How to pick a good night for stargazing: clouds, Moon, darkness and dew
A clear forecast is only the start. The five things that decide whether a night is good for looking up, how to read them, and the small habits that turn an ordinary evening into a great one.
Five things decide a night
Stargazers check the same things before every night out: clouds, the Moon, how dark the sky is (time and place), how clear the air is, and how damp it will get. A night can be cloudless and still poor if a bright Moon is up, and a hazy suburban night can still be great for the planets.
Our stargazing score for each city rolls the first three into one number per hour, so you can see at a glance when tonight is best. The rest of this guide explains what sits behind it.
1. Clouds: read the layers, not just the icon
A weather app's sun-or-cloud icon hides a lot. Look at cloud cover by the hour and, if your forecast shows them, the layers: low cloud blocks everything, while thin high cloud (cirrus) lets bright stars and planets through but washes out the Milky Way and faint objects.
Clear spells often come right after a cold front passes: the air behind it is drier and more transparent. Satellite cloud images and hourly forecasts are more useful than a daily summary.
2. The Moon: the biggest light in the sky
A full Moon brightens the whole sky so much that only the brightest few hundred stars remain. For faint targets (the Milky Way, meteors, galaxies) the best nights are the week around new Moon, or any night after the Moon has set or before it rises.
The Moon rises about 50 minutes later each night. So a few days after full Moon you get dark early evenings, and a few days before new Moon you get dark skies all night. Check moonrise and moonset, not only the phase. The Moon itself is a wonderful target too, best around first quarter when shadows along the terminator show craters in relief.
3. Darkness: twilight and where you stand
After sunset the sky goes through three stages of twilight. It is only fully dark when the Sun is 18° below the horizon (the end of astronomical twilight), about 1.5 hours after sunset at mid latitudes and much later near midsummer in the north. In summer at high latitudes it never gets fully dark at all.
Place matters as much as time. Moving from a city centre to a dark rural site can take you from a few dozen visible stars to several thousand. Even within a city, a park away from streetlights, with your back to the brightest glow, helps.
4. Transparency and seeing: two kinds of clear
Transparency is how clear the air is: dust, haze, smoke and humidity dim faint stars. It is best after rain or a front, and at higher altitude. Seeing is how steady the air is: on poor-seeing nights stars twinkle hard and planets wobble in a telescope.
They don't always go together. A hazy, calm night can be poor for the Milky Way but excellent for the Moon and planets, while a crisp, windy night after a front is ideal for wide views but makes planets shimmer.
5. Dew and cold: the comfort factor
When the air cools to its dew point, moisture settles on everything: lenses, eyepieces, binoculars. If the forecast temperature and dew point are within a few degrees, expect dew. A lens hood, a dew heater strip, or simply keeping optics pointed down when you are not using them helps.
You will also be colder than you expect, because standing still at night chills fast. Dress one layer warmer than the forecast suggests, and bring a reclining chair: looking up for an hour is much easier lying back.
On the night: let your eyes adapt
- Give your eyes 20–30 minutes in the dark. One glance at a white phone screen resets much of it; use a red light and the dimmest screen setting.
- Look slightly to the side of a faint object (averted vision): the edge of your eye is more sensitive in the dark.
- Start with something easy (the Moon, a planet, a bright satellite pass) and work toward fainter things as your eyes adapt.