Working it out…
Your location is kept in this browser only. Nothing is sent anywhere.
Your location, display settings and night mode are saved in this browser only. Nothing is sent anywhere.
Set your location, then tap Point at the sky on your phone and hold it up: the map turns with you and names what's in front of the camera. Search for a star, planet or constellation and follow the arrow. Turn on Night mode (red on black) and give your eyes 15 to 20 minutes to adjust; bright white screens undo that in seconds.
Phones find north with a small magnetometer, which is thrown off by metal, magnets, cars, phone cases and nearby electronics. If the map doesn't line up with what you see, move away from metal and wave the phone in a slow figure 8, or drag sideways to nudge the view until a star you know lines up. The map corrects for the difference between magnetic and true north using the World Magnetic Model.
Stars are the 9,096 in the Yale Bright Star Catalogue (5th edition), everything down to about magnitude 6.5, moved to today's date for precession and proper motion. Star names are the IAU's official list. Constellation figures and boundaries come from Olaf Frohn's d3-celestial (BSD licence). The Sun, Moon and planets are worked out with Don Cross's Astronomy Engine (MIT licence), checked against NASA JPL's Horizons to within an arcminute. Rise and set times allow for refraction; distances come from the catalogue's parallaxes and are rough for distant stars. The Milky Way option is a rough band along the galactic plane, not a traced outline. Sources and licences.
No. Everything is worked out in your browser. If you tap Use my location, your browser gives the position to this page only; it's rounded to about a kilometre and saved on your device. The motion sensors are only read while Point at the sky is on. Export, import or delete your saved settings under Your data.