Plan the light.
Record the sky.

Asterfold is a sunset field studio for iPhone and iPad with three connected parts. The Light Path Studio calculates the Sun's path, bearing, altitude, golden hour and blue hour for any place, saved viewpoint and date. The Viewpoint Planner saves the exact spots you watch from, with the direction you face, finds the dates when the Sun sets inside your view and plans sessions. The Field Journal records what each sunset really looked like and compares it with the forecast saved before the event. Tonight also rates the sunset, stars and sunrise from the cloud forecast.

A sky dome showing the Sun's path for the day, coloured by golden hour, blue hour and twilight, with the year's sunset range on the rim. Drag through the day to read altitude, bearing and shadow length, or jump to the solstices. It is calculated on your device, works offline, and assumes a flat horizon, which it says on screen.

Save a spot by GPS, town search or coordinates, then open Aim your view. Drag the first-person horizon left or right like turning your head, tap a sun line such as the year's most northerly sunset, or point your iPhone at the view and let the compass follow. Pick a lens (14 mm to 200 mm, or the phone's main camera) to set the frame width; green viewfinder corners and monthly sun dots show what will be in your shot as you aim. Asterfold lists the dates in the coming year when the Sun sets or rises inside that view, the next seven sunsets against your frame, and lets you plan a session with a light window, composition, gear, a reminder and a short checklist. Free keeps two viewpoints; Plus keeps unlimited.

Colorful sunsets need high or mid-level clouds to catch the light and a clear path for the light to reach them. Asterfold reads the forecast cloud layers (low, mid and high), fog and rain above you, and also the ordinary point forecast at two places 60 km and 180 km along the setting Sun's bearing, where low cloud can cut the light off. The app shows the reason with every rating. The rating is a rule-of-thumb score: it has not been validated against observed sunsets and is not a probability.

At sunset the Sun's light reaches your clouds almost sideways, after travelling a few hundred kilometres under them. Asterfold fetches MET Norway's standard point forecast at two places on that line, 60 km and 180 km toward the setting (or rising) Sun, and shows them next to your own spot as a cross-section. These are two samples of the forecast, not a model of every cloud along the line, and nearby hills or buildings aren't included.

After a sunset you rate what you saw in two taps and can add colours, clouds, the Sun, a note and an optional photo kept privately on your device. Each check-in is compared with the forecast saved before the event, never revised afterwards. After three check-ins nearby, ratings adjust for clear, high-cloud and cloudy evenings in small steps capped at 25 points, and once you have three at one viewpoint they use only that viewpoint. Sunsets you log elsewhere are kept as observation-only notes.

Cloud, rain and fog forecasts come from the Norwegian Meteorological Institute (MET Norway) and reach about nine days ahead. Sun, Moon and planet times are calculated on your device.

Yes. The Light Path Studio, two viewpoints with alignments and plans, the Field Journal, check-ins and tuning, Tonight's ratings and light path, all the times, golden hour reminders, the next three evenings, 45 days of sky events and the Sky Log are free. Asterfold Plus adds unlimited viewpoints, smart alerts, the full 10-day outlook and a full year of events.

No account, no ads, no analytics. Viewpoints, plans, journal entries and kept photos stay on your device and are never uploaded. Only a position rounded to about 1 km is sent to MET Norway to fetch cloud forecasts.

Yes. The Stars rating combines forecast cloud during real darkness with moonlight, and the app shows the clearest stretch of the night and the moon-free hours. It doesn't include light pollution, so dark rural sites will do better than the number suggests.

No. Forecasts change and local conditions vary. The ratings are an unvalidated rule-of-thumb estimate to help you decide when it's worth stepping outside; they are not a probability and their accuracy has not been measured.