Enter a ZIP code or city for tonight’s true darkness — the stretch when the sun is more than 18° below the horizon and the moon is out of the sky.
True darkness is the stretch of night when nothing is lighting your sky. Two things have to be true at the same time. The sun has to be far enough below the horizon that its glow has drained out of the atmosphere. And the moon has to be below the horizon too.
Almost every source gives you only the first one. That is why a site can tell you it got dark at 9:14, and you can drive two hours out of town, set up, and still see almost nothing.
Until the sun is more than 18° below the horizon you are still in twilight, even when the sky overhead already looks black to you. The glow fades in three recognised stages:
Past −18° the sun is finished. Astronomers call that astronomical night, and it is where almost every other tool stops. It is half an answer.
A gibbous moon riding high at midnight washes out faint objects just as thoroughly as twilight does, and no amount of −18° fixes it. A full moon at altitude puts the sky somewhere around Bortle 5 no matter where you are standing — which is why the moon is not a caveat on the definition, it is half of it.
So the number at the top of this page is a moonless night figure, both conditions met at once. The timeline shows the difference directly — moonlit hours washed pale, true darkness black and full of stars, and a strip underneath marking exactly when the moon is up.
How much it costs you depends on the phase and on how high the moon is riding. A thin crescent low in the west takes very little and sets early. A half moon costs you the faintest objects. Past three-quarters you are looking at planets, double stars and the moon itself — a fine night, just not a Milky Way night. If you are working out the best time to stargaze — or the best time to see the Milky Way — the moon matters more than the month.
Observatories schedule their faint-object work on the same two conditions and call it dark time, as opposed to grey time and bright time. This page draws the line at the horizon. If the moon is up at all, the time is not counted as true darkness. That is stricter than an observatory would be — they would call anything under about a quarter lit dark time and schedule faint work in it — but it keeps the number honest, it never promises you a sky you are not going to get, and it is why the page always tells you what time the moon sets. Wait it out and the rest of the night is yours.
Between 70 and 110 minutes across the lower 48, and the number moves with where you are and what month it is. The further north you go the shallower the sun’s angle, so the longer it takes: about 75 minutes in Key West in March, closer to 105 in Seattle in June. Summer is slower than winter everywhere, and the fastest handoff on Earth is near the equator around the equinoxes, where the sun drops almost straight down and the whole thing is done in about 70.
That is the sun alone. Add a moon above the horizon and true darkness does not arrive until the moon sets, which is why the timeline above shows both.
The end of nautical twilight is the trap. The sky looks black, the bright stars are up, and it feels like the show has started — so people take their photo, decide the sky is nothing special, and drive home. They left about half an hour before true darkness arrived. It was dark when they packed up — it just was not that dark yet.
The other one is latitude. Above roughly 49°N — the northern edge of Washington, Montana, North Dakota, Minnesota, Maine — true darkness never arrives at all for several weeks around the June solstice. The sun stays inside that last 18 degrees all night. Search a Seattle ZIP against a Portland one in late June and you can watch the window shrink to almost nothing. If this page tells you there is no true darkness tonight, that is not a bug.
Clouds, humidity and haze do their own damage, and none of that is astronomy. And a dark hour is not the same as a dark sky — you can hit perfect moonless true darkness in a Bortle 8 city centre and still count about nine stars.
Getting all four right at once — the hour, the moon, the weather and the place — is what separates a memorable night from a cold drive. This page handles the first two.
Knowing when the sky goes dark is useless if the sky above you never does. Here is how to find dark skies within driving distance of wherever you are — free, and written for people who have never done this before.
Find dark skies near youTimes are calculated locally in your browser — the NOAA solar position algorithm for the sun, an abbreviated lunar theory for the moon — at the centroid of the ZIP code or city you enter. Checked against a full ephemeris, sunset and the twilight times land within a few seconds and moonrise and moonset within a minute. Elevation is not accounted for; a mountaintop sees the sun set slightly later than the valley below it. Coordinates and time zones come from public US postal data.