ANCIENT ECLIPSES It is not surprising that, in ancient times when eclipses were regarded as portents, a large number of eclipses should have been mentioned in history or in literature, in addition to those which are recorded in astronomical treatises or on astronomical tablets.
The value of these records may be classified as follows : Literary and historical, depending on the interest which they aroused, the notice taken of them, and their connection with events. (2) Chronological, in so far as they enable us, by com puting their dates, to verify chronological systems resting on other evidence and to supply dates for events connected with the eclipses. (3) Astronomical, including the determination by an cient astronomers of the periods and motions of the sun and moon, and by modern astronomers of the mean rate of change of those motions, which, in astronomical terminology, is called secular acceleration.
The Shih King, or Book of Poetry, contains a lamentation caused by an eclipse of the moon, followed by an eclipse of the sun. The dates are clearly defined and are found to agree with the lunar eclipse of Aug. 21 and the solar eclipse of Sept. 6 in B.C.
The eclipses recorded in the Spring and Autumn Annals possess a chronological and astronomical rather than a literary interest.
(2) Assyrian.—The Assyrian eponym canon, which preserves the names of the annual magistrates who gave their names to the years, records under the year which corresponds to our 763-762 B.C.:-"Insurrection in the city of Assur. In the month Sivan the sun was eclipsed." The reference must be to the eclipse of the sun on June 15 in 763 B.C. A reference to the same eclipse has been found in Amos viii. 9, "And it shall come to pass in that day, saith the Lord God, that I will cause the sun to go down at noon, and I will darken the earth in the clear day." (3) Greek.—In the Odyssey Homer twice makes the unrecog nized Odysseus predict that Odysseus will return "as the old moon wanes, and the new appears," that is, at new moon, when alone an eclipse of the sun is possible. In one of these passages he predicts vengeance on his wife's suitors. On the day when Odysseus was to become known and slay the suitors, the seer Theoclymenus notes among other portents of gloom that "the sun has perished out of heaven, and an evil mist has spread over all." This was interpreted by Plutarch and Eustathius as a total eclipse of the sun. Some modern scholars have regarded it as merely a vision of the seer. Schoch (the Observatory, xlix. [ 1926] pp. 19-21) has suggested an identification with the solar eclipse of April 16 in 1178 B.C., which was total in or near Ithaca. But it is not improbable that the story of the eclipse belongs to legend rather than to history.
In a fragment of a lost poem by Archilochus occur the words : "Nothing there is beyond hope, nothing that can be sworn im possible, nothing wonderful, since Zeus, father of the Olympians, made night from mid-day, hiding the light of the shining sun, and sore fear came upon men." According to Aristotle the words come from a passage, abusing a lady, probably Archilochus's former fiancée Neobule, who is supposed to have belonged to Paros. The life of Archilochus was divided between Paros and Thasos. The phenomenon described has been identified as the total eclipse of the sun on April 6 in 648 B.C.
Small fragments survive of other poetic descriptions of eclipses, and the ninth paean of Pindar, addressed to the Thebans, takes an eclipse of the sun as its theme. Sandys translates the opening lines as follows : "Beam of the sun ! 0 thou that seest afar, what wilt thou be devising? 0 mother of mine eyes! 0 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?" Pindar then proceeds to speculate on the meaning of the eclipse as a portent. The poem probably refers to the solar eclipse of 463 B.C., April 30, which was nearly total at Thebes.
The most famous of ancient eclipses was a total eclipse of the sun which happened according to Herodotus during a battle between the Lydians and Medes. The portent induced them to cease from fighting and conclude peace. Herodotus further in forms us that Thales of Miletus predicted this eclipse to the Ionians for the very year in which it happened. Babylonians were certainly predicting eclipses about this time by means of the 18 years' cycle known as the Saros. But, as that cycle gives eclipses for every year, the statement about Thales must, if true, mean that he predicted that an eclipse of the particular year would attain a great magnitude. Such a prediction can be made by the 18 years' cycle without any mathematical computation. The eclipse was certainly that of 585 B.C., May 28, and must have been predicted by means of the eclipse of 603 B.C., May 18. Several ancient writers have preserved 585 B.C. or some neigh bouring year as the date of the eclipse.
