Some Problems on the Orthographic Projection of the Sphere

Abstract

First Paragraph When a sphere is orthographically projected upon a plane, the location of a point on its surface and of its projection upon the plane is determined by certain systems of coordinates, the interrelation of which it is the object of this article to examine. In order the better to fix our ideas, let us take the terrestrial sphere as seen from a star. The plane of projection will then be the background of the sky. As projections upon parallel planes are identical, let us for the sake of convenience pass this plane through the center of the sphere and call it the fundamental plane. Let the elevation of the north end of the Earth’s axis above the plane of projection be called 8, an angle evidently equal to the star’s declination.