I'm sure caused some astronomical embaressment....

...John...

"Pluton" is officially off the list (as is plutoid, plutonid, or plutonoid...)

I can't believe the people on the IAU committee didn't know that "pluton" was a commonly used geological term. The excuse that they thought it was OK to use it because it wasn't in the MS Word dictionary is just... mind-boggling. These are supposed to be professional scientists and yet they failed dismally at basic research?!

Anyway. Perhaps we could have a "superclass" called "Planet" consisting of the "Major Planet" and "Dwarf Planet" subclasses, and then another "superclass" called "Small Solar System Body" consisting of the subclasses "Asteroid" and "Comet"?

According to latest reports, only 5% of the Astronomical community voted at the convention on the new definitions, and the ones who did not are NOT happy. According to criteria 3, a planet has to clear a large path of other objects in its vicinity. Jupiter would fail that criteria, since it has at least 63 "moons" and a whole clump of trojian asteroids nearly. Jupiter seems to gather space objects around itself. Earth also has not cleared the moon from its vicinity.

We may have to wait and see. Reportedly, a petition is already being circulated to void the definition.

Frank

fsgregs wrote:According to latest reports, only 5% of the Astronomical community voted at the convention on the new definitions, and the ones who did not are NOT happy. According to criteria 3, a planet has to clear a large path of other objects in its vicinity. Jupiter would fail that criteria, since it has at least 63 "moons" and a whole clump of trojian asteroids nearly. Jupiter seems to gather space objects around itself. Earth also has not cleared the moon from its vicinity.

No, Jupiter and Earth wouldn't fail that criteria. maybe it's not well defined, but the intent is clearly that if the object is embedded in a belt or swarm of similarly sized objects, then it's not cleared a path through other objects in its vicinity.

Jupiter has done this, Earth has done this, all the eight major planets have done this. Moons do not count as "other objects in its vicinity" here, they're referring to material that is in nearby circumstellar orbits, not circumplanetary ones. And the trojans don't count either since they're at the L4 and L5 points. Pluto, Ceres, UB313 and other bodies in the asteroid belt or the Kuiper belt haven't.

We may have to wait and see. Reportedly, a petition is already being circulated to void the definition.

I don't think that would get far. This whole thing has gone on long enough, nobody is going to want to reopen the debate unless someone spots a very serious and obvious flaw in the definitions, which isn't there as yet.

This was never going to satisfy everyone, but I think this definition is going to piss off the least number of people...

Not only that, but I find it hard to sympathize with people who are unhappy about the results of a vote, yet who did not vote themselves.

I agree, let the matter rest. No definition will ever please everybody, as Selden once mentioned. But really, enough is enough. Let's move from semantics and back to astronomical science.

(although I predict that this whole rotten can of worms will reopen as soon as New Horizons reaches Pluto)

...John...

the intent is clearly that if the object is embedded in a belt or swarm of similarly sized objects, then it's not cleared a path through other objects in its vicinit

Thanks for the clarification. However, I'm confused why Pluto would not meet the definition of a planet. Although it is technically in the Kuiper Belt, the nearest object to it anywhere near its size (excluding its three moons) is probably millions of km away. It's not like its embedded in a swarm of anything.

Here is a quote from the Associated Press on Pluto's status:

Pluto, a planet since 1930, got the boot because it didn't meet the new rules, which say a planet not only must orbit the sun and be large enough to assume a nearly round shape, but must "clear the neighborhood around its orbit." That disqualifies Pluto, whose oblong orbit overlaps Neptune's, downsizing the solar system to eight planets from the traditional nine

If this is one of the reasons, then the logic seems flawed. If Pluto is not a planet because it did not clear "Neptune" from its path, then Neptune is not a planet because it did not clear Pluto from its path! Nes Pa??????

