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“But we think it proper to hear from you what your thoughts are, for truly as regards this sect it is known to us that everywhere it is spoken against.”—Acts 28:22


Astronomical Calculations and the Count of Time

The Watchtower, March 15, 1969, pp. 184-7.
Copyright © 1969
Watchtower Bible and Tract Society of New York, Inc.

HISTORIANS generally have a preference for their own calculated chronologies over the chronology of the Bible. In this attitude they claim support from ancient astronomical calculations—some of them on tablets uncovered by the archaeologist’s spade. One historian even declares that "astronomical confirmation can convert a relative chronology, one that merely establishes the sequence of events, into an absolute chronology, a system of dates related to our [modern] calendar."1

How accurate is this claim? Of course, the celestial bodies were provided by the Creator to serve as a timekeeper for men upon earth. At Genesis 1:14 we can read: "Let luminaries come to be in the expanse of the heavens to make a division between the day and the night; and they must serve as signs and for seasons and for days and years." However, the efforts of men to relate ancient astronomical data to human events of the past involves a number of factors that allow for error—error in calculation and in interpretation.

At first glance it might seem to be quite simple to determine the date of some specific happening when an ancient cuneiform tablet informs us that the event coincided with some eclipse of the sun or moon. There are, however, partial eclipses and total eclipses, and it is quite important to know which it is in any given connection. Why? Well, according to The Encyclopœdia Britannica, any "particular town or city would on the average experience some 40 lunar eclipses and 20 partial solar eclipses in 50 years, [although] only one total solar eclipse in 400 years."2 So, the fixing of some specific historical date by means of an eclipse would be open to considerable question unless it was a case of a definitely stated total solar eclipse visible in a specific area. Unfortunately, such precise and vital information is rare in ancient sources.


Even as to the area of visibility for any given eclipse there is an element of uncertainty. Earth scientists have long understood that tidal currents in the oceans, coming into contact with sea bottom in shallower areas, may tend slightly to retard the earth’s rotation. "A number of scientists," reports a recent scientific work, "have found plausible evidence for the cumulative effect of tidal slowing in ancient records of eclipses. An eclipse is visible over only a small part of the earth’s surface. Moreover, the area of visibility can be calculated for eclipses that occurred centuries (or even millennia) in the past. It turns out, however, that modern calculations do not agree with the ancient records. The eclipses seem to have been observed in areas some hundreds of miles to the east of where they should have appeared."3

Here is an example that will reveal the weakness in this method of arriving at precise dates. There is one solar eclipse that is specially relied on by historians in their attempt to relate the chronology of Assyria with that of the Bible. This eclipse is mentioned in an Assyrian eponym (prominent name) listftn1 as taking place in the third month, counting from spring, of the ninth year of King Assur-dan III. Modern historians conclude that it was the eclipse occurring on June 15, 763 B.C.E.4 Counting back 90 years (or names, since they calculate a name for each year) on the eponym list, they arrive at 853 B.C.E. as the date for the battle of Qarqar in Shalmaneser’s sixth year. They claim that in other records Shalmaneser lists King Ahab of Israel as in the enemy coalition facing Assyria in that battle, and that twelve years later (Shalmaneser’s 18th year) he refers to King Jehu of Israel as one of those paying tribute to him.5 They then deduce that the year 853 B.C.E. marked the date of Ahab’s last year and 841 B.C.E. the start of Jehu’s reign.6

How sound are those calculations? Since the eponym list did not state the nature of this eclipse, whether partial or total, historians may not be warranted in concluding that it marked the year 763 B.C.E. Indeed, some scholars have preferred to settle for the year 809 B.C.E., during which an eclipse occurred that would have been at least partially visible in Assyria. But on the same basis there were also partial eclipses in the years 817, 857, and so on—each visible in Assyria.7 Nevertheless, historians object to any change from the solar eclipse of 763 B.C.E. on the ground that it would ‘introduce confusion into Assyrian history.’ Assyrian history, however, is already in considerable confusion.ftn2

The presence of King Ahab at the battle of Qarqar in the year 853 B.C.E. is quite unlikely. The Bible says nothing of it, and the translation of the Assyrian text on which this idea is based is quite conjectural. Bible chronology places Ahab’s death around 919 B.C.E. and the commencement of Jehu’s reign about 904 B.C.E. Shalmaneser’s mention of Jehu is not necessarily a reference to his first year. It could have been a later year of Jehu’s reign. Then, too, we have to keep in mind that the chroniclers of Assyria were given to juggling the years of their campaigns and even crediting their kings with receiving tribute from persons long dead. So there are weak links in the chain of data, including the astronomical data, relied on to synchronize Assyrian chronology and Bible chronology.


