Engineering
Astrolabe: a mechanical sky computer
Sight a star, measure its altitude and rotate a brass sky map to recover local sidereal time. Compare a matching latitude plate with the wrong plate.
Try this
Choose a visible star. Set the plate to your latitude, measure its altitude, then solve for the rete position. Try a wrong latitude or a sighting error. Rising and setting give different answers.
The model and its limits
Northern planispheric teaching instrument. Fixed mean star positions; no precession or refraction. The result is local sidereal time, not civil clock time. The rear sight is displayed beside the front.
Equations used in the module
Equations H = 15° (LST - RA) sin h = sin φ sin δ + cos φ cos δ cos H x = -cos δ sin H / (1 + sin δ) y = cos δ cos H / (1 + sin δ)
