StarFix Sextant

StarFix Sextant works out where you are by photographing the night sky. No GPS. No network. No compass. Everything is computed on your iPhone, and nothing ever leaves it. HOW IT WORKS Aim the camera at a clear patch of sky and keep the phone still. StarFix Sextant stacks a burst of frames, finds the point sources, and identifies the star field against a catalogue stored on the device — starting from no idea where on Earth you are. The stars alone do not tell you your position. They only tell the phone how it is oriented in space. What carries the position is gravity: expressed in the frame of the stars, your local vertical points at one spot on the celestial sphere. Its declination is your latitude, its right ascension your local sidereal time. Subtract Greenwich sidereal time and you have your longitude. WHAT ACCURACY TO EXPECT 5 to 15 km in good conditions. 25 to 60 km in ordinary…