Lunar eclipses, as found in Ptolemy’s canon and presumably drawn from data in the cuneiform records, have been used in efforts to substantiate the dates usually given for particular years of the Neo-Babylonian kings. But even though Ptolemy may have been able to calculate accurately the dates of certain eclipses in the past, this does not prove that his transmission of historical data is correct. His relating of eclipses to the reigns of certain kings may not always be based on the facts. Additionally, the frequency of lunar eclipses certainly does not add great strength to this type of confirmation.

For example, a lunar eclipse in 621 B.C.E. (April 22) is used as proof of the correctness of the Ptolemaic date for Nabopolassar’s fifth year. However, another eclipse could be cited twenty years earlier in 641 B.C.E. (June 1) to correspond with the date that Bible chronology would indicate for Nabopolassar’s fifth year. Besides, this latter eclipse was total, whereas the one in 621 B.C.E. was partial.8

Perhaps the date of Herod’s death furnishes the best illustration of the uncertainty involved in dating by means of lunar eclipses. The Jewish historian Josephus shows Herod’s death to have occurred shortly after a lunar eclipse and not long before the start of the Passover season. Many fix 4 B.C.E. as the date of Herod’s death, citing as proof the lunar eclipse on the night of March 12/13 in that year. Due to this reckoning, some modern chronologers place Jesus’ birth in 5 B.C.E.

However, W. E. Filmer, writing in The Journal of Theological Studies, October 1966, shows the weakness of this reckoning. He points out that eclipses also took place on both January 9 and December 29 of the year 1 B.C.E. and that either of these could fit the requirements of an eclipse not long before Passover. Also he shows that the eclipse of January 9, 1 B.C.E., which was total, would better fit the circumstances than the one in 4 B.C.E., a partial eclipse. Summing up the matter, he says: "Thus, so far as the evidence of lunar eclipse goes, Herod may have died in either of the years 4 or 1 B.C.E., or even in A.D. 1." And either of these latter two dates would harmonize with the date of Jesus’ birth as calculated according to the Bible’s count of time, namely, the autumn of 2 B.C.E.

Thus it is obvious that eclipses of the moon of themselves are by no means sure pointers to the accuracy of dates in a relative system of chronology.


Not all the texts historians use to date events and periods of ancient history are based on eclipses, however. Astronomical "diaries" have been found. These diaries give the position (in relation to certain stars and constellations) of the moon at its first and its last visibility on a specific day in Babylon, along with positions of certain planets at these same times. For example, one such entry states that "the moon was one cubit in front of the rear foot of the lion." Modern chronologers point out that such a combination of astronomical positions would not be duplicated in thousands of years. These diaries also contain references to the reigns of certain kings and seem to coincide with Ptolemy’s canon.

Strong and incontrovertible though such evidence may appear to be, there are factors that greatly impair its strength. First, the observations made in Babylon may have contained errors. Babylon’s astronomers were more concerned about celestial phenomena occurring close to the horizon, at the rising or the setting of the sun or the moon. However, as viewed from Babylon, the horizon is often obscured by sandstorms, as Professor Neugebauer points out. He mentions that Ptolemy himself complained about "the lack of reliable planetary observations [from ancient Babylon]. He [Ptolemy] remarks that the old observations were made with little competence, because they were concerned with appearances and disappearances and with stationary points, phenomena which by their very nature are difficult to observe."—The Exact Sciences in Antiquity, page 98.

Another factor reducing the strength of testimony from extant astronomical diaries is the date of their writing. The majority of those now known were, in fact, written, not in the time of the Neo-Babylonian or Persian empires, but in the Seleucid period, about 364-312 B.C.E. True, they contain data relating to much earlier periods, and it is assumed that they were copies of earlier