Frank

Before adding a new "dwarf planet" category to Celestia, I'll wait to make sure that the IAU resolution regarding the definition of planets doesn't get overturned. If it doesn't, I'll change the object class in Celestia to match the new conventions more closely. I anticipate having the following:

- planet
- dwarf planet
- small body (short for 'small solar system body', subsumes asteroids and comets)
- moon
- spacecraft
- invisible

The only thing that Celestia uses the categories for is grouping objects for labeling and orbit drawing, so this isn't a major restructuring. The one exception is that Celestia only renders a tail for objects of class comet. This is inconsistent with how the object class is used elsewhere; I'd rather have some other means of specifying in an .ssc file that an object should have a cometary tail. A parameter for cometery tail brightness (with 0 indicating no tail) would do the trick and would also let you approximate the relative activity of a comet.

I also like the idea of getting rid of asteroid . . . 'small body' covers a wide range of objects that it feels slightly uncomfortable to label asteroids, such as KBOs and objects like Chiron that display cometary characterstics.

--Chris

Chris:

Using an ssc file for a comet tail could be workable, provided a user did not have to edit the ssc file every time the comet moved further along in its orbit so as to change tail length and brightness. That would be a bummer.

Rather, the tail should be drawn by Celestia automatically, with length and brightness changing as the comet gets closer or further from the Sun. I don't know if an ssc file would be the correct vehicle for that

Frank

fsgregs wrote:Chris:

Using an ssc file for a comet tail could be workable, provided a user did not have to edit the ssc file every time the comet moved further along in its orbit so as to change tail length and brightness. That would be a bummer.

Rather, the tail should be drawn by Celestia automatically, with length and brightness changing as the comet gets closer or further from the Sun. I don't know if an ssc file would be the correct vehicle for that

The parameter would just set a baseline brightness; the comet would still automatically vary in intensity based on insolation. Think of it sort of as the 'freshness' of a comet; comets on their first visit to the inner solar system tend to have a larger store of volatiles and produce brighter tails than comets that have spent more time near the sun.

--Chris

chris wrote:Before adding a new "dwarf planet" category to Celestia, I'll wait to make sure that the IAU resolution regarding the definition of planets doesn't get overturned. If it doesn't, I'll change the object class in Celestia to match the new conventions more closely. I anticipate having the following:

Judging by the behaviour of the IAU, it might be prudent to make Celestia's classes not hardcoded in the future. Perhaps a "declareclass" statement is needed in celestia.cfg?

(Then we'll be safeguarded against any IAU flip-flops)

I have a feeling that this decision won't hold... there's a growing revolt over it already.

Malenfant wrote:I have a feeling that this decision won't hold... there's a growing revolt over it already.

I've already sworn off the word "planet" anyway. From now on, I'm calling everything up there "worlds", I don't care how small they are...

...John...

And just because I am a repetative kind of guy, I will post this once more...

I think Rodenberry had it right...
http://en.wikipedia.org/wiki/Star_Trek_ ... ifications

I like this one better.

http://arcbuilder.home.bresnan.net/PCL01.html

and it has pictures :lol:

It's also the out of date page... and based on a whole set of fictional assumptions.

But it is fun to make!

...John...

Chuft-Captain wrote:

chris wrote:Before adding a new "dwarf planet" category to Celestia, I'll wait to make sure that the IAU resolution regarding the definition of planets doesn't get overturned. If it doesn't, I'll change the object class in Celestia to match the new conventions more closely. I anticipate having the following:

Judging by the behaviour of the IAU, it might be prudent to make Celestia's classes not hardcoded in the future. Perhaps a "declareclass" statement is needed in celestia.cfg?

(Then we'll be safeguarded against any IAU flip-flops)

Save for one base hardcoded classification (invisible), this makes perfect sense to me... very dynamic.

MKruer wrote:I like this one better.

http://arcbuilder.home.bresnan.net/PCL01.html

and it has pictures

Rendered in Celestia I might add.

Actually I rather like it that he used mass cutoffs for classificative purposes and the terms "planetesimal" and "planetoid". Rather more succint than "small solar system body" and "dwarf planet", now these are just clunky.

However this classificative scheme is based in current research and educated guesswork so I wouldn't throw it out so quickly. Actually I'm even using this classification system for my custom stellar system as it seems somewhat more straightforward while remaining descriptive.

Edit: Just now I realized the one of the above posters (Dollan) is quite probably one of the authors Excellent work you two have done though

After those last months, what about the IAU resolution; is this fully establised now?