Historical Eclipses and Earth's Rotation

Introduction

Because so many observations of lunar eclipses are preserved on the Late Babylonian astronomical texts, it is necessary to devote two chapters of this book to their discussion. This is a reflection of the great importance of the lunar eclipse records from Babylon in the study of long-term changes in the length of the day. The present chapter is restricted to timed contacts, while in chapter 7 a variety of untimed observations of eclipses of the Moon will be considered.

Most Babylonian lunar eclipse timings are expressed relative to sunrise or sunset, although very occasionally they are referred to moonrise or moonset instead. I have divided these measurements into four categories: (i) those for which only a single contact timing is preserved; (ii) timings of two separate contacts (mainly partial eclipses); (iii) three or four contact timings (total eclipses only); and (iv) timings of eclipse maxima (partial eclipses only). Observations in these categories will be discussed in turn in sections 6.2 through 6.5. In addition, a number of eclipses were also timed in relation to the culmination of certain reference stars (see section 6.6).

Times of the very earliest eclipses (whether observed or predicted) were nearly always quoted with low precision. Between 731 BC (the earliest surviving record, representing a prediction) and just before 600 BC times were almost exclusively expressed to the nearest 10 deg.