13 - Time and Astronomy

Summary

Ask my friend l'Abbé Sallier to recommend to you some meagre philomath, to teach youa little geometry and astronomy; not enough to absorb your attention, and puzzle your intellects, but only enough, not to be grossly ignorant of either. I have of late been a sort of an astronome malgré moy, by bringing last Monday, into the house of Lords, a bill for reforming our present Calendar, and taking the New Style. Upon which occasion I was obliged to talk some astronomical jargon, of which I did not understand one word, but got it by heart, and spoke it by rote from a master. I wished that I had known a little more of it myself; and so much I would have you know.

—Letter from Philip Dormer Stanhope (Fourth Earl of Chesterfield) to his son, February 28, 1751 C.E.(Julian)

The calendars in the second part of this book are based on accurate astronomical calculations. This chapter defines the essential astronomical terms and describes the necessary astronomical functions. Fuller treatment can be found in the references—an especially readable discussion is given in [9].

We begin with an explanation of how positions of locations on Earth and of heavenly bodies are specified, followed by an examination of the notion of time itself.