Introduction

Arab observations of solar and lunar eclipses which are of value in the study of the Earth's past rotation originate exclusively from the medieval period. These records are found in two main sources: (i) chronicles, and (ii) compendia on astronomy. As might be expected, the observations reported in chronicles are essentially qualitative; measurements of any kind are fairly rare. Eclipses and other celestial phenomena (such as bright comets and meteor showers) were mainly noted on account of their spectacular nature. Yet chronicles contain some important astronomical records. The present chapter will be devoted to eclipses described in these works. Arab compendia on astronomy contain many careful measurements of the times of the various phases for both solar and lunar eclipses. These observations will be discussed in chapter 13.

The Arabic names for the Moon and Sun are respectively al-Qamar and al-Shams. In general, medieval Arab chronicles use the term khusuf al-Qamar for an eclipse of the Moon and kusuf al-Shams for an eclipse of the Sun. These designations are still in use today, both among astronomers and the general public. However, medieval Muslim astronomers mostly used kusuf for both types of eclipse, adding the appropriate term for the Moon or Sun. The word khusuf means ‘sinking’, but in describing a lunar eclipse it came to mean a failing of the Moon's light. By contrast, kusuf means a ‘cut’ – i.e. in the solar (or lunar) limb.