Answers, and a person to write to.

How do I open the AR view?

Sunlit has four views: Sky, AR, Map and Data. Choose AR. The first time you do, iOS asks for permission to use the camera, because the view draws the paths of the sun and the moon over the live image. Allow it and the camera appears with the paths on top of it.

If you refuse, the AR view still opens, without the camera image behind it. To change your mind later, open the iPhone Settings app, scroll down to Sunlit and switch Camera on.

Hold the phone upright and turn slowly. The amber curve is the path of the sun for the selected date. The moon path, the solstice and equinox reference curves and the galactic plane of the Milky Way are part of Sunlit Pro.

Why does the direction wander, and how do I calibrate it?

The magnetometer in a phone measures the magnetic field of the earth, and it is a weak field. Anything magnetic close by competes with it: a case or wallet with magnets, a MagSafe charger, a car dashboard, a tripod head, a loudspeaker, steel in a wall, a metal desk. This is a property of the hardware, not of the app, and it is the single most common complaint about every augmented reality sun app there is.

Sunlit does not hide it. The AR view carries a chip showing the current heading uncertainty in degrees, at all times, and it turns amber when iOS reports that the compass needs calibrating.

To calibrate: step away from metal and from anything magnetic, take the phone out of a magnetic case, then move it slowly in a figure of eight, turning your wrist as you go, for a few seconds. The figure on the chip should drop.

Two iOS settings matter. In the iPhone Settings app, under Privacy and Security, Location Services, System Services, Compass Calibration should be on. In the same Location Services list, Sunlit should be allowed While Using the App.

Sunlit works in true north, not magnetic north. It reads the attitude of the device in the true north reference frame rather than a raw magnetic heading, and it applies the magnetic declination for your position from a model carried inside the app, so it needs no connection to know the difference. If you compare it against a magnetic compass, the two will disagree by the local declination, which is several degrees in most of the world.

What is free, and what does the purchase unlock?

Free, permanently: today, at your current location, in all four views. That covers the position of the sun, the compass, the path of the sun in AR, sunrise and sunset, civil, nautical and astronomical twilight, golden hour and blue hour, solar noon, day length, shadow length, and the clear sky UV and irradiance models for today. It is not a trial and it does not expire.

Sunlit Pro is a single purchase at 9.99 EUR, shown in your own currency by the App Store. It is not a subscription and there is nothing to cancel. It adds:

• Any date, past or future
• Saved places beyond your current location
• The moon: phase, path, rise, set and calendar
• The Milky Way: galactic centre, galactic plane and visibility windows
• Annual path overlays with the solstice and equinox curves
• A measured horizon profile and obstruction periods
• Eclipses with visibility and obscuration at your place
• Widgets and event notifications
• Export to CSV and image

I bought Sunlit Pro and it is locked again

Open Settings inside Sunlit and tap Restore purchases. That asks Apple whether the Apple Account signed in on this device owns Sunlit Pro, and unlocks it if the answer is yes.

If it stays locked, check that you are signed in with the same Apple Account you bought it with. A phone set up from a different account is the usual reason. A purchase belongs to an Apple Account, not to a device, so there is never anything to pay a second time.

Refunds are handled by Apple rather than by us, at reportaproblem.apple.com.

Are the UV index and the irradiance figures measurements?

No. They are clear sky models, and Sunlit labels them as models wherever they appear. The phone has no ultraviolet sensor, and Sunlit has no weather feed.

The UV index is computed from the altitude of the sun, a total column ozone climatology for your latitude and time of year, your elevation, and the current distance from the earth to the sun. The irradiance figures come from a standard clear sky formula, split into a direct and a diffuse component.

What they tell you is what a cloudless sky would deliver at that moment, at that place. Cloud, haze, dust and pollution are not in the model, so under an overcast sky the real value is far lower. They are a planning tool for light, not a health instrument, and they should not be used for medical or safety decisions.

Does Sunlit work without a connection?

Yes. Every astronomical figure is computed on the device from tables carried inside the app, so aeroplane mode changes nothing about the numbers, anywhere in the world, on any date.

Three optional things use a connection when one is there: searching Apple Maps by name, resolving the time zone of a bare coordinate you dropped on the map, and buying or restoring the purchase. The city list, the magnetic model and every ephemeris table are already on your phone.

How do I change the place or the date?

Both live in the header at the top of the screen and both govern all four views at once. Tap the place to search by name or to pick a saved place; tap the date to move to another day. On the Map view you can also tap anywhere to move the pin, and the rest of the app follows.

Place names come from GeoNames: about 34,000 cities with a coordinate, an elevation and a time zone, carried inside the app, which is why the search works offline. It is used under the Creative Commons Attribution 4.0 licence. If a place you want is not in the list, drop a pin instead. That works anywhere.

Sunlit cannot see where I am

Open the iPhone Settings app, scroll down to Sunlit, tap Location and choose While Using the App. Indoors a first fix can take a few seconds.

You can also refuse location entirely and still use Sunlit: search for a place by name, or drop a pin on the map.

How do I measure my own skyline?

Open the AR view and start the horizon sweep, then turn slowly through a full circle with your skyline in the middle of the frame. Sunlit stores the result as 36 sectors of ten degrees, each holding the apparent altitude of whatever is in the way. You can also type the altitudes in by hand, or leave the horizon flat at zero degrees, which is what almost every other app assumes.

With a profile stored, Sunlit gives you sunrise and sunset over your own skyline as well as over a flat horizon, shows the difference between the two, and lists the periods when the sun is behind an obstruction. The measured horizon is part of Sunlit Pro.

Sunlit gives a different sunrise from another app

Two reasons, and both are deliberate.

First, most apps give you sunrise over a flat horizon at sea level. If you have measured your skyline, Sunlit uses your skyline instead, and shows both figures so that you can see how much the hill or the building costs you.

Second, Sunlit models atmospheric refraction and takes the apparent size of the disc into account, so its times are for the upper edge of the disc meeting your horizon. Small differences of seconds between careful apps are normal and come from these choices rather than from an error.

There is no sunrise for the date I picked

Above the Arctic circle and below the Antarctic circle there are dates on which the sun never rises and dates on which it never sets. Sunlit says polar day or polar night rather than printing a time that does not exist. The event solver reports the absence of an event instead of inventing one, for the moon as well as for the sun.

Widgets and notifications

Sunlit offers a small and a medium home screen widget and two lock screen widgets. Add one the usual way: touch and hold the home screen or the lock screen, then choose Sunlit from the widget list. They refresh at event boundaries rather than on a fixed clock, so a countdown can sit still for a while and then move.

Event notifications are scheduled on your phone by iOS and are delivered locally, with no server involved. If none arrive, open the iPhone Settings app, go to Notifications, find Sunlit and make sure Allow Notifications is on. Widgets and notifications are both part of Sunlit Pro.

How do I get the numbers out?

In the Data view, choose export. Sunlit writes the figures as a CSV file or the chart as an image and hands it to iOS, so you can save it or send it on. Export is part of Sunlit Pro.

Which iPhones, and which languages?

Sunlit runs on iPhone with iOS 17 or later. There is no iPad version and no Apple Watch app. The AR view needs a camera and a magnetometer, which every supported iPhone has.

The app is written in English, German, French, Italian, Spanish, Spanish for Mexico, Dutch, Polish, Japanese and Brazilian Portuguese. Numbers, dates and units follow the conventions of the language you are in.

Something else

Write to levin.schwab@gmx.de and you will get a reply from a person. Bug reports, wrong numbers and requests for a language are all welcome. If you believe a figure is wrong, say which place, which date, which time and which value, and it can be checked against the reference sources directly.