eclipse Medieval Islamicastronomy

Like their Christian counterparts, medieval Islamic chroniclers recorded a number of detailed and often vivid descriptions of eclipses. Usually the exact date of occurrence is given (on the lunar calendar). A graphic narrative of the total solar eclipse of June 20, ad 1061, was recorded by the Baghdad annalist Ibn al-Jawzī, who wrote approximately a century after the event:

On Wednesday, when two nights remained to the completion of the month Jumādā al-Ūlā [in ah 453], two hours after daybreak, the Sun was eclipsed totally. There was darkness and the birds fell whilst flying. The astrologers claimed that one-sixth of the Sun should have remained [uneclipsed] but nothing of it did so. The Sun reappeared after four hours and a fraction. The eclipse was not in the whole of the Sun in places other than Baghdad and its provinces.

The date corresponds exactly to June 20, ad 1061, on the morning of which there was a total eclipse of the Sun visible in Baghdad. The duration of totality is much exaggerated, but this is common in medieval accounts of eclipses. The phenomenon of birds falling from the sky at the onset of the total phase was also noticed in Europe during several eclipses in the Middle Ages.

Two independent accounts of the total solar eclipse of ad 1176 are recorded in contemporary Arab history. Ibn al-Athīr, who was aged 16 at the time, described the event as follows:

In this year [ah 571] the Sun was eclipsed totally and the Earth was in darkness so that it was like a dark night and the stars appeared. That was the forenoon of Friday the 29th of the month Ramaḍān at Jazīrat Ibn ʿUmar, when I was young and in the company of my arithmetic teacher. When I saw it I was very much afraid; I held on to him and my heart was strengthened. My teacher was learned about the stars and told me, “Now, you will see that all of this will go away,” and it went quickly.

The date of the eclipse is given correctly, apart from the weekday (actually Sunday), and is equivalent to April 11, ad 1176. Calculation shows that the whole of the Sun would have been obscured over a wide region around Jazīrat Ibn ʿUmar (now Cizre, Turkey). Farther south, totality was also witnessed by the Muslim leader Saladin and his army while crossing the Orontes River near Ḥamāh (in present-day Syria). The chronicler ʿImād al-Dīn, who was with Saladin at the time, noted that “the Sun was eclipsed and it became dark in the daytime. People were frightened and stars appeared.” As it happens, ʿImād al-Dīn dates the event one year too early (ah 570); the only large eclipse visible in this region for several years was that of ad 1176.

Lunar and solar eclipses are fairly frequently visible on Earth’s surface 15 days apart, and from time to time such a pair of eclipses may be seen from one and the same location. Such was the case in the summer of ad 1433, but this occurrence caused some surprise to the contemporary Cairo chronicler al-Maqrīzī:

On Wednesday the 28th of Shawwāl [i.e., June 17], the Sun was eclipsed by about two-thirds in the sign of Cancer more than one hour after the afternoon prayer. The eclipse cleared at sunset. During the eclipse there was darkness and some stars appeared.…On Friday night the 14th of Dhū ʾl-Qaʿda [July 3], most of the Moon was eclipsed. It rose eclipsed from the eastern horizon. The eclipse cleared in the time of the nightfall prayer. This is a rarity—the occurrence of a lunar eclipse 15 days after a solar eclipse.

The description of the loss of daylight produced by the solar eclipse is much exaggerated, but otherwise the account is fairly careful.

Medieval Arab astronomers carefully timed the various phases of eclipses by measuring the altitude of the Sun (in the case of a solar eclipse) or of the Moon or a bright star (for a lunar obscuration). These altitude measurements were later converted to local time. For instance, the lunar eclipse of April 22, ! 981, was recorded by the Cairo astronomer Ibn Yūnus:

This lunar eclipse was in the month of Shawwāl in the year 370 of al-Hijrah [i.e., 370 ah] on the night whose morning was Friday.…We gathered to observe this eclipse at Al-Qarāfah [a district of Cairo] in the Mosque of Ibn Nasr al-Maghribī. We perceived the beginning of this eclipse when the altitude of the Moon was approximately 21 deg. About one-quarter of the Moon’s diameter was eclipsed. The Moon cleared completely when about ¹/₄ of an hour remained to sunrise.

As seen from Cairo, the Moon would reach an altitude of 21° at 3:32 am. The time when the eclipse ended corresponds to 5:09 am.

Certain Arab astronomers used timings of the same lunar eclipse at two separate locations to determine the difference in longitude between the two places. Plans were made for joint observation at the two places based on prediction of the eclipse. For instance, from timings of the lunar eclipse of July 5, ad 1004, at Ghazna (now Ghaznī, Afghanistan) and Jurjāniyyah (now Kunya-Urgench, Turkm.), the Persian scholar al-Bīrūnī estimated the longitude difference between the two cities as 10.2°. The correct figure is 9.3°. This technique was later widely adopted in Europe.