## Heavenly Mathematics: The Forgotten Art of Spherical Trigonometry

This is a very interesting book. The author is passionate about the subject and has a passion for geometric explanations.

The analogies to plane trigonometry are explored. The role of Islamic, Indian as well as ancient Greek mathematics was instructive. The motivations for understanding the heavens and the calculational aspects made the geometry comprehensible with the simplest of tools. The development of table for trigonometric tables and the value of logarithms in the periods before calculating machines was enjoyable. Further, the exploration of the regular polyhedra, the proof of Euler’s formula (F+V-E=2 for complex polyhedron), the proof of number of regular polyhedra and explorations of area and volume were enjoyable diversions.

I found the later chapters difficult. This almost certainly reflects my lack of geometric insight and education (a long term deficit).