Astrolabe
= Astrolabe
{wiki}
A planispheric <astrolabe> uses a <stereographic projection> of the <celestial sphere> as a physical calculating device. A rotating star map is compared with a latitude-specific plate; a sighting rule measures an object's angular <altitude>. Aligning that measurement with the engraved geometry permits time and celestial-configuration calculations.<Astrolabe by Silke Ackermann>[Epact: components and time-telling procedure]{ref}