A few questions about units in Celestia

[Apollo7]

Well I have a few inqueries here. First when I set up my solar system I like to pass a "Mass" field to Celestia for each planet and Moon I create. This is as much for my own desires as the need for accuracy, however, does Celestia actually USE the Mass identifier? Also, I describe mass in terms of Earths, i.e. a gas giant having 100 times earth mass, and a small asteroid having just .000000002 Earth masses, am I doing this correctly or does the mass argument need to be in kilograms or even grams?

In the atmosphere section, what is the atmosphere height listed in terms of? I presume its kilometers, but I'm not at all sure, also how is such a field determined. I notice in Celestia that both Earth, Titan and Venus have an atmosphere height of 60, whereas Mars, with a pressure at the surface which is much less than either of the preceiding 3 has a height of 30, and Trition a height of 1. Any help here?

Cloud speed is also a mystery, is this in Km/s? m/s? or some other value, Cloud height? is this in kilometers? let me know. Thanks.

[selden]

Some of your questions are answered by Thomas Guilpain's SSC documentation at http://members.fortunecity.com/guilpain/Fichiers%20ssc_uk.htm

[Apollo7]

Interestingly enough I found out shortly after using the globular generator for the first time that you can not have the cool gas-giant atmosphere effect (and make it work that is) without the planet having 0 Oblateness. Anyone who has ever looked at a picture of Saturn can see that the planet is the most visibly oblate of any in the solar system. Unfortunately the atmosphere seems to "detach" from the surface when you change the oblateness. A pitty to be sure.

[selden]

Which version of Celestia are you running?

Chris spent a lot of time getting atmospheres to do the right thing around oblate objects in the current series of prereleases. I think that code was included starting with 1.3.1pre4 or thereabouts.

[Apollo7]

I don't get into the pre-releases so I'm still using 1.3.0 and I'm eagerly awaiting 1.3.1. Is there any reason why a planet that orbits beyond 30 AU should look darker than if its at 10 AU? for some reason I've got a planet/texture combo that simply looks very dark, and I can't seem to lighten it up. The texture is a white-snow surface so the fact that it appears dark and gray is weird enough. Cheers.

[selden]

Avoiding "pre-releases" is up to you, of course.
Personally, I have too much fun playing with the new features And bug fixes.

The darkness at large distances is a bug in v1.3.0. I just tested it with a copy of the Earth orbiting at 40AU. It's dark in v1.3.0, but v1.3.1pre3 and pre9 both draw it just as bright as at 1AU.

Unlike some commercial software, the only substantive difference between Celestia's prereleases and a final release is that the developers make the distribution kits of the final release available on SourceForge. My experience (which started with v1.2.5) has been that very seldom do the prereleases introduce major new bugs in old features. In fact, the worst bug of recent times was introduced when Chris tried to fix a normalmap bug in v1.3.0final and managed to break bumpmaps entirely That bug is fixed in the v1.3.1 prereleases.

[Apollo7]

Well a few cosmetic tweaks aside my system is pretty much finished, is there someplace where I could post it? I used various textures which are not included with Celestia so that may present a problem. I'm still trying to get some things to look right but after all this time its looking pretty good.

At least the darkness problem wasn't of my own dooing, I'm noticing it on two of my planets that orbit beyond 30 AU of their primary. Although it seems to effect the Gas Giant less for some reason. I haven't added asteroids or comets yet to my system, that may be more tedium than I wish to engage in, but only time will tell. The system includes 7 planets and 29 moons at present. There are 4 gas giants, and a total of 4 moons with substancial atmospheres (one of which is the "Terran" planet of this system).

I still need to fix the obliquity of some of my planets. One of the giants is tipped by 69 degrees and that requires some alignment of moon axises that I have not done yet. Anyway things are going pretty smoothly anyway. Cheers.

[Evil Dr Ganymede]

I dunno, if a planet is dark at 30 AU from the star, I'd say that's actually fairly realistic

[Apollo7]

I agree that a planet getting darker as it moves farther away from a star is realistic, but, I also know that whats the point of creating a super-bad-ass planet at 10,000AU and having it be nothing but a black spot against a background of stars. I'm not developing this program but in some ways I guess realism does have to give way to practicality. Of course, having moons with radii under 200Km visible as square dots at 1AU can be somewhat disconcerting. I don't know a light scaling routine would be cool, but would everyone really like it?

[chris]

Of course, having moons with radii under 200Km visible as square dots at 1AU can be somewhat disconcerting.

The problem with moons appearing as bright square dots should have been fixed in the 1.3.1 prereleases. I just verified that Phoebe is not visible from a distance anywhere close to 1AU. The moons may be slightly bright still, but not nearly like they used to be.

I'm not sure what's going on with this light reduction at large distances from a star. It's not something that I'm seeing in my version--at least, Quaoar looks to be every bit as bright as say Venus.

--Chris