🧭 Astrolabe: Stereographic Projection, Altitude-Azimuth and Telling Time from a Star

A brass planispheric astrolabe built on live spherical astronomy: stereographic projection from the south celestial pole turns altitude and azimuth into exact circles; sight a star with the alidade, set the rete and read the solar time, checked against sin h = sin φ sin δ + cos φ cos δ cos H.