A good night for stargazing needs four things at once: few clouds, little moonlight, a truly dark sky and low light pollution. The score combines all four for your spot and shows how they change hour by hour, so you can pick the best window rather than just the best night.
- Clouds
- the biggest factor. Even a thin layer can hide faint objects.
- Moonlight
- a bright Moon hides faint stars, galaxies and meteors; a thin crescent barely matters.
- Darkness
- the sky is only truly dark after astronomical twilight ends.
- Light pollution
- measured with the Bortle scale, from 1 (darkest) to 9 (inner city).