Privacy Policy

Last updated 1 September 2026

Sidereo is an astronomy app for iPhone. It has no accounts and no sign-in, so there is no user record of you anywhere, and nothing you do in the app is reported back to us. This page describes exactly what stays on your phone and the three requests that leave it.

What we collect

Nothing about you. There is no database, no analytics and no advertising SDK anywhere in the app, and nothing measures what you tap or follows you into other apps and websites.

We do run one small server: sidereo.app serves this website and a two read-only endpoints that mirror public comet and satellite orbital elements, so the app can fetch a current list without every phone hammering the original catalogues. It has no database and no account system, it never receives your location, and it returns the same data to everyone who asks. Like any host, Cloudflare — which runs it — sees the IP address a request arrives from.

What stays on your device

Your favourites, observation logs, discovered-object list, equipment, settings and any photos taken in the app are stored locally using Apple's on-device SwiftData framework. They are not uploaded anywhere. Deleting the app deletes them.

Photos you choose to analyse, and any in-app guidance based on them, are processed on the device.

Requests that leave your device

Sidereo computes astronomical positions locally and works fully offline. A small number of optional features fetch live data from third parties. Each is listed below with exactly what it receives. We have no relationship with these providers, receive nothing back from them, and none of these requests carries an account, identifier or device ID.

As with any internet request, these providers necessarily see the IP address the request comes from, and each has its own privacy policy. Every one of these features is optional: with no network connection, Sidereo still computes the sky, and every object ships with its own offline description.

Location

Sidereo uses your location to work out what is above you right now. It is used on the device for every astronomical calculation, and it is not stored by us or transmitted to us.

The one exception is Live Weather, and it is deliberately blunt: before that request is made, your coordinate is rounded to two decimal places — about a kilometre. That is far coarser than any forecast model's own grid, so it costs the forecast nothing, and it is not enough to place you.

If you would rather it never happened at all, turn Live Weather off in Settings. Then no request carrying a location is made, and the Tonight tab scores the sky from astronomy alone. Setting a manual location instead of granting GPS access does not prevent the request — the manual coordinate is sent in exactly the same way, blunted in exactly the same way. Only the switch stops it.

Camera, motion and photos

The camera is used to draw the sky over the live view and to frame astrophotography shots. Motion sensors are used to know which way the phone is pointing. Photo library access is used to save what you create and, if you choose, to read a photo you ask the app to analyse. None of this data leaves the device.

Purchases

Subscriptions are handled entirely by Apple through StoreKit. Sidereo never sees or stores your payment details. Apple's own privacy policy governs that transaction.

Children

Sidereo is not directed at children under 13 and collects no personal information from anyone.

Changes

If this policy changes, the date at the top of this page changes with it, and the previous version is replaced here. There is no mailing list to notify, because we hold no addresses.

Contact

Questions about privacy: support@sidereo.app.