Literary and Historical References

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The following subsections address some aspects of how eclipses were regarded by the great ancient civilizations. When reading these accounts of long-gone people who grappled with the implications of startling and portentous events in the sky, one cannot help but be struck by the immediacy of their emotions, and one must also admire the beginnings of astronomy, of humanity's understanding, however dimly, of its place in the universe.

Chinese

According to long-established tradition, the history of astronomy in ancient China can be traced back before 2000 BCE. The earliest relics that are of astronomical significance date from nearly a millennium later, however. The Anyang oracle bones (inscribed turtle shells, ox bones, and so forth) of the latter part of the Shang dynasty (c. 1600-1046 BCE), which were uncovered near Anyang in northeastern China, record several eclipses of both the Sun and the Moon. The following report is an example:

On day guiyou [the 10th day of the 60-day cycle], it was inquired [by divination]: "The Sun was eclipsed in the evening; is it good?" On day guiyou it was inquired: "The Sun was eclipsed in the evening; is it bad?"

The above text provides clear evidence that eclipses were regarded as omens at this early period (as is true of other celestial phenomena). Such a belief was extremely prevalent in China during later centuries. The term translated here as "eclipse" (shi) is the same as the word for "eat." Evidently the Shang people thought that a monster actually devoured the Sun or Moon during an eclipse. Not until many centuries later was the true explanation known, but by then the use of the term shi was firmly established to describe eclipses, and so it remained throughout Chinese history. The oracle-bone text, translated above, twice gives the day of the sexagenary cycle; this cycle, which was independent of any astronomical parameter, continued in use (seemingly without interruption) until modern times. Nevertheless, as the year in which an eclipse occurred is never mentioned on the preserved oracle bones (many of which are mere fragments), dating of these observations by astronomical calculation has proved extremely difficult. In general, Shang chronology is still very uncertain.

The Shijing ("Classic of Poetry") contains a lamentation occasioned by an eclipse of the Moon followed by an eclipse of the Sun. The text, dating from the 8th century BCE, may be translated:

The Sun was eclipsed, we found it greatly ominous . . . that this Moon is eclipsed is but an ordinary matter; but that this Sun is eclipsed—wherein lies the evil?

The different attitudes toward solar and lunar eclipses at this time is interesting. Throughout the subsequent 1,000 years or so, lunar eclipses were hardly ever reported in China—in marked contrast to solar obscurations, which were systematically observed during much of this period. The earliest of these observations are recorded in a chronicle of the Chinese state of Lu (now in Shandong Province), the birthplace of Confucius. This work, known as the Chunqiu ("Spring and Autumn [Annals]"), lists many solar eclipses between 722 and 481 BCE. On three occasions the Chunqiu describes eclipse ceremonies in which drums were beaten and oxen were sacrificed. Further, three eclipses (occurring in 709, 601, and 549 BCE) were described as total. The earliest of these, that of July 17, 709 BCE, is recorded as follows:

Third year of Duke Huan, 7th month, day renchen [the 29th day of the cycle], the first day of the month. The Sun was eclipsed and it was total.

This is the earliest known record of a total solar eclipse from any civilization. Computation shows that this eclipse was indeed total at Qufu, the Lu capital.

From about 200 BCE (following the unification of China into a single empire), a wide variety of celestial phenomena began to be noted on a regular basis. Summaries of these records are found in astronomical treatises contained in the official histories. In many instances, a report is accompanied by a detailed astrological prognostication. For example, the Houhanshu ("History of the Later Han Dynasty") contains the following account under a year corresponding to 119-120 CE:

On the day wuwu [the 55th cyclical day], the 1st day of the 12th lunar month, the Sun was eclipsed; it was almost complete. On Earth it became like evening. It was 11 deg in the constellation of the Maid. The woman ruler [i.e., the empress dowager] showed aversion to it. Two years and three months later, Deng, the empress dowager, died.

