GoodSeeing
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What the GoodSeeing score actually measures

One number from 0 to 100 per hour, combining cloud, transparency, seeing, moonlight and darkness. Cloud gates everything else — no amount of steady, dark air rescues an overcast sky.

The score is multiplicative, not an average. That is a deliberate choice: averaging lets a good component hide a fatal one, and in observing the fatal component is usually decisive. A perfect sky under total cloud is not a middling night, it is no night.

Cloud cover sets the ceiling. Transparency and seeing then modulate how good that clear sky actually is, moonlight scales it down, and darkness scales it again. Because the factors multiply, a single bad term drags the result down hard, which is the honest behaviour.

You can see the arithmetic for any hour. The microscope on every forecast page shows the cascade: it starts at 100 and attributes the points lost at each step, in the same order the code applies them. Nothing is hidden behind a proprietary index.

The score answers one question — is this hour worth observing in — and it deliberately does not know about light pollution at your exact spot, local topography, or whether the road to the site is passable. Those are yours to judge.

75–100 Excellent
55–74 Good
35–54 Fair
15–34 Poor
0–14 Clouded out
Best window Longest unbroken run scoring 35+ inside astronomical darkness

REVIEWED 2026-08-12 · SOURCES: MET Norway, sun and moon positions computed on our own servers

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Transparency vs seeing Transparency is how much light gets through the atmosphere. Seeing is how steady it is. They are independent, they often move in opposite directions, and which one matters depends entirely on what you are pointing at. Civil, nautical and astronomical twilight Astronomical darkness begins when the sun is 18° below the horizon. Above that, there is still measurable skyglow, and faint deep-sky work is compromised even though the sky looks black. Why the forecast changed since you last checked Weather models rerun several times a day on new observations. A night three days out routinely moves by twenty points between runs. A night tonight rarely moves much at all.

Check tonight