I wrote about this program a year or more ago. It's a free, 3-d astonomy program. This site says that it's, "The Celestia Motherlode is a repository for various addons like textures, models or celestial objects for Celestia."
Haven't tried it yet? I encourage you to do so.
BTW - I discovered this site form one mf my classmates, Jared K.
Still learning after all these years. :-)
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