Chapter 0

Introduction

A total solar eclipse is about the finest thing a person can see and experience with their own eyes. Everyone should make sure they get to see one at least once in their life. That means travelling to the path of totality, because staying put usually means waiting longer than a human lifetime. In Finland the next total eclipse will be seen in 2126.

Partial solar eclipses and lunar eclipses can be seen more often, and without leaving home. The experience is nowhere near that of a total solar eclipse, but for anyone interested in the sky they can still be interesting, and sometimes genuinely cool looking.

Predicting eclipses is nowadays largely a solved problem. The times and places of future eclipses have been worked out for a very long time now. Long ago they were predicted with who knows what clay tablets, later with purpose-built mechanical machines, a little after that with slide rules and mile-long paper strips, and finally, of course, with computers.

For a normal sane person, understanding how eclipses are predicted is of no use whatsoever. So, this site covers the subject in very great detail!

The text is written so that the basics of eclipses, astronomy and mathematics are not explained from the ground up. The aim is still to keep the content such that there is something interesting to browse with less background too, if nothing else then at least fine pictures and animations.

Nor is every calculation derived from scratch or with all its intermediate steps. You will find that in the reference material. The formulas shown are above all the ones someone willing would need for implementing the calculations themselves, the ones that matter for understanding the thing, or the ones that are somehow otherwise neat or interesting.

The calculation of the positions of the Earth, Sun, and Moon is not described in detail. Instead, it is assumed that these positions can be readily computed with suitable tools, particularly Skyfield, in this case.

The main sources have been the Explanatory Supplement, Jean Meeus’s excellent books, and of course Fred Espenak’s life’s work.