Thucydides comments on the frequency of eclipses during the Peloponnesian war. The most interesting of these were the solar eclipse of 431 B.c., Aug. 3, when, we are told, "the sun assumed the shape of a crescent and became full again, and during the eclipse some stars became visible," a statement that agrees well with modern computation, and the lunar eclipse of 413 B.C., Aug. 27. That date had been selected by the Athenian commanders, Nicias and Demosthenes, for the departure of their armament from Syracuse. All preparations were ready, but the signal had not been given, when the moon was eclipsed. The 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.
The year 31 o B.C., Aug. 15, is the date of a total eclipse of the sun, which, as we are informed by Diodorus and Justin, was seen by Agathocles and his men the day after he had sailed from Syra cuse on his way to Africa. Modern computations of the eclipse track render it probable that he sailed to the north of Sicily.
In Plutarch's Dialogue on the Face which appears in the Orb of the Moon, one of the characters, called Lucius, deduces from the phases of the moon and the phenomena of eclipses a similarity between the earth and the moon and illustrates his argument by means of a recent eclipse of the sun, "which, beginning just after noon, showed us plainly many stars in all parts of the heavens, and produced a chill in the temperature like that of twilight." A little further on Lucius refers to a certain brightness which appears round the moon's rim in total eclipses of the sun. Nicolaus Struyck identified this eclipse with that of A.D. 71, March 20, and the identification has been confirmed by Ginzel after a very exhaustive discussion. There are numerous other references to eclipses in Greek literature.
(4) Roman.—There is a very large number of eclipses recorded in Roman history. One which has attracted the attention of students alike of astronomy and of the Roman calendar is stated by Cicero to have occurred in the 3 50th year from the foundation of Rome and to have been described by the poet Ennius as fol lows :—"On the Nones of June the sun was covered by the moon and night." This would appear to have been the solar eclipse of 400 B.e., June 21, which reached a total or almost total phase at Rome a few minutes after sunset. It seems to show that in that year the calendar month of June began 16 days later than in the calendar as reformed by Julius Caesar.
The eclipse of the moon in 168 B.C., June 21, has attracted much attention. The Romans were at that time at war with Macedon, and Polybius informs us that the eclipse of the moon was interpreted as an omen of the eclipse of a king and thus en couraged the Romans and discouraged the Macedonians. Cicero states that Sulpicius Gallus explained the eclipse on the following day, while Livy states that the eclipse was predicted by Gallus and took place on the night before the battle of Pydna, which, according to him, was fought on Sept. 4 of the Roman calendar of that time. It seems clear that the story has grown with repe tition and that there is no evidence that the eclipse was predicted or that it was on the night before the battle of Pydna.
Use of Eclipses for Chronological Purposes.—Although no continuous era has been used since ancient times, dates are fre quently expressed in terms of regnal years, or are named after consuls or other officials of whom lists have been preserved. In these cases it is important to be able to equate certain specific years thus defined with years before the Christian era. This can be done whenever the date of an eclipse or other identifiable and calculable astronomical phenomenon is given in an ancient record.
The received Chinese chronology can be confirmed accurately by eclipses from 719 B.C. onwards. The chronology of Ptolemy's canon of kings, which gives the Babylonian series from 747 to 539 B.C., the Persian series from S38 to 324 B.C., the Alexandrian series from 323 to 3o B.C., and the Roman series from 3o B.C. on wards, is confirmed throughout by eclipses. The eclipse of 763 B.C., recorded in the eponym canon, enables us to carry the chronology back with certainty through the period covered by that canon, to 893 B.C. Assyrian, Babylonian and Persian chro nology provide a stable chronology for the countries with which Assyria, Babylon and Persia came into contact, but there is no check from eclipses on Greek or Egyptian historical chronology before the Persian period. Identifiable eclipses recorded under named Roman consuls extend back to B.C. The dated eclipses of Ennius and Pydna and one in 190 B.C. can be used to determine the position of Roman calendar months in the natural year, and occasionally eclipses help us to fix the precise dates of a series of events, such as those connected with the Athenian disaster at Syracuse.
