More details are available at
http://www.lepp.cornell.edu/~seb/celestia/graticules.html#6
Here's an example of sky and planetary equatorial grids used with Mars:
It's available in
http://www.lepp.cornell.edu/~seb/celestia/cmod_grids.zip (52KB)
If you restore this Zip archive into your Addons (or extras) folder, it should create its files in all the necessary sub-directories.
10deg.cmod is a text file in the models folder. It draws yellowish grid lines in space. A red line is drawn at a longitude of 0 You can edit 10deg.cmod to change these colors as you wish.
The included example SSC catalog files mars-sky-grid.ssc and mars-surface-grid demonstrate the use of the model to draw grids around Mars.
The included example location SSC catalog files mars-sky-grid-locs.ssc and mars-surface-grid-locs.ssc demonstrate how to label the surface and sky grids around Mars.
Comments within the SSC files explain how to make versions for other bodies.
Grant Hutchison's AltSurface latitude and longitude surface texture Addon may be more appropriate in many circumstances. It's available at
http://www.lepp.cornell.edu/~seb/celestia/hutchison/grids.html
