Help under a dark sky.

Nyx has four tabs: Tonight, Parks, Plan and Journal. The month for one park and the trip planner are in Plan. The essays are in Settings, under About the sky.

A full cloud forecast counts for about three days ahead. Further out, a half-filled night is an early look: the forecast is eased toward the place's usual clouds for that month. A hollow night has no forecast yet and uses the usual clouds alone, so its score can change when a forecast arrives. Pull down to refresh when you have a connection, and check that Cloud forecasts is on under Settings → Your privacy.

The four parts add up, then the weakest one can cap the total: heavy cloud, a bright sky glow, smoke or short hours of true darkness. The line under the score names the cap that applies.

Nyx could not get current alerts for a US national park. Use the link to the park's current conditions on nps.gov, or contact the park before traveling.

Widen the radius or choose a different starting point. The radius is a straight line, not driving distance.

Tonight asks where you start from. Choose Near me to use your location while you use Nyx, or choose a starting point: any of more than 31,500 towns and cities, a park, or a spot you saved. The towns at the park gates are there too, such as Moab, Springdale, Estes Park and West Yellowstone. Location is optional, and your choice stays on your device.

Nyx lists about 3,400 national parks and certified dark-sky places in 172 countries, from Wikidata, each scored night by night. Their sky glow comes from satellite night lights and their usual clouds from ten years of weather records, both estimates. Nyx has no closure information for them: "Nyx can't check closures here" means exactly that, and the Park website link opens the park's own site. Forecast comparison between models and the smoke forecast are for the US national parks only.

Save a spot of your own from Parks or from "Where do you start from?": where you stand, a pair of coordinates or a town. It is scored like a park and kept on your device. Its cloud forecast is asked for with its position rounded to about 11 km (7 miles); turn off "Clouds at your saved spots" in Settings → Your privacy and the spot uses its usual clouds instead.

The forecast service asked Nyx to wait, usually because many requests came from the same network. Nyx shows the last forecast it has, then each place's usual clouds, and asks again after the wait, even across a restart. Settings → Your privacy → Advanced shows how many forecast requests this device made today. "Up to date" after a pull means the forecast is recent enough that asking again would not change it.

In every App Store storefront except mainland China and the European Union.

Nyx speaks English, Spanish, German, French and Japanese, following your device's language. The translations are drafts that native speakers will review; if a phrase reads wrong, please write.

On a park's page, The place lists the park's campgrounds from the National Park Service. Reservation links open only Recreation.gov or nps.gov. The list is asked for all 63 parks at once, at most once a week, and not in Low Data Mode.

At the foot of Tonight, Nyx works out the Moon, true darkness, planets, meteor showers and eclipses for your starting point, on your device, with no request. It estimates the sky brightness there from satellite night lights, asks for no cloud forecast and gives no score: check your local forecast for clouds.

On a park's night, Follow this night puts the night on your Lock Screen as a Live Activity. It starts on its own about 30 minutes before sunset, and no server is involved.

Save a park or spot, or follow a place, and turn on reminders in Settings. Only nights scoring 90 or more, up to five days ahead and with a recent, full cloud forecast, qualify, and at most one a week for each park. Reminders are recalculated whenever Nyx opens and, when iOS allows, about every six hours in the background.

In Alaska's summer the Sun never sinks 18° below the horizon, so true darkness never arrives. Nyx caps those nights below 40.

Turn it on with the flashlight button at the top left of every tab, in Settings, or from Control Center. Lower your screen brightness too; outside field mode, Nyx does not change it for you.

Closed, Nyx works like it does on any iPhone, with its tabs and buttons in the side bar; when there is no room, Night vision is the last to move into the overflow menu. Open flat, Tonight, a park and the Journal show two columns, and Parks shows the list beside the park. Half open like a book, the columns meet at the fold. In field mode, "Where to look" follows the phone only when it is open flat or closed; part way open, it asks you to open it flat.

Turn your iPhone and Nyx turns with it. In field mode, the night sits beside "Where to look". If the screen does not turn, check Portrait Orientation Lock in Control Center.

The medium and large Tonight widgets have previous and next buttons beside the night they show. Tap one to step through the week; a tap on the night itself opens the park on that night. Widgets cannot check closures for you, so open the park before you travel.

Only tonight and nights that have passed can be recorded. On iPad, drag a night from the calendar onto the Journal, for example onto its row in the sidebar, to start an entry for it. On iPhone and iPad, touch and hold a night, then choose Record this night. VoiceOver offers the same action on each night.

Entries and photos stay on your iPhone or iPad. Back up your device with Apple's settings; Nyx has no cloud sync or account recovery. To move a journal to another device, use Export in the Journal tab and open the file on the other device. Nyx asks before it imports a journal file, and removes the location from its photos.

When Nyx runs in a language other than English, a Translate button under park alerts and ranger programs opens Apple's translation, which runs on your device.

When your iPhone or iPad uses Assistive Access, Nyx shows one answer in large type: tonight's darkest park within reach, and your saved parks, each with one word for the night, the Moon, when true darkness begins and any closure.

In a few US states, the law asks apps to check the age range of new accounts. Where iOS says this applies to your account, it may show its own age range sheet once. Nyx keeps nothing from it and nothing in Nyx depends on the answer.

With the largest accessibility text sizes, Parks shows its search field in the page, under its title, instead of in the navigation bar.

The watch makes no network requests. Its cloud forecasts come from Nyx on your paired iPhone: open Nyx on the iPhone with a connection, and the watch updates. Until then, the watch scores each night with the park's usual clouds and says so.

When the three forecast models disagree about a night's clouds, the watch shows their range beside the score, as the dial on your iPhone does. The range comes from Nyx on your iPhone with the forecasts; the watch shows it only on nights it scores from a full forecast.

With the Automatic palette, the watch turns red from dusk to dawn at the park on Tonight. Choose another palette in Nyx on the watch, or use the Red light control.

The watch shows the parks, places and spots you follow on your iPhone.

Nyx on Apple Vision Pro covers the 63 US national parks; places around the world and saved spots are on iPhone and iPad. Choose a park in the window, then "Stand under this sky". "Leave the sky" closes it. The clock at the bottom of the window steps nights and moves through the hours, and the sky follows.

Nyx on Vision Pro uses the cloud forecast when it has one and each park's usual clouds for the month otherwise (or when you switch forecasts off in Your privacy). Smoke and haze are not counted on Vision Pro, and a line under the score says so; on smoky days, check Nyx on iPhone. For park alerts and field mode, use Nyx on iPhone or iPad.

The sky is computed for the park and night you choose, with south ahead of you, where the Milky Way, Moon and planets cross. It is not turned to your room's real directions; a plaque at your feet says so. When Nyx has a forecast for that night, clouds follow it, and their shapes are illustrative.

Tap a planet, a bright star, the Moon or the Milky Way core to see its name, its height and its direction. Constellations in the window toolbar shows or hides the figures. Drag across the sky to turn the night by hand.

Open it from the window toolbar. It is lit at that night's phase; drag to turn it, and it turns back to the face we always see.