Stellar Tour — privacy policy

Effective 10 September 2026. Stellar Tour is written and published by Aaron Day. This policy covers the Android app com.incalculable.stellar_tour, sold on Google Play, and the iPhone and iPad app of the same name. Questions go to cosmologyapp@gmail.com.

The short version. Stellar Tour has no account, no analytics, no advertising and no tracking of any kind. There is no Stellar Tour server: we hold no data about you anywhere, because we have nowhere to hold it. What the app needs to draw your sky stays on your phone. Three outside services see a request when you use the feature that needs them — a weather service, a satellite-orbit archive and an astronomy picture archive — and Google Play handles purchases and downloads. That is the whole of it.

Your location. The app asks for your location when it starts, so it can work out where the Sun, Moon, planets, stars and satellites are from where you stand. You can refuse, and the app still works: you then set the observing place by hand in the place picker, or the sky is drawn for a default site. The fix itself is used on the device and is not sent to us. A place you set by hand, the place the sky alerts were last planned for, and the place name the home-screen widget shows are kept in the app's own settings on the phone, and go when the app goes.

Two things send your coordinates off the phone, both in the service of something you asked for:

The cloud forecast. When you open Sky Forecast, or the Tonight briefing's cloud row, the app asks a weather service for the hourly forecast at your observing site, and your coordinates go with the request — nothing else does, no identifier of you or your phone. The service this version uses is Open-Meteo (api.open-meteo.com). If that changes, this policy names the new one. The forecast comes back and is cached on the phone for a few hours.
The name of the place. To show a place name rather than a pair of numbers — in the widget, and in the place picker when you search for a town by name — the app uses Android's own geocoding service. That means the coordinates, or the text you typed, are handled by the service your phone uses for geocoding, which on most phones is Google's. The iPhone version does the same thing through Apple's geocoder. The app does not send your coordinates anywhere else, and it asks only when it needs a name it does not already have.

The camera. The augmented-reality view shows the live camera picture behind the sky. The frames are handed to the screen and thrown away: nothing is recorded, stored or transmitted. The app asks for the camera permission only when you switch the AR view on, never at launch, and works without it. If you save a screenshot while the AR view is up, the picture you save contains what the camera saw, because that is what was on the screen.

Motion and the compass. The app reads the phone's rotation sensors, which need no permission, so the sky follows where you point the phone. This never leaves the device.

Photos. If you choose a photo as a custom Milky Way background, the app copies that one picture into its own private storage so it survives a restart. It reads no other photo, and it needs no photo-library permission to do it: Android's own photo picker hands over the one file you chose. When you save a picture of the sky, the app writes it to a "Stellar Tour" album in your gallery, where it is yours to keep, move or delete.

Purchases. Cosmic Expansion and the Upgrade are one-time purchases made through Google Play. Google takes the payment and holds your payment details; the app is told only whether the purchase belongs to the Google account on the phone, and remembers that as two yes-or-no flags in its own settings. We never see your card, your name or your Google account.

Sky alerts. Reminders for eclipses, meteor showers, conjunctions and satellite passes are computed on the phone and posted by the phone's own alarm clock. Nothing is sent to a notification server, and no reminder leaves the device. The app asks for the notification permission only when you switch a category of alert on.

What the app downloads. Its picture packs come from Google Play, which sees the download as it sees any download from the store. Satellite orbital elements come from Celestrak (celestrak.org), and they describe the satellite, not you. James Webb Space Telescope pictures come from the ESA/Webb archive (cdn.esawebb.org) when you open a page that shows one. A chapter video plays inside the app through YouTube's player (www.youtube.com): YouTube sees the request as it would any embedded video, and may set its own cookies in the app's browser component, which are removed when the app is. Every one of these requests is made over HTTPS, and, like any web request, shows the server your device's IP address for the length of the request. We send them nothing else about you and learn nothing about you from them.

Crash records. If the app crashes, stops responding, or is killed by the phone for using too much memory, it writes a small record — the time, the app and Android version, the phone's model, and the technical trace — into its own folder on the phone, so that it can be sent to us by hand if you want help. Nothing is uploaded, there is no crash-reporting service in the app, and the records contain nothing about you. Separately, and outside the app's control, Android itself reports crashes of apps installed from Google Play to Google, where we see only anonymous counts.

Children. Stellar Tour collects no personal data from anyone, of any age. It has Kid Mode, which rewrites the tour for explorers aged five to seven and is a setting a grown-up switches on; turning it on changes the words and the colours, not what the app does with data. The app has no ads, no social features, no chat, no user accounts and no links out to a browser other than the ones described above. It is not directed at children under 13, and it asks nothing of a child that it does not ask of anyone else: nothing.

Your rights. There is no data about you for us to show, correct, export or delete, because none of it reaches us. Everything the app stores — your settings, your saved constellations and searches, the place you chose, the cached forecast, the cached pictures, the crash records — is inside the app's own storage on your phone and is deleted when you uninstall the app. Pictures you saved to your gallery are yours and stay there. If you want the app's data gone without uninstalling, Android's Settings → Apps → Stellar Tour → Storage → Clear data removes all of it. For anything else, write to cosmologyapp@gmail.com and we will answer.

Third parties, in one list. Google Play (purchases, downloads, and the optional rating card); the weather service this version of the app uses, Open-Meteo; Android's geocoding service, for place names; Celestrak, for satellite orbits; the ESA/Webb archive, for pictures; YouTube, when you play a video. None of them is given anything about you beyond what the request itself carries, and none of them pays us or receives anything from us.

Changes. When this policy changes, the new version is published at this address with a new effective date.