A sky you can understand and trust
Precision, with context.
A calculated position, a forecast and a recommendation answer different questions. SkyChrono labels them separately.
Calculated astronomy
Sun, Moon, planet positions, phase milestones, twilight and eclipse searches use Astronomy Engine. Civil times use the selected place’s IANA time zone and daylight-saving rules. Rise and set assume standard refraction and an unobstructed, sea-level horizon; the generic hills and trees are an illustration, not measured local terrain.
Star positions use the Yale Bright Star Catalogue, adjusted for precession and nutation. Proper motion is not included. Celestial markers are enlarged; their drawn sizes are not a physical scale.
Independent comparison checks
Our stored US Naval Observatory reference fixtures cover nine dates and locations: Oslo around both daylight-saving changes, the equator near equinox, Cape Town at both solstices, and Tromsø in polar day and night. The current test covers 117 Sun, Moon, twilight and illumination comparisons.
In those fixtures, the largest event-time difference is approximately 31 seconds and the largest Moon illumination difference is 0.29 percentage points. These results describe this sample. They are not a guarantee for every date, location, atmospheric condition or historical time zone, and are not a scientific certification.
Observing recommendations
Basic plans use object height, darkness and useful evening hours. Bright planets and the Moon must be at least 15° high after dusk. Constellation suggestions require the line stars above 10°, bright reference stars above 20° and the Sun below −12°. Suggested times are sampled estimates.
For nights within the forecast range, cloud cover and the chance of precipitation from MET Norway (CC BY 4.0) move suggested times toward the clearest hours; you can turn this off in the plan. Thin high cloud counts for less than low cloud, and fog counts in full. The forecast is hourly for about two days and every six hours after that, up to about ten days ahead. Moonlight and your selected surroundings affect faint-star recommendations. Forecasts older than three hours, missing values and times outside forecast coverage remain unknown. We do not measure local light pollution, atmospheric transparency or telescope seeing, and do not turn these estimates into a claimed probability of seeing an object.
Stories and constellation figures
The modern 88 constellations are named sky regions. The familiar line drawings and cultural figures are a different layer. Our researched stories name their tradition and link to institutional sources; they are not presented as a universal history of the sky. We do not invent myths for entries whose story has not yet been reviewed.
Recognition figures use d3-celestial under BSD-3-Clause. Interpretive illustrations do not move stars or determine astronomical visibility. Read the IAU explanation ↗
Your location and privacy
Recent places, last selected city, favourites and saved plans stay in your browser. A shared sky link contains its selected coordinates, time and view. We request location, sensor and camera permissions only when you choose the corresponding action.
For nights the forecast can reach, this site’s server asks MET Norway for the cloud forecast at the selected place, rounded to about 1 km; your address is not passed on. City search sends what you type to Open-Meteo through this site. Camera frames and orientation readings stay on your device; they are not uploaded or saved. Sensor placement is approximate unless a star match has been verified. Sensor and camera access stop when the view pauses, closes or the page is hidden.
The privacy policy has the full details, and the terms cover how the service may be used.
What is still being verified
Automated geometry, calculation, input and lifecycle checks complement testing on real devices. Physical iOS/Android, outdoor compass and camera validation, accessibility review, field performance and production load measurements are not claimed complete.