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

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