The date of this eclipse is equivalent to Jan. 18, 120 CE. On this exact day there

Chinese text from an astronomical treatise contained in the Houhanshu ("History of the Later Han Dynasty"), in which two solar eclipses, in 118 and 120 CE, are recorded. The second account, of the eclipse of Jan. 18,120, notes (in the large characters) that the eclipse "was almost complete. On the Earth it became like evening." The account adds that the empress dowager was upset by it, and two years and three months later she died. F. Richard Stephenson occurred an eclipse of the Sun that was very large in China. The above-cited text is particularly interesting because it clearly describes an obscuration of the Sun, which, though causing dusk conditions, was not quite total where it was seen. With regard to the accompanying prognostication, it should be pointed out that a delay of two or three years between the occurrence of a celestial omen and its presumed fulfillment is quite typical of Chinese astrology.

Systematic observation of lunar eclipses in China began around 400 CE, and from this period onward the official astronomers often timed the various phases of both solar and lunar eclipses with the aid of clepsydras (water clocks). Chinese astronomical techniques spread to Korea and Japan, and, especially after 1000 CE, eclipses were regularly observed independently in all three countries. However, the Chinese records are usually the most detailed.

The following account from the Yuanshi ("History of the Yuan Dynasty") of the total lunar eclipse of May 19, 1277 CE, follows the customary practice of quoting timings in double hours (12 to a combined day and night) and marks (each equal to Vioo of a day and night, or 0.24 hours):

14th year of the Zhiyuan reign period, 4th month, day guiyou [the 10th cyclical day], full Moon. The Moon was eclipsed. Beginning of loss at 6 marks in the hour of zi;

the eclipse was total at 3 marks in the hour of chou; maximum at 5 marks in the hour of chou; reappearance of light at 7 marks in the hour of chou; restoration to fullness at 4 marks in the hour of yin.

The three consecutive double hours zi, chou, and yin correspond, respectively, to 11 pm to 1 am, 1 am to 3 am, and 3 am to 5 am. The measured times are equivalent to 12:34 am (start of eclipse), 1:50 am (beginning of totality), 2:19 am (mid-eclipse), 2:48 am (end of totality), and 4:05 am (end of eclipse).

From the 3rd century CE onward, there is evidence of attempts at predicting eclipses by Chinese astronomers. Crude at first, these predictions reached their peak accuracy near the end of the 13th century, with typical timing errors of about one-fourth of an hour.

Assyrian

The Assyrian Chronicle, a cuneiform tablet that preserves the names of the annual magistrates who gave their names to the years (similar to the later Athenian archons or Roman consuls), records under the year that corresponds to 763-762 BCE: "Revolt in the citadel; in [the month] Siwan [equivalent to May-June], the Sun had an eclipse." The reference must be to the eclipse of June 15, 763 BCE, the only large eclipse visible in Assyria over a period of many years. A possible allusion to the same eclipse is found in the Hebrew

Bible: " 'And on that day,' says the Lord God, 'I will make the Sun go down at noon, and darken the earth in broad daylight' " (Amos 8:9). Amos was prophesying during the reign of King Jeroboam II (786-746 BCE) of Israel, and the eclipse would be very large throughout Israel.

Many references to both solar and lunar eclipses in the first half of the 7th century BCE are found among the divination reports to Assyrian kings. These tablets, which are now largely in the British Museum, were found in the royal archives at Nineveh. A text probably dating from 675 BCE carries the following account, indicating that the eclipse was regarded as an unfavourable omen:

The eclipse of the Moon which took place in Marchesvan [month VIII] began [in the east]. That is bad for Subartu. What [is wrong]? After it, Jupiter ent[ered] the Moon three times. What is being done to make its evil pass?

Babylonian by the Greek astronomer Hipparchus (2nd century BCE). Dates have been converted to the Egyptian 365-day calendar, while times have been expressed in hours instead of the original units.

