Dark-night stargazing planner
Find the nights when the Sun is far enough below the horizon for a truly dark sky and the Moon is out of the way, so faint stars and the Milky Way show up.
Best nights
London, United Kingdom · Europe/London
Each bar runs from noon to noon. Times are local.
How the planner works
For each night, from noon to the next noon, the planner works out when the Sun is far enough below the horizon and when the Moon is up, then subtracts one from the other. The US Naval Observatory defines astronomical twilight as ending when the Sun's centre is 18° below the horizon; after that, scattered sunlight is fainter than starlight. That is the default. Nautical (12°) is a looser setting for bright targets or for summers far from the equator. The best nights are the ones with the most moon-free darkness.
Reading a night
Each bar shows day, twilight and darkness in deepening blues, with a silver band while the Moon is above the horizon. The figures give the dark window, the moon-free hours inside it and how much of the Moon is lit. A thin crescent low in the west brightens the sky far less than a gibbous Moon, so a night marked partly moonlit can still be good for bright clusters and planets.
Summer at high latitudes
In London there is no astronomical darkness for several weeks around the June solstice: the Sun never gets 18° below the horizon. The planner says so instead of inventing a window. Try the nautical setting then.
Sources
- US Naval Observatory, Rise, Set, and Twilight Definitions (civil, nautical and astronomical twilight).
Questions
What about clouds and light pollution?
The planner only knows the Sun and Moon. Check the weather forecast, and get away from street lights if you can: even a perfect moonless night looks washed out from a city centre.
Why does a night show no full darkness?
Near midsummer, away from the tropics, the Sun stays less than 18° below the horizon all night, so astronomical darkness never begins.
Can I use this page outside at night?
Yes, it works offline once loaded. Switch to the dark theme and turn the screen brightness right down; bright screens undo your eyes' adjustment to the dark, and dim red light disturbs it less than white.