Dark Window

Go / no go for deep sky

Dark sky calendar

The next 30 nights for your location: how much of the dark is moon-free, the Moon’s phase, and the best windows to plan a deep-sky session around.

Nothing is sent anywhere: the math runs in your browser. Times use your device’s clock and time zone.

Questions

What is a dark night for astrophotography?
A night when the Sun is far enough below the horizon for full astronomical darkness and the Moon is below the horizon too, or only a thin crescent. Moonlight brightens the whole sky, washing out faint nebulae and galaxies, so the days around the new Moon are the prime time for deep-sky imaging.
What does moon-free mean here?
Moon-free hours are the hours of full astronomical darkness (Sun more than 18 degrees below the horizon) during which the Moon is below your horizon. A waxing Moon sets in the evening and a waning Moon rises after midnight, so even near the half Moon you may still get several moon-free hours at one end of the night.
Can I still image when the Moon is up?
Yes. Bright targets such as star clusters and the Moon itself do fine in moonlight, and narrowband filters (especially hydrogen-alpha) cut most of the glow for emission nebulae. Broadband galaxies and faint reflection nebulae suffer most. Keep the target far from the Moon in the sky.
How are the times worked out?
From the positions of the Sun and Moon at your latitude and longitude, calculated in your browser and shown in your device's time zone. Weather is not included: check tonight's cloud and seeing in the planner before you set up.

Open the Dark Window planner to check the weather and GO / NO-GO verdict for a night you pick.