Celestia Forums

Can anybody tell me where the models for galaxies reside in Celestia?
Is it possible to add a new model for the Milky Way?
Is there any information about galaxies in the forums or elsewhere? (I've looked but haven't found much)

Adam

Celestia's Galaxies are very simplistic, but you can replace them by models if you want.

Celestia's default galaxies aren't actually drawn using 3D models. Instead they're drawn using a rather simple algorithm internal to Celestia. Parameters controlling how the algorithm draws them are in the file Celestia\data\deepsky.dsc

Unfortunately, Celestia does not (yet?) allow DSC object definitions to be overridden by definitions provided in other files by a user, although that capability exists in v1.3.2 for SSC object definitions and has been added in V1.4.0 for STC object definitions. As a result, you currently have to edit deepsky.dsc itself in order to change how the Milky Way is drawn.

Also, Celestia's algorithm for drawing spiral galaxies is even more simplistic than the DSC Galaxy definition provides for. It can only draw galaxies which have two spiral arms, for example.

I've written an overly brief summary of the parameters that you can use in one of Celestia's DSC Catalog files to define a Galaxy. It can be found at http://www.lepp.cornell.edu/~seb/celestia/celestia_notes.html#7.0.

Does this help?

Written slightly later:

I forgot to mention -- if you want to use a real 3D model as a basis for a Deep Sky object, like for a galaxy, you have to declare it as a Nebula rather than a Galaxy.

Thanks Selden, that all helps enormously.

It's a shame about spiral galaxies. The Milky Way, it seems has the structure of a logarithmic spiral with 4 arms (and a pitch angle of 12 degs).

I wonder how easy it would be to modify the algorithm used to accept parameters from the DSC file such as number of arms and pitch angle (it would be beyond my rudimentary programming skills unfortunately). I have no idea if any catalogues routinely record parameters such as these, or whether it is only the classification (S0, SBa, etc.) that is recorded - I'm a bit new to galaxy structure. I came across a model for spiral galaxies in general and the Milky Way in particular in a paper by JP Vallee here: http://simbad.u-strasbg.fr/cgi-bin/aasbib?1995ApJ...454..119V if anyone is interested.

I might try to make a mesh for the Milky Way, but I haven't quite decided how to go about it yet.

Adam