Nyx: Dark Sky Planner

Which park, and which night? Nyx compares the 63 US national parks night by night and gives each a Darkness Score from 0 to 100, from the Moon, the clouds, the sky glow and the hours of true darkness. It tells you what it doesn't know. Free. No account, no ads, no tracking.

ONE SCORE, WITH ITS REASONS Four parts add up, and the weakest can cap the total, so a cloudy night never looks good. The line under the score names the cap. Park closures from the National Park Service sit beside the number.

PLAN See tonight's darkest parks within a straight-line radius, or sort every park by darkness. Choose a park and see its month as a calendar, with the best stretch of nights marked. Scrub thirty nights on a timeline and watch the Moon change shape. Give Nyx your free nights and it suggests a park for each. Times are always park-local.

AN HONEST FORECAST For the next few days the cloud forecast counts in full. Further out it is eased toward each park's usual clouds for the month, and beyond the forecast the usual clouds count alone; those nights say so. Three weather models are compared, with the range drawn when they disagree. Cloud layers, dew, cold and wind are shown for the dark hours, and heavy smoke can cap the score.

WHAT'S UP TONIGHT Each park's night lists the Milky Way core with its rise, highest point and Moon-free hours; the planets; meteor showers with a rate range; and lunar eclipses the park can see. These are reasons to go. They never change the score.

FIELD MODE At the park, "I'm here tonight" opens a red, dimmed screen for night-adapted eyes: a countdown to true darkness, each milestone of the night, and a dark-adaptation clock. "Where to look" turns the real sky to wherever you point your iPhone, with no camera. A Live Activity keeps the countdown on the Lock Screen, and alarms can wake you for true darkness or the core's rise.

ON YOUR WRIST AND IN THE ROOM On Apple Watch: tonight's score, the Digital Crown to look ahead, a dark-adaptation clock that taps your wrist, and complications that turn red at dusk. On Apple Vision Pro: stand under a park's computed sky on a chosen night, with star names and constellation figures, and place the Moon on your table, lit at its true phase. On iPad: the calendar and a park side by side.

SKY GLOW AND ACCESS Each viewing spot shows how its sky glow compares with the other parks, from NASA's Black Marble night-lights data, and which towns light its horizon. It compares places; it is not a measurement. Step-free notes quote the park's own accessibility pages.

KEEP A LITTLE OF THE NIGHT Save parks and get optional local reminders for promising nights. Keep a private journal with notes and selected photos; each night becomes a star in your own constellation. Export it as a file you keep. Widgets show the best sky among your saved parks.

FOR MORE PEOPLE Nyx is designed for VoiceOver and the largest text sizes. Audio graphs let you hear a month of darkness, haptics can follow the Moon's phase, and a red mode keeps the whole app readable to night-adapted eyes. Spanish is included.

PRIVATE AND OFFLINE Your location, journal and photos stay on your device. Three public services supply data, each with its own switch under Your privacy: park alerts from the National Park Service, and forecasts and smoke from Open-Meteo. They never receive your location. The Moon, twilight, the Milky Way, the park library, the calendar and your journal work without a connection.

PLEASE NOTE Scores are planning estimates. They do not confirm clear skies or open roads. Check current park conditions before you travel.

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