Planetarium Screensaver
The Planetarium screensaver is a live star map of the night sky above you right now, showing constellations, the brightest stars and the visible planets. It is computed on your device from the current date and time, needs no data feed, runs in your browser, and ESC exits.
How the Planetarium screensaver works
The saver reads your device clock and chosen location, then computes the local sidereal time — the celestial coordinate that tells it which way the sky is turned.
A built-in catalogue of the brightest stars is projected onto a circular sky dome; only stars currently above your horizon are drawn, sized by their magnitude.
The visible planets are placed using the same orbital math as the Orrery, reduced to where they sit in your sky tonight.
Constellation figures and the N/E/S/W horizon are drawn so you can orient yourself, and it all turns slowly as the real sky does.
A worked example
Pick a location and the dome fills with the stars actually overhead — Vega high up, Orion tracing its belt, a bright planet labelled near the horizon. By day it notes the sky is too bright to see them, but still shows where everything is.
Settings & tips
- Location sets the observer's latitude and longitude, which decides what's above the horizon.
- Star & planet labels toggles the names on and off.
- Constellation lines recolours the joined-up figures.
Frequently asked questions
- Is this the real sky right now?
- Yes. It's computed live from your clock and location, so the stars and planets are placed where they really are in your sky at this moment.
- Does it need an internet connection?
- No. All the astronomy is calculated on your device from a built-in star catalogue, so it runs fully offline.
- Why can't I see many stars?
- If your location is in daylight the saver notes the sky is too bright. It also shows only the brightest stars, the ones you'd actually pick out by eye.
- How accurate is it?
- Star and planet positions are accurate to within a fraction of a degree — perfect for finding constellations, though not an observatory-grade ephemeris.
- Is it free?
- Yes — free, no download, no key, entirely in your browser.