The stargazing score combines cloud cover and moon illumination to estimate how good conditions are for observing the night sky. Cloud cover is the dominant factor — even the darkest location is useless under heavy cloud.
The Bortle scale measures light pollution from 1 (pristine dark sky) to 9 (inner-city sky). In the UK, the best accessible sites reach Bortle 2 to 3, found in areas like Northumberland International Dark Sky Park, parts of the Lake District, Snowdonia, the Brecon Beacons, and the Scottish Highlands. At Bortle 3, the Milky Way is clearly visible and dozens of deep-sky objects are observable with binoculars.
Moon phase matters: A new moon (0% illumination) provides the darkest sky. A full moon floods the sky with light, washing out everything except planets and the brightest stars. The best stargazing combines a new or thin crescent moon with clear skies.
Practical tips: Give your eyes 20 to 30 minutes to dark-adapt after arriving at your spot. Avoid looking at phone screens (use a red-light torch instead). The hours after midnight are often best, as the atmosphere settles and any remaining cloud may clear.