After nearly two years of development, Celestia 1.5.0 is now available. This is the biggest update of Celestia ever, with significant improvements in rendering quality, accuracy, and flexibility.
Celestia uses OpenGL 2.0 shaders to compute atmospheric scattering effects, giving a much more realistic appearance to planets with atmospheres. A Lunar-Lambert photometric model was introduced to more accurately model the reflectance characteristics of dust covered bodies such as the moon. Per-pixel lighting effects are used for better looking specular surfaces.
When accuracy is critical, Celestia can use JPL DE405 and DE406 ephemerides for planet positions and JPL's SPICE system for both spacecraft trajectories and planetary orbits. For space mission simulations, spacecraft attitudes can now be specified with time-tagged lists of quaternions. A new system for specifying reference frames means that attitudes and positions can be supplied in whatever frame is most convenient.
Celestia's data files have been kept up to date with the latest astronomical discoveries: newly found natural satellites and extrasolar planets are included in the solar system catalogs, binary
star orbits have been updated, and the near star catalog incorporates new data from RECONS. The galaxy catalog has been updated with new distance estimates and the complete local group of galaxies.
Scripting improvements in version 1.5.0 make Celestia more customizable than ever before. There are now hooks that allow scripts to control the position and orientation of objects. With event hooks, scripts can capture keyboard and mouse input. Finally, scripts can be written to draw custom graphics using a new set of GL drawing functions.
A much more thorough list of the new functionality in Celestia 1.5.0 can be found here: http://www.shatters.net/celestia/150-feature-summary.html