Introduction

The eclipse observations made by medieval Arab astronomers are among the most accurate and reliable data from the whole of the pre-telescopic period. Careful records of both solar and lunar eclipses are contained in a number of compendia – some known as zijes (astronomical handbooks containing various tables along with explanatory text). These include measurements of the times of occurrence and other details such as magnitude estimates. Although the main emphasis in this chapter will be on timed data, solar magnitude estimates and horizon observations of eclipses will also be considered.

Many of the observations discussed below were investigated by Newcomb (1878) and Newton (1970). However, these authors relied on published translations which sometimes contained significant errors, while their own interpretations are occasionally suspect. Furthermore, in neither case was a direct solution made for ΔT.

Sources of data

Most of the accessible eclipse observations by medieval Arab astronomers are contained in a single treatise – the zij compiled by the great Cairo astronomer Ibn Yunus, who died in AD 1009 (his date of birth is unknown). A few eclipses are also recorded in works by al-Battani (who lived between AD 850 and 929) and al-Biruni (AD 973–1048).

Ibn Yunus cites reports of some thirty solar and lunar eclipses from between AD 829 and 1004. His treatise, dedicated to Caliph al-Hakim, is entitled al-Zij al-Kabir al-Hakimi.