About
AstroTools is an app and a website for planning astronomical observations. This page is a straight answer to where every number you see actually comes from.
Where the data comes from
Nothing on this site is invented — here is the full list of sources everything is built on.
All calculations run on the fly against this data, for the coordinates you picked. Nothing is cached for long: the forecast updates as its source does.
How the night score works
Cloud cover by layer, humidity, dew point, visibility and the wind shear between ground level and 120 m are folded into a single number from 0 to 100. The score is then penalised for a bright Moon — weighted by how many hours it is above the horizon — and for a lack of darkness: deep twilight and white nights cut it further the higher the Sun sits below the horizon.
80 and above is an excellent night for deep sky. 40–60 still works for the Moon and planets. Below 20 there is no point driving out. The app runs the very same algorithm, so the figures here and on your phone agree.
The app
The app keeps the same tools in your pocket: the forecast with clear-night notifications, an interactive cloud map, the light pollution map offline, ISS passes and a meteor shower calendar.
The author
I build AstroTools — the app and this site. Amateur astronomy, observing and code.
Get in touch
Found an error in the calculations, spotted data that does not add up, or have a suggestion? Write to me. I answer every message.