Re: The Trilogy of Sanity

https://pseudoastro.wordpress.com/2011/06/28/the-magical-hyperbolic-tetrahedral-geometry-of-19-5%C2%B0-latitude/ 
 
Take a tetrahedron (4-sided solid made of four equilateral triangles) 
and put it in a sphere such that each point of the pyramid touches the 
inside surface of the sphere. Draw a straight line through the center 
of the sphere such that one end of the line intersects a point of the 
pyramid; think of this line as the polar axis, and now orient it in 
your mind so that the line that goes through the pyramid point is 
down. Now draw a line around the circle’s equator. Now, if you take 
the angle between the equator, the center of the sphere, and one of 
the three non-pole points of the pyramid, you get 19.5°.