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The sky in Sky Conditions

Stars are catalog objects, not randomly placed dots. The panorama covers 360 degrees of azimuth and 0 to 90 degrees of altitude. The selected target's azimuth is always in the centre, marked by a dashed vertical line. Cardinal directions, stars, the Milky Way, Sun and Moon rotate together when the target changes.

Sources

What the picture does and does not predict

J2000 catalog coordinates are transformed using the selected time and observer location. This wide-angle planning view uses the same sidereal-coordinate convention as the target cards; it is not a precision pointing chart and does not model proper motion, precession, refraction or terrain. A panoramic projection stretches features close to the zenith.

Twilight and the Moon above the horizon reduce sky contrast. Cloud layers then obscure stars locally, rather than multiplying the brightness of the entire sky by total cloud coverage. These are illustrative adjustments, not a calibrated prediction of naked-eye limiting magnitude. The Milky Way may be much less visible under local light pollution, haze or bright urban skies.

The Moon symbol uses the selected time's illuminated fraction and bright-limb angle from SunCalc 1.9. Its tilt is corrected by the observer's parallactic angle: crescents, quarters and gibbous phases are oriented relative to the local vertical, rather than always lit on one fixed side. The circular symbol is enlarged for readability, not drawn to angular scale or stretched by the panorama. Its faint dark disk and outline are locators, not an earthshine or visibility prediction. The Moon is omitted below the horizon; enabled cloud layers can obscure it.

Clouds represent the forecast for the observer's area, not the measured cloud positions along individual sight lines. They must not be read as a guarantee of a clear view toward a target. Solar and lunar data use SunCalc; weather forecasts use Open-Meteo.

The Weather checkbox is on by default and remembers your choice. Turning it off hides clouds and removes their dimming effect on stars and the Milky Way, without changing the weather readings below the map. Twilight and moonlight still affect the sky.

Weather time and cloud appearance

In Now mode, the page requests Open-Meteo's current model data, normally provided at 15-minute intervals. The displayed timestamp is the valid time of that value, not the time the page was refreshed. Current model data are not local observations. If missing or older than 30 minutes, the page explicitly labels its fallback to the hourly forecast.

For a planned time between two hourly samples, cloud cover and visibility are linearly interpolated. The selected time and both source hours are shown. This avoids jumps at half past the hour but adds no new meteorological information. Missing values are labelled n/a, never assumed to mean clear sky. Rain probability retains its separate hourly interval; it is not interpolated.

Clouds are seamless procedural textures: thin, streaked high layers and denser, shaded middle and low layers. Their coverage responds to the model's separate cloud levels. Their shape, optical thickness and bearings are illustrative assumptions, not measured properties or a directional cloud forecast. High cloud is drawn more translucent as a visual convention; real high clouds can also obscure the stars. Total coverage is not a measure of opacity, and cloud percentages at different levels are not additive.

See the Open-Meteo API documentation for current conditions, hourly variables and their time definitions.

Sky datasets are served by this website and loaded only when Sky Conditions is opened. No observer coordinates are sent to a star-catalog provider.