The discovery and decipherment of vast numbers of cuneiform astronomical texts at the site of Babylon in the 1870s and '80s completely revolutionized the study of Babylonian astronomy. Most of the extant texts, dating from about 747 BCE to 75 CE, are in the British Museum. Numerous day-to-day astronomical diaries contain records of celestial phenomena, including many eclipses. Although most of the tablets are very fragmentary, additional Babylonian collections of eclipse reports—abstracted from the original diaries—also survive. An example of a lunar eclipse record, dating from 80 BCE, is as follows. Time intervals, presumably measured with the aid of a water clock, are expressed in US (time-degrees, equal to four minutes), while eclipse magnitudes are expressed in "fingers," each equal to M2 of the lunar diameter:

Until the discovery of the late Babylonian astronomical texts in the latter half of the 19th century, the Alexandrian astronomer Ptolemy's Almagest (2nd century CE) was the only source of Babylonian eclipse observations. Ptolemy cites several records of lunar eclipses, the earliest in 721 BCE. Unfortunately, the dates and observational details are not in original form but have been edited, presumably

Year 168 [Arsacid dynasty], that is year 232 [Seleucid kingdom]... month I, day 13... lunar eclipse... In 20 deg of night it made six fingers. Duration of maximal phase 7 deg of night, until it began to become bright. In 13 deg . . . 4 fingers lacking to brightness it set . . . [Began] at 40 deg before sunrise.

The date, when converted to the Julian calendar (April 11, 80 BCE), is exactly correct. Sunrise on this occasion would occur at 5:37 am, so that the measured start of the eclipse was at 2:57 am, and maximum phase (when half of the Moon was estimated to be in shadow) was at 4:31 am. When the Moon set, one-third of its disk was observed to be still in shadow. Use of "fingers" to express the magnitude of an eclipse (both lunar and solar) spread to Greece and hence to the Arab world. This convention was still fairly standard among astronomers worldwide until the 20th century.

Babylonian eclipse predictions, which were based on past series of observations, were fairly accurate for this early period. Timing errors averaged about two hours, and predictions gave a useful indication of the likelihood of an eclipse to intending observers.

Jewish

In his Antiquities of the Jews, the Jewish historian Flavius Josephus says the Judean king Herod died in the spring shortly after a lunar eclipse. Calculation shows that the only springtime lunar eclipses visible in Israel between 17 BCE and 3 CE took place on March 23, 5 BCE, and March 13, 4 BCE. The former was total in the mid-evening, while on the latter occasion about one-third of the Moon was in shadow around 3 am. These two dates are conveniently close to one another, although the latter date is usually preferred by chronologists—implying that Herod died in the spring of 4 BCE.

Greek

In a fragment of a lost poem by the 7th-century-BCE Greek poet Archilochus occur the words:

Nothing can be surprising any more or impossible or miraculous, now that Zeus, father of the Olympians, has made night out of noonday, hiding the bright sunlight, and fear has come upon mankind. After this, men can believe anything, expect anything.

This seems a clear reference to a total solar eclipse. The phenomenon has been identified as most likely the eclipse of April 6, 648 BCE, which was total in the Aegean and occurred during Archilochus's lifetime.

Fragments survive of other early Greek poetic descriptions of eclipses, and the ninth paean of Pindar, addressed to the Thebans, takes an eclipse of the Sun as its theme:

Beam of the Sun! O thou that seest from afar, what wilt thou be devising? O mother of mine eyes! O star supreme, reft from us in the daytime! Why hast thou perplexed the power of man and the way of wisdom, by rushing forth on a darksome track?

The 5th-century-BCE poet then proceeds to speculate on the meaning of this omen. Although he prays, "Change this worldwide portent into some painless blessing for Thebes," he adds, "I in no wise lament whate'er I shall suffer with the rest." This strongly suggests that Pindar, who was a Theban, had himself recently witnessed a great eclipse at his hometown. The most probable date for the eclipse is April 30, 463 BCE; modern calculations indicate that the eclipse was nearly total at Thebes.

