Dark sky calendar
How many hours of real darkness each night has with the moon below the horizon. Plan your month around the nights that count.
Month
Night of
How to use the dark sky calendar
- Set your location with Use my location, or type latitude and longitude.
- Read the month at a glance: the number in each day is the hours of full darkness with the moon below the horizon. Highlighted days meet your good night threshold.
- Click a day to see its timeline from sunset to sunrise, with the moon-free stretches marked.
- Download the .ics file to put this month's good nights in your phone or computer calendar.
Questions
When is the next new moon?
The calendar marks every new moon, and the new moon calendar lists every one for this year and the next two, with the dark week around each.
What counts as a dark night?
Astronomical darkness, with the sun more than 18° below the horizon, and the moon below the horizon. You can choose to count a thin crescent under 10% or 25% lit as dark, since it does little harm.
Can I image when the moon is up?
Yes, with the right target and filter. Emission nebulae through narrowband or dual-band filters work well even near full moon. Galaxies and reflection nebulae need moon-free nights.
Why does it show zero hours in summer?
North of about 48.5° N, or south of 48.5° S, the sun never gets 18° below the horizon for weeks around midsummer. There is no true darkness on those nights, however clear.
How accurate are the moonrise and moonset times?
Checked against the US Naval Observatory, they agree to within a minute. Trees, hills and buildings on your horizon are not modeled.
Method
What counts as dark
Only astronomical darkness counts: the sun more than 18° below the horizon. Moon-free time is the part of that window when the moon is below the horizon. Rise and set use the almanac definition (upper limb on the horizon, with standard refraction), so the times match published tables.
A moon above the horizon but only a few percent lit does little harm to broadband imaging. If you choose a limit, nights with the moon at or below it count their whole dark window.
Accuracy
Ephemerides come from astronomy-engine. Against the US Naval Observatory for Amsterdam in October 2026, sunset, sunrise, moonrise and moonset agree to within a minute, and the four principal phases agree to within a minute. Local terrain, buildings and haze near the horizon are not modeled: a moon 2° up behind trees is still counted as up.
Nights at high latitude
In summer, north of about 48.5° N (or south of 48.5° S), the sun may never reach -18°. Those nights show zero dark hours. The imaging planner falls back to nautical twilight for such nights. This calendar does not, so a zero here means no true darkness.
Calendar export
The .ics file holds one event per good night, from the start to the end of its longest moon-free stretch, in UTC. Calendar apps convert it to your time zone.