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Celestia vs SpaceEngine: catalog facts
Celestia	SpaceEngine
Free Free and open source.	Paid A paid purchase, sold through Steam.
Windows, macOS, Linux	Windows
Free, real-time 3D exploration of space Move freely between planets, stars and galaxies	Seamless travel from galactic scale to planetary surfaces Real catalogued objects mixed with scientifically based procedural systems
Project website blocks automated visitors with a proof-of-work check A simulator for exploration rather than a structured astronomy course	Paid software Procedurally generated regions are plausible models, not observed data
Downloadable app	Downloadable app
Open source	Closed source
License: GPL-2.0	License not stated
No account needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 24, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.