Sky Map Online

Real-time night sky chart for your current location. Shows stars, constellations, planets, Sun, and Moon. Point your device at the sky β€” the map rotates to match.

πŸ“ Location: β€” 🧭 Orientation: β€”
N S E W
βœ•
Magnitude: β€”
Altitude: β€”Β°
Azimuth: β€”Β°
Rise: β€”
Set: β€”
Stars
Sun
Moon
Planets
Constellation lines

How it works

This sky map performs all calculations in your browser β€” no data is sent to any server.

1. Your locationBrowser Geolocation API provides your latitude/longitude (or enter it manually). This determines which part of the sky is visible and the local horizon.
2. Sidereal timeLocal Sidereal Time (LST) is computed from UTC and longitude using the IAU 2006 formula, setting the celestial clock that maps RA coordinates to your sky.
3. Star positions~800 bright stars from the HYG catalog (magnitude < 5.5) are converted from equatorial (RA, Dec) to horizontal (altitude, azimuth) using the hour-angle transform: sin(alt) = sin(Ξ΄)sin(Ο†) + cos(Ξ΄)cos(Ο†)cos(H).
4. Planet positionsSun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn positions are computed via the astronomy-engine library (Jean Meeus algorithms) accurate to arcsecond precision.
5. Device orientationDeviceOrientationEvent provides compass heading (Ξ±) and tilt (Ξ²/Ξ³). The canvas rotates so the direction you're pointing is centered in the chart.
6. ProjectionAn azimuthal equidistant projection maps the whole sky to a circle: center = zenith, edge = horizon. Tap any object for its name, magnitude, rise/set times tonight.

Frequently asked questions

Why do I need to tap "Enable Sky Tracking"?
iOS Safari (iPhone/iPad) requires an explicit user gesture before it will grant access to the device orientation sensor (DeviceOrientationEvent). Without that tap, the browser blocks the API. Once you tap the button and allow access, the sky map automatically rotates to match the direction your phone is pointing. On Android Chrome and desktop browsers the permission is usually automatic.
How accurate are the star positions?
The chart uses J2000.0 equatorial coordinates from the HYG stellar database and converts them to your local horizontal coordinates using the IAU GMST formula. The result is accurate to within about 0.1Β° for stars β€” more than sufficient to identify naked-eye objects. Planets are computed by the astronomy-engine library (Meeus algorithms) to arcsecond precision. Precession and refraction corrections are not applied, which may cause small offsets (<1Β°) near the horizon.
What do the rise and set times mean?
Rise and set times show when an object crosses the mathematical horizon (altitude = 0Β°) today at your location, computed for the Sun's standard refraction correction (βˆ’0.833Β°) and geometric horizon (0Β°) for stars and planets. These are local times in your browser's timezone. Objects that never set ("circumpolar") or never rise are noted accordingly.
Can I use this without GPS?
Yes β€” tap "Enter location manually" and type your latitude and longitude. You can look these up on Google Maps (right-click any location). The star positions will be accurate for wherever you enter, though the orientation tracking will still require a device with a compass sensor.
Why does the sky map show the Sun during the day?
The chart shows all objects above the horizon regardless of daylight β€” this is useful for planning observations and understanding which constellations will be visible tonight. Stars near the Sun won't be visible with the naked eye due to daytime sky brightness, but their positions are still shown so you can see what's coming up after sunset.