What this page shows: Clear Skies estimates how usable each observing night is for astronomy and astrophotography. It combines cloud cover, low/mid/high cloud layers, visibility, precipitation risk, precipitation amount, wind, and moonlight into a simple night score.
Location entry: You can use the location search box, enter a UK postcode, enter Lat / Lon manually, or tap Use GPS. UK postcode search uses postcode geocoding, while towns and cities still use normal place-name geocoding. Coordinates are useful for remote observatories, dark sites, and exact field locations.
Forecast button: Use GPS starts the forecast automatically. The Forecast button is mainly for manual entry, either from the search suggestion list or direct coordinate entry.
Saved location: After a successful forecast, the last location is saved in your browser. When you open the page again, the saved location is restored automatically and the forecast starts by itself. You can still replace it with a new search, new coordinates, or GPS at any time.
Weekly overview: Each day card represents the observing night that starts on that calendar date. In other words, the score includes the evening hours after dusk and the after-midnight hours before the next dawn. This is why the night does not belong to only one same-day block.
Selected night: This panel shows the detailed times for the chosen night: sunset, next sunrise, astronomical dusk, astronomical dawn, moon phase, moon rise/set, number of scored hourly blocks, and the best continuous 3-hour window.
Hourly window: Each box is one forecast hour with its own score. The score is shown from 0 to 10, where higher is better. The best 3-hour window shown above the hourly cards is calculated from these hourly scores.
Astro Darkness toggle: This is enabled by default. When ON, the hourly section shows only the hours between astronomical dusk and the next astronomical dawn. When OFF, the hourly section shows the full selected day, which is useful for checking daytime weather, twilight transitions, or planning setup and teardown.
How the score works: Heavy cloud is the biggest penalty. Low cloud reduces the score more than high cloud. Rain risk, rain amount, poor visibility, and stronger wind also reduce the score. If the Moon is above the horizon, bright moonlight further reduces the score, especially when the sky is otherwise clear.
Colours: The score colours are intentionally simple: greener boxes indicate better conditions, while redder boxes indicate poorer conditions. This makes it easier to compare nights and hourly slots quickly on mobile.
Night Mode: The Night Mode button switches the page to the same red-style observing palette used on Sky Planner. Most page text, controls, and interface elements turn red-toned to preserve dark adaptation more comfortably.
Data notes: Forecast weather values come from Open-Meteo. Astronomical dusk/dawn, moon phase, and moon rise/set are calculated locally in the browser using embedded astronomy logic, so the page can combine the weather forecast with night-sky timing for your exact location.
