Principle of the Astrolabe
1. Cosmic model
1. The astrolabe is based on the two-sphere cosmic model. All stars are fixed on the celestial sphere, with Earth at the center of the celestial sphere.
II Stereographic projection
1. Using stereographic projection, the astrolabe converts information on the celestial sphere into a plane.
First, the south celestial pole is used as the projection point, and the equatorial plane is used as the projection plane. The area north of the Tropic of Capricorn on the celestial sphere can be projected into a circle, which is the edge of climate in the astrolabe.
III Drawing the figure
1. The edge of the climate disk represents the Tropic of Capricorn, and the two concentric circles from the outside to the inside represent the celestial equator and the Tropic of Cancer, and the center of the circle is the North Celestial Pole.