These cycles govern the recurrence of eclipses. It has been seen that Thales probably used such a cycle. In a Babylonian observa tion tablet of 568 B.C. mention is made of failure to observe a predicted eclipse of the moon. The eclipse is found by computa tion to have been real, but invisible at Babylon. It was doubtless predicted by cycle. Tables based on the saros go back to the 4th century B.C. Eclipses of the moon give more accurately than any other kind of observation the actual time when sun and moon are in opposition. From an early date the Babylonian astronomers must have deduced from them not only the mean interval be tween two conjunctions, but the principal inequality in the mo tion of the moon and the similar inequality in the motion of the earth, or, as on their geocentric theory they conceived it, of the sun, and they were able to define the periods of these inequalities, which astronomers call the anomalistic month and year.
In the same way, since eclipses happen only when the two luminaries are stationed at intersections of their orbits called nodes, and since the path of the shadow in a lunar eclipse depends on the position of the centre of the sun in relation to the node, they were also able to determine the position and motion of the nodes. By assuming, what is approximately true, that the saros of 6,5851 days contained an exact number (a) of synodic months, or revolutions of the moon measured from the sun, (b) of anomalistic months, or revolutions of the moon measured from her apogee or perigee, that is, from her furthest removal from and closest approach to the earth, and (c) of draconic months or revolutions of the moon measured from her node, the early astronomers, perhaps in the 6th century B.C., computed the rela tive motions of the sun and moon, the lunar perigee and apogee, and the nodes. About 500 B.C. Naburiannu, apparently from a more accurate study of eclipse observations, obtained improved values which for the motion of the moon from the sun were 1o" per annum too small, for the moon from her perigee 20" per annum too great, and for the moon from her node 5" too small. Still more accurate values were obtained by Kidinnu about 383 B.C., from whom they passed to the Greek astronomer Hipparchus. In the system of Naburiannu the distance of the moon from her node was used for the prediction of the magnitude of lunar eclipses.
(2) In Modern Astronomy.—Ancient eclipses are of the high est value for the determination of "secular accelerations," that is, for the determination of the progressive, as distinct from the periodic, changes in celestial motions. Edmund Halley asserted in 1695 his belief that the moon's motion was subject to accelera tion, but did not specify the amount of the acceleration. In Richard Dunthorne demonstrated from a comparison of the recorded with the computed times of eclipses distributed over 2,000 years that such an acceleration existed and assigned to it the value of 1o" a century. By this is meant that the effect of the acceleration is to produce an advance of '0" in the moon's longi tude in the course of a century. Laplace in 1786 discovered that such an acceleration should be the gravitational effect of the secular diminution in the eccentricity of the earth's orbit. But J. C. Adams showed in 1853 that the acceleration due to this cause amounts to 6" only in a century. The residue must be ex plained by other causes.
The most recent values are 11" a century acceleration of the moon, of which 5" is unexplained, and about 1.5" a century for an acceleration of the earth's motion suggested by P. H. Cowell in 1905. It is.usual to regard the latter as an apparent effect of a retardation of the earth's rotation, which is our standard of time. This should produce an apparent acceleration of the Moon times as great as that of the earth. But, since the unexplained acceleration of the moon is only about 3.3 times as great as that of the earth, it becomes necessary to suppose that there is a real secular retardation of about 15" a century in the moon's motion. It is commonly supposed that tidal friction is the main cause of both retardations. (See MOON.) BIBLIOGRAPHY.-J. K. Fotheringham, Historical Eclipses (1921), and Bibliography.-J. K. Fotheringham, Historical Eclipses (1921), and "A Solution of Ancient Eclipses of the Sun," Monthly Notices of the Royal Astronomical Society, lxxxi. (1920), 104-126. Fr. Boll, s.v. Finsternisse, Pauly-Wissowa, Realencyklopddie, vi. (19o9), 2329-64, with a list of recorded eclipses. P. Schnabel, Berossos (1923), and Kidenas, Hipparch and die Entdeckung der Prdzession, Zeitschrift fur Assyriologie, N.F. iii. (1926), 1-6o, for Babylonian astronomy without special reference to eclipses. (J. K. F.)