How the astrophotography forecast works
The Quiet Sky is an astrophotography weather app that runs in your browser, anywhere in the world. Compare the next seven nights, hour by hour, with cloud towards your target and usable imaging time for your rig.
Cloud along your line of sight
Pick a target and the forecast follows your telescope's line of sight through the low, middle and high cloud layers. We call this sightline cloud. The crossings marked on the map are the piercing points; a cloud deck is simply one of those layers.
Cloud well away from your site can block a low target even when the sky overhead is clear. If the target is too low for the sightline calculation, or its data is missing, you'll see overhead cloud, labelled as such.
The sky you can actually see
A clear spell is useful only while your target is in view. Save a site and record the trees, roofs or balcony that block your sky. The forecast then leaves hidden hours out of usable windows, and the planner uses the same skyline when choosing targets and times. The horizon tool traces it with your phone, no account needed, and gives you a horizon file for N.I.N.A. as well.
How the score works
Each dark hour gets a score out of 100. Cloud and twilight set the starting point, then moonlight, seeing, transparency, wind and dew take points off. Rain can cap the result.
Your rig makes a difference. For example, a narrowband filter reduces the Moon's effect on the score. The usable window is the longest unbroken stretch that meets your rig's threshold. The night labels run from Quiet, long clear stretches, to Closed in, overcast or otherwise not usable for imaging, and are based on the best stretch of the night. You can find the score thresholds in the FAQ.
Weather models selected for your region
Each night, we compare candidate cloud forecasts with weather-station observations in regions with saved sites. Those results help choose the model or blend used for each region, alongside checks on coverage, data freshness and update frequency. Where no regional choice is available, we use Open-Meteo's default forecast.
What the forecast shows
It reads like a clear sky chart: hour-by-hour rows for cloud, seeing, transparency and darkness, with cloud cover split by layer into low, middle and high cloud. Follow the cloud forecast map through the hours to look for clear skies around your observing site.
There's also seeing (how steady the air is), transparency (how clear it is), wind, dew risk and rain. Moonlight and darkness times sit alongside them, so you can see how much of the night is worth using.
The same weather data is useful for visual astronomy and stargazing. Check cloud, seeing and moonlight before taking out binoculars or a telescope. The night scores and usable windows are tailored to imaging.
Weather sources and updates
Open-Meteo supplies the hourly weather data, with models from services including the UK Met Office, ECMWF, DWD, NOAA, Météo-France and Environment Canada. Which models are available depends on your location and how far ahead you look. We also show Environment Canada's GEM cloud forecast as a second opinion.
Seeing and transparency come from 7Timer! where available, for roughly three days ahead. Outside that coverage, we estimate them from winds aloft, atmospheric instability and humidity. Copernicus Atmosphere Monitoring Service forecasts add information about smoke, dust and haze. Use seeing to compare nights at your site, rather than to predict star size.
Update times vary by source. The forecast has hourly steps, but a new model run may arrive less often. The Sources & licences page has the full credits.
Beyond the forecast
Once you have a night in mind, choose a target and work out the framing. Then plan the night from the time still needed through each filter, and track the project across nights as you collect it.
Read the astronomy weather guides for help interpreting cloud cover, seeing and transparency, and deciding what to check before setting up.
Anywhere you observe
Use a place name or coordinates to choose your site. Times are local to that site, and each night runs from sunset to sunrise. In places without full astronomical darkness in summer, the forecast uses nautical or civil darkness.
You don't need an account to check the seven-night forecast. It runs in your browser on a phone or computer, and you can add it to your Home Screen. You'll need an internet connection for forecasts.
Sightline cloud, saved sites and rigs, alerts, projects and the night planner require an account. The FAQ explains current access and pricing.