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Celestia vs Universe Sandbox: catalog facts
Celestia	Universe Sandbox
Free Free and open source.	Paid One-time purchase from the website or Steam.
Windows, macOS, Linux	Windows, macOS, Linux
Free, real-time 3D exploration of space Move freely between planets, stars and galaxies	N-body gravity simulation using Newtonian mechanics Earth climate model you can alter
Project website blocks automated visitors with a proof-of-work check A simulator for exploration rather than a structured astronomy course	Paid only Needs a reasonably capable desktop computer
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.