Space Time
A free Stellarium alternative in your browser
Space Time is a planetarium the way Stellarium is: real star positions, real planet positions, your location, your sky. The difference is that you don't have to stay on the ground. The same scene keeps going from the grass under your feet to the cosmic web, and you can fly all of it.
🚀 Try it now, nothing to install Free · No account · Runs in any modern browser
The honest comparison
Most people searching for a Stellarium alternative find Stellarium Web first, and it's a much smaller product than the desktop app. Here is how the three actually stack up. We win some rows and lose some.
| Capability | Space Time | Stellarium Web | Stellarium (desktop) |
|---|---|---|---|
| Runs in the browser, nothing to install | Yes | Yes | No, install |
| Planetarium sky for your location & time | Yes | Yes | Yes |
| Leave the ground: fly the solar system in 3D | Yes | No | No |
| Continuous zoom out to the Milky Way & cosmic web | Yes | No | No |
| Stand on the Moon or Mars and look up | Yes | No | Sky only, via location |
| Spacecraft on real JPL trajectories, Apollo replays | Yes | No | No |
| Watch a solar eclipse from space (umbra on Earth) | Yes | No | No |
| Observing planner ranked for your site & night | Yes | No | Limited |
| ISS & satellite pass predictions (TLE + SGP4) | Yes | No | Plugin |
| Telescope & eyepiece field-of-view simulator | Yes | No | Oculars plugin |
| Star catalog depth | 118,000 (HYG, with proper motion) | Online surveys | Up to hundreds of millions |
| Telescope / mount control | No | No | Yes |
| Works fully offline | No | No | Yes |
| Plugins & scripting | No | No | Yes |
| Price | Free | Free | Free, open source |
What you get that Stellarium doesn't have
Stellarium shows you the sky from where you stand. Space Time does that too, then lets you go to the things you're looking at. Double-click Jupiter and fly there. Watch Shoemaker-Levy 9 hit it on the real July 1994 timeline. Ride along with the Parker Solar Probe, replay Apollo 11 from launch to landing, or watch the August 2026 eclipse's shadow cross the Atlantic from orbit. The planetarium and the spaceship are the same app.
When Stellarium is the better choice
We'd rather tell you straight. If you control a mount from a field laptop, want catalogs that go hundreds of millions of stars deep, need full offline use, or rely on its plugin ecosystem, install desktop Stellarium. It's excellent, it's open source, and Space Time doesn't replace it for those jobs. Where Space Time competes is everywhere else: the browser, the phone, the classroom, and every "what does the sky look like tonight" question that doesn't deserve a software install.
FAQ
Is Space Time a good alternative to Stellarium?
For browser use, yes: a real planetarium with a 118,000-star catalog and accurate ephemerides, plus 3D flight Stellarium doesn't attempt.
What does desktop Stellarium still do better?
Telescope control, deeper catalogs, offline use, plugins. For mount control from a field laptop it remains the right tool.
Is it really free?
Yes. No account, no download, no paid tier.
Does it work offline?
Not yet. It needs a connection to load, then runs fully client-side.