Every city page answers one question: is tonight worth going outside? The score is a shortcut, but the details tell you what kind of night you are getting.
Start with the score
Scores run from 0 to 100. Anything at or above 70 is a night most people should consider; 50 to 69 means compromise on clouds, Moon, or duration; below 50 usually means the sky is working against you. A score of “no darkness” is not a failure. In far-northern summer weeks the Sun never drops far enough below the horizon for true astronomical night, so the site deliberately refuses to invent a number.
Find the dark window
The dark window is the stretch between the end of evening twilight and the start of morning twilight. We show astronomical darkness first because it is darkest. When the Sun never reaches that depth, the site falls back to nautical, then civil twilight, and labels the result. A shorter window can still be excellent if the sky is clear.
Read cloud cover as a range, not a promise
The cloud percentage is an average across the dark window, with a worst-case peak beside it. An average of 20% with a 70% peak means there may be a long clear stretch and a rough patch. Hourly strips show when that patch arrives. Percentages above 85% suppress the “best window” suggestion because no two-hour slot is reliably clear.
Check the Moon line
A bright Moon is not automatically bad. A low crescent in the west leaves most of the sky dark. The Moon panel reports illumination, altitude, and whether it is up during your dark window. Moonless minutes are counted separately, which matters for faint targets like the Milky Way.
Use the reasons, not just the number
Beneath the score, each adjustment is listed: clear sky, long darkness, Moon penalty, precipitation, gusts, humidity, or a twilight cap. If the number surprises you, the reason list explains it. That is the whole design goal: no black-box score.
Sources and review
Updated October 21, 2026. Date-sensitive details can change.