How to pick a clear night for observing
Sky transparency, cloud cover, humidity and the Moon — four factors that decide whether a session succeeds. Here's what to look at when planning.
An observer's most common enemy isn't the lack of a telescope — it's the weather. The good news: a clear night can be planned in advance if you know which numbers to watch.
1. Cloud cover by layer
An ordinary weather forecast shows total cloud cover, but for astronomy the cloud cover by altitude matters more. Thin cirrus high up barely affects a daytime walk, yet it quietly kills the view of faint objects.
In AstroTools cloud cover is split into low, mid and high layers, and the map shows how clouds move over the next few days.
2. Transparency and seeing
- Transparency — how clean the atmosphere is. It drives the visibility of faint nebulae and galaxies.
- Seeing — how steady the atmosphere is. It drives the sharpness of the Moon and planets at high magnification.
A clear but turbulent night is great for deep-sky objects, but planets will "boil".
3. The Moon
A full Moon washes out the sky more than any street lamp. For faint targets, choose nights near new Moon, or times when the Moon hasn't risen yet or has already set. AstroTools shows the phase, illumination and the Moon's rise/set times.
4. Light pollution
Even in perfect weather, city light pollution eats most objects. Sometimes driving 20–30 km out of town is enough. The light-pollution map in the app helps you find dark skies nearby.
In short
A perfect night means: few clouds in every layer, good transparency, a dark Moon phase and low light pollution. AstroTools scores such a night automatically and shows it as a single number — all that's left is to pack your gear.
Plan your observing with AstroTools
Weather, the Moon, light pollution and satellite passes — in one app.