The historian Thucydides records three eclipses during the Peloponnesian War, which began in 431 BCE and lasted for 27 years. The first of these was a solar obscuration that occurred in the summer of the first year of the war (calculated date Aug. 3, 431 BCE). On this occasion, the Sun assumed the form of a crescent in the afternoon before returning to its natural shape, and during the eclipse some stars became visible. This description agrees well with modern computations, except that no "star" apart from the planet Venus should have been seen. Seven years afterward, Thucydides noted that a "small" solar eclipse took place in the summer of the eighth year of the war (calculated date March 21, 424 BCE). Finally, a lunar eclipse occurred in the summer of the 19th year of the war (calculated date Aug. 27, 413 BCE). This last date had been selected by the Athenian commanders Nicias and Demosthenes for the departure of their armies from Syracuse. All preparations were ready, but the signal had not been given when the Moon was totally eclipsed in the evening. The Athenian soldiers and sailors clamoured against departure, and Nicias, in obedience to the soothsayers, resolved to remain thrice nine days. This delay enabled the Syracusans to capture or destroy the whole of the Athenian fleet and army.

Aug. 15, 310 BCE, is the date of a total eclipse of the Sun that was seen at sea by the tyrant Agathocles and his men after they had escaped from Syracuse and were on their way to Africa. Diodorus Siculus, a historian of the 1st century BCE, reported that "on the next day [after the escape] there occurred such an eclipse of the Sun that utter darkness set in and the stars were seen everywhere." Historians of astronomy have often debated whether Agathocles' ships sailed around the north or south coast of Sicily during the course of the journey. Modern computations of the eclipse track are still unable to resolve this issue, although they indicate that the eclipse was total over much of Sicily.

In the dialogue of the Greek author Plutarch (46-c. 119 CE) concerning the features of the Moon's disk, one of the characters, named Lucius, deduces from the phases of the Moon and the phenomenon of eclipses a similarity between Earth and the Moon. Lucius illustrates his argument by means of a recent eclipse of the Sun, which, "beginning just after noonday, made many stars shine out from many parts of the sky and tempered the air in the manner of twilight." This eclipse has been identified with one that occurred on March 20, 71 CE, which was total in

Greece. Whether Plutarch is describing a real, and therefore datable, event or is merely basing his description on accounts written by earlier authors has been disputed. However, his description is so vivid and original that it seems likely that Plutarch witnessed the eclipse himself. Later in the same dialogue, Lucius refers to a brightness that appears around the Moon's rim in total eclipses of the Sun. This is one of the earliest known allusions to the solar corona. Plutarch was unusually interested in eclipses, and his Parallel Lives, an account of the deeds and characters of illustrious Greeks and Romans, contains many references to both lunar and solar eclipses of considerable historical importance. There also are frequent records of eclipses in other ancient Greek literature.

Ptolemy in his Almagest records several lunar eclipses between 201 BCE and 136 CE. Most of these were observed at Alexandria in Egypt. For instance, the eclipse of May 1, 174 BCE, is described in the following words:

From the beginning of the eighth hour till the end of the tenth in Alexandria there was an eclipse of the Moon which reached a maximum obscuration of 7 digits from the north; so mid-eclipse occurred 2% seasonal hours after midnight, which corresponds to 2% equinoctial hours.

The local times of beginning and end correspond to about 12:55 am and 3:35

am, so mid-eclipse would have been close to 2:15 am.

Roman

Roman history is less replete with references to eclipses than that of Greece, but there are several interesting allusions to these events in Roman writings. Some, like the total solar eclipse said by Dio Cassius, a Roman historian of the 3rd century CE, to have occurred at the time of the funeral of Agrippina the Younger, the mother of the Roman emperor Nero, never took place. An eclipse of the Sun recorded by the historian Livy (64/59 BCE-17 CE) in a year corresponding to 190 BCE is of interest to students of astronomy and of the Roman calendar alike. Although Livy notes that the event happened in early July, the calculated date is March 14. Consequently, the Roman calendar in that year must have been more than three months out of adjustment.

What may well be an indirect allusion to a total eclipse of the Sun is recorded by Livy for a time corresponding to 188-187 BCE (the consulship of Valerius Messala and Livius Salinator during the Roman Republic):

Before the new magistrates departed for their provinces, a three-day period of prayer was proclaimed in the name of the College of Decemvirs at all the street-corner shrines because in the daytime, between about the third and fourth hours, darkness had covered everything.

The darkness took place some time after the election of the consuls (Ides of March), and, allowing for the confusion of the Roman calendar at this time, the total eclipse of July 17, 188 BCE, would be the most satisfactory explanation for the unusual morning darkness. Since the Sun is not mentioned in the text, the phenomenon possibly occurred on a cloudy day.

The total eclipse of the Moon on the evening of June 21, 168 BCE, has attracted much attention. This event occurred shortly before the defeat of Perseus, the last king of Macedonia, by the Romans at the Battle of Pydna. The contemporary Greek historian Polybius, in remarking on this eclipse, stated that "the report gained popular credence that it portended the eclipse of a king. This, while it lent fresh courage to the Romans, discouraged the Macedonians." Polybius added the wry comment: "So true is the saying, 'there are many empty things in war.'"

Medieval European

Following the close of the classical age in Europe, eclipses were in general only rarely recorded by European writers for several centuries. Not until after about 800 CE did eclipses and other celestial phenomena begin to be frequently reported again, especially in monastic chronicles. Hydatius, bishop of Chaves (in Portugal), was one of the few known chroniclers of the early Middle Ages. He seems to have had an unusual interest in eclipses, and he recounted the occurrence of five such events (involving both the Sun and the Moon) between 447 and 464 CE. In each case, only brief details are given, and Hydatius gives the years of occurrence in terms of the Olympiads (i.e., reckoning time from the first Olympic Games, in 776 BCE). During the total lunar eclipse of March 2, 462 CE (this date is known to be accurate), the Moon is said to have been "turned into blood." Statements of this kind are common throughout the Middle Ages, presumably inspired by the Hebrew Bible allusion in Joel (2:31). Similar descriptions, however, are occasionally found in non-Christian sources, as, for example, a Chinese one of 498 CE.

Given below is a selection from the vast number o f extant medieval European reports of eclipses. In many cases, the date is accurately recorded, but there also are frequent instances of chronological error.

In the year 733 CE, the continuation of Bede's Historia ecclesiastica gentis Anglorum ("Ecclesiastical History of the English People") contains an early reference to an annular eclipse on a date corresponding to August 14. When the eclipse was at its height, "almost the whole of the Sun's disk seemed to be like a black and horrid shield." Bede was the first historian to use "AD" dates systematically.

An occultation of a bright star by the eclipsed Moon in 756 CE (actually the previous year) is the subject of an entry in the chronicle of Simeon of Durham. Although Simeon lived some four centuries after the event, he is clearly quoting an eyewitness source:

Moreover, the Moon was covered with a blood-red color on the 8th day before the Kalends of December [i.e., November 24] when 15 days old, that is, the Full Moon; and then the darkness gradually decreased and it returned to its original brightness. And remarkably indeed, a bright star following the Moon itself passed through it, and after the return to brightness it preceded the Moon by the same distance as it had followed the Moon before it was obscured.

The text gives no hint of the identity of the star. Modern computations show that the Moon was totally eclipsed on the evening of Nov. 23, 755 CE. During the closing stages of the eclipse, Jupiter would have been occulted by the Moon, as seen from England. This is an example of the care with which an observer who was not an astronomer could describe a compound astronomical event without having any real understanding of what was happening.

Several eclipses are recorded in Byzantine history, beginning in the 6th century CE. By far the most vivid account relates to the solar eclipse of Dec. 22, 968

CE. This was penned by the contemporary chronicler Leo the Deacon:

At the winter solstice there was an eclipse of the Sun such as has never happened before ... It occurred on the 22nd day of the month of December, at the 4th hour of the day, the air being calm. Darkness fell upon the Earth and all the brighter stars revealed themselves. Everyone could see the disk of the Sun without brightness, deprived of light, and a certain dull and feeble glow, like a narrow headband, shining round the extreme parts of the edge of the disk. However, the Sun gradually going past the Moon (for this appeared covering it directly) sent out its original rays, and light filled the Earth again.

This is the earliest account of the solar corona that can be definitely linked to a datable eclipse. Although the appearance of the corona during totality is rather impressive, early descriptions of it are extremely rare. Possibly many ancient and medieval eyewitnesses of total eclipses were so terrified by the onset of sudden darkness that they failed to notice that the darkened Sun was surrounded by a diffuse envelope of light.

In a chronicle of the Norman rule in Sicily and southern Italy during the 11th century, Goffredo Malaterra records an eclipse of the Sun that, even though it caused alarm to some people, was evidently regarded by others as no more than a practical inconvenience:

[1084 CE] On the sixth day of the month of February between the sixth and ninth hours the Sun was obscured for the space of three hours; it was so great that any people who were working indoors could only continue if in the meantime they lit lamps. Indeed some people went from house to house to get lanterns or torches. Many were terrified.

This eclipse actually occurred on Feb. 16, 1086 CE. It was the only large eclipse visible in southern Italy for several years around this time; hence, the chronicler had mistaken both the year and day.

The German astronomer Regiomon-tanus (Johannes Müller) carefully timed nine eclipses between 1457 and 1471 CE. He compared his measured times with those calculated by using the Alfonsine Tables, a set of astronomical tables compiled two centuries beforehand that allowed computation of eclipses and planetary positions. His account of the lunar eclipse of Dec. 17, 1461 CE, is as follows:

The Moon rose eclipsed by 10 digits of its diameter [calculated]. Indeed I merely noted 8 [digits]. Moreover, from the Alfonsine computations the end of the eclipse occurred at 1 hour and 56

minutes after sunset. At this same end of the eclipse the altitude of the star Alhioth [Capella, or Alpha Aurigae] in the east was 38 degrees 30 minutes, whereas [the altitude of] the star Aldebaran [Alpha Tauri] was 29 degrees in the east. This was in the city of Rome.

In quoting star altitudes, Regiomon-tanus was following a practice favoured by medieval Arab astronomers. The local times corresponding to the two altitude measurements are respectively 5:21 PM and 5:25 PM; these compare with the Alfonsine result of 6:30 pM. Hence, the tables were more than an hour in error at this date.

Medieval Islamic

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, 1061 CE, was recorded by the Baghdad annalist Ibn al-JawzI, who wrote approximately a century after the event:

On Wednesday, when two nights remained to the completion of the month Jumada al-Ula [in 453 CE], 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, 1061 CE, 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 1176 CE are recorded in contemporary Arab history. Ibn al-Athlr, who was aged 16 at the time, described the event as follows:

In this year [571 CE] 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 Ramadan at Jazirat Ibn 'Umar, 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, 1176 CE. Calculation shows that the whole of the Sun would have been obscured over a wide region around Jazirat Ibn 'Umar (now Cizre, Turkey). Farther south, totality was also witnessed by the Muslim leader Saladin and his army while crossing the Orontes River near Hiamah (in present-day Syria). The chronicler 'Imad al-Din, 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, 'Imad al-Din dates the event one year too early (570 CE); the only large eclipse visible in this region for several years was that of 1176 CE.

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 1433 CE, but this occurrence caused some surprise to the contemporary Cairo chronicler al-Maqrizi:

On Wednesday the28th of Shawwal [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 Dhu 'l-Qa'da [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 CE, was recorded by the Cairo astronomer Ibn Yunus:

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, 1004 CE, at Ghazna (now Ghaznl, Afghanistan) and Jurjaniyyah (now Kunya-Urgench, Turkm.), the Persian scholar al-Blrunl 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

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