Celestia Forums

Hi -- new forum member here, though I've been using Celestia for some time. I've been working on a novel set in the Main Asteroid Belt, and though Celestia has helped me with the orbits of the top few Main Belt asteroids, it only had a very few of them and wasn't helpful with the rest. So I went looking for add-ons and found only some very bad ones that were useless because they didn't list the asteroids by any names or numbers I could recognize.

Anyway, it then occurred to me to look for an update, and I found that there was now a Celestia 1.4.1 available to update my 1.3.1. Looking on the screenshots page, I found an image that showed the orbits of dozens, maybe over a hundred Main Belt asteroids:

http://www.celestiaproject.net/celestia/images ... oidorb.jpg

And naturally I assumed this was what I'd see if I installed the upgraded program. But even after completely deleting my old Celestia installation and starting anew with 1.4.1, I'm still only seeing the same half-dozen or so Main Belt asteroids that were there in 1.3.1. How do I get it to display all those others that are in the screencap? Or where do I find the add-on that contains them?

Thank you.

An addon with over 200,000 of the known asteroids is available on the MotherLode at
http://www.celestiamotherlode.net/catal ... don_id=785

A smaller one is there, too.

I think it would be useful to have an option in Celestia to just show the orbits and not the actual objects themselves. Could be useful for things like this, where you just want an idea of where the orbits are and how they're arranged. Plus it could save on computation time, so you might actually be able to see all 200,000 orbits at once if no bodies are rendered.

selden wrote:An addon with over 200,000 of the known asteroids is available on the MotherLode at
http://www.celestiamotherlode.net/catal ... don_id=785

A smaller one is there, too.

Those are the add-ons I mentioned above. They're useless to me because they don't catalog the asteroids by their actual names or normal catalog numbers, so I have no way of finding a specific asteroid by name. Also, for some bizarre reason they display the asteroids about a million times larger than their proper scale. Which I guess is fine if all you want is to generate a wide-angle screenshot showing the Main Belt in relation to the Solar System as a whole or something, but is no good at all if I want to get up close into the asteroid belt itself.

That's why I downloaded the 1.4.1 upgrade in the first place -- in the hopes that Celestia itself now had more asteroids included in its basic files. And if it doesn't, then what's the origin of that screenshot I linked to, the one with around a hundred Main-Belt asteroid orbits? It's clearly not from the add-ons at the Motherlode page, because it doesn't have the asteroids rendered larger than Jupiter. The data set used to generate that screenshot must exist somewhere, and that's what I'm hoping to find.

In principle I could use the program that I used to translate the MPC's smaller, specialized minor-planets files to translate their full database, which now lists 299,673 bodies. (Not right now: the program's at home and I'm not.)

If you have some not too complex selection criteria, I probably could accomodate that. I'm not sure if sufficiently reasonable radius values can be calculated from the H that is included in the database, though.

The SSC catalogs of the previous MPC files that I translated are available at http://www.lepp.cornell.edu/~seb/celest ... lanets.htm

P.S.
Another oops.

I just looked at the TNO file and discovered that the numbers in the names are truncated. *sigh*

I'll try to fix that this evening.

selden wrote:In principle I could use the program that I used to translate the MPC's smaller, specialized minor-planets files to translate their full database, which now lists 299,673 bodies. (Not right now: the program's at home and I'm not.)

Thanks, but I don't think I need that many. I know my desktop computer can't handle that many (too little memory). The abridged files from that Motherlode page ran for me, and they had about 3600 asteroids, which is no doubt plenty for my needs. So maybe the top few hundred or thousand Main-Belt bodies by size would be good. Also the most important thing is that they be listed by their names and/or catalog numbers (like 1 Ceres, 10 Hygiea, 704 Interamnia, etc.) so that I can track down specific ones by name. I couldn't figure out those catalog numbers that the Ducao add-on used.

The SSC catalogs of the previous MPC files that I translated are available at http://www.lepp.cornell.edu/~seb/celest ... lanets.htm

Yeah, I looked over those, but it's mostly NEOs, TNOs and Trojans, and I'm looking for Main Belt bodies.

Anyway, thanks for your answers. I'll be really grateful if you can help me out.

Check out this thread: http://www.celestiaproject.net/forum/viewtopic.php?t=9412

I created a tiny addon (5k) that adds the nine missing main-belt asteroids that are 250 km or larger in size.

This addon has the following asteroids:
10 Hygiea
15 Eunomia
16 Psyche
31 Euphrosyne
52 Europa
87 Sylvia
511 Davida
624 Hektor
704 Interamnia

It's not guarantted to be 100% accurate because I haven't verified all nine asteroids for correctness. However, other asteroids created with the same methods appear in the right places and two asteroids I checked against ephemerides were in the correct positions.

The addon includes CMS models for several of the asteroids. These are *very* rough models that only represent the overall dimensions of the asteroids.

It probably doesn't have the particular asteroids you are after but it's a start.

bdm wrote:Check out this thread: http://www.celestiaproject.net/forum/viewtopic.php?t=9412

I created a tiny addon (5k) that adds the nine missing main-belt asteroids that are 250 km or larger in size. ...

It probably doesn't have the particular asteroids you are after but it's a start.

It's a very good start! Thank you!! What I'm trying to do for starters is get a sense of where the major asteroids are and how they relate to each other orbitally, since I assume human settlers would congregate primarily around them. So this actually does have pretty much all the major ones I was looking for. It would also be good to be able to figure out which smaller ones are near those major "hub" asteroids at a given future date, but this is a good start.

Hmm.... come to think of it, having thousands of orbits displayed at once would be confusing. Is there a way to set it so that it only displays the specific orbits you select and not the rest? I mean, I know it highlights the orbit of whatever body you've selected even if you have the rest of the orbits turned off, but is there a way to have it keep that orbit highlighted while you highlight a second, a third, etc?

Also, is there a way to turn add-on files on and off, short of moving them in and out of the Extras subdirectory? Like, say, if I wanted to switch between showing just your biggest-asteroids add-on and another, more comprehensive one?

Unfortunately, enabling and disabling Addons and subsets of object types are functions that are not yet available in Celestia.

For now, you'll have to use some program external to Celestia to generate different catalogs that would be available when Celestia starts.

Class "asteroid" and Class "moon" really only change the colors of the orbits and labels of the bodies with those classes, so they could be used to indicate different categories of bodies.

A way to indicate the different types of asteroids at runtime would be to run a CEL or CELX script which contains Mark commands for a list of objects. That could be used to apply different Marks to the different categories. That'd just mark the bodies themselves differently, though. Their orbits wouldn't be shown differently.

I've created an Addon which displays 2140 of the more than 300,000 asteroids cataloged in "The Asteroid Orbital Elements Database" of Edward Bowell, which is described at ftp://ftp.lowell.edu/pub/elgb/astorb.html

The Addon is available at http://www.lepp.cornell.edu/~seb/celestia/astorb.zip
(290KB).

The selection criterion was that the body's diameter was included in the database. Apparently the IRAS satellite was used to study quite a few of them several years ago. As a side effect, all of them have catalog numbers, and almost all have formal names. There are a few that are still unnamed, though.

selden wrote:I've created an Addon which displays 2140 of the more than 300,000 asteroids cataloged in "The Asteroid Orbital Elements Database" of Edward Bowell, which is described at ftp://ftp.lowell.edu/pub/elgb/astorb.html

The Addon is available at http://www.lepp.cornell.edu/~seb/celestia/astorb.zip
(290KB).

The selection criterion was that the body's diameter was included in the database. Apparently the IRAS satellite was used to study quite a few of them several years ago. As a side effect, all of them have catalog numbers, and almost all have formal names. There are a few that are still unnamed, though.

That's pretty good, thanks. A bit of a glitch, though... your add-on duplicates some asteroids from the basic program and bdm's add-on, and they aren't in the same place. For instance, your (1) Ceres is about 1,335,700 km away from the basic program's Ceres, and your (10) Hygiea is nearly 20,000 km away from bdm's Hygiea. So you must be using slightly different parameters or something.

Still, on the scale of the Main Belt, that's still pretty close, and the errors don't seem to compound much as I go forward in time. So this should be of use to me. I'm very grateful.

Please feel free to edit the file to delete the asteroids you don't want to see, or to create a different file with just the ones you want. It's a plain text file, so your favorite editor should work fine. Hopefully it's obvious where the boundaries are for each entry: each one starts with a copy of the line that was read from the original astorb database.

I'd like to think that the orbital parameters are accurate in Lowell Observatory's astorb database. Supposedly they were generated just a few days ago using accurate ephemeides. (See the Web page mentioned above.) Celestia's parameters seem to have been obtained several years ago. On the other hand, the astorb values for radius probably have rather large errors, and it contains no rotational information whatsoever.

p.s. don't forget that these are simple Keplerian orbital parameters. They're only "correct" at the epoch (date) for which they're defined. That's why they're called "osculating parameters". The Keplerian ellipse "kisses" (is tangent to) the actual orbital path only at the one point at that specific time. Asteroids' orbits aren't perfect ellipses because of the gravitational influences of other bodies in the solar system. Celestia doesn't model gravitational effects at all.

selden wrote:Please feel free to edit the file to delete the asteroids you don't want to see, or to create a different file with just the ones you want. It's a plain text file, so your favorite editor should work fine. Hopefully it's obvious where the boundaries are for each entry: each one starts with a copy of the line that was read from the original astorb database.

I'm not much of a programmer, but I'll see if I can figure out how to do that. Or maybe I'll just live with the glitch. I'm using this more as a "geographic" reference than a realistic visual depiction, so having "twins" trailing the major asteroids is something I can live with.

I'd like to think that the orbital parameters are accurate in Lowell Observatory's astorb database. Supposedly they were generated just a few days ago using accurate ephemeides. (See the Web page mentioned above.) Celestia's parameters seem to have been obtained several years ago. On the other hand, the astorb values for radius probably have rather large errors, and it contains no rotational information whatsoever.

I guess as long as it's in the ballpark, it's okay for my needs.

p.s. don't forget that these are simple Keplerian orbital parameters. They're only "correct" at the epoch (date) for which they're defined. That's why they're called "osculating parameters". The Keplerian ellipse "kisses" (is tangent to) the actual orbital path only at the one point at that specific time. Asteroids' orbits aren't perfect ellipses because of the gravitational influences of other bodies in the solar system. Celestia doesn't model gravitational effects at all.

Is that why the bodies always seem to be a fair distance away from their orbital curves when you zoom in close? Or is it because the rendered orbits are made of line segments rather than being true curves?

Anyway, thanks a lot again. You've been very helpful.

The orbital paths drawn by Celestia are only rough approximations: straight lines between 100 samples along the "real" orbit. It's discussed in the "Preliminary Users FAQ" which is a sticky near the top of the Celestia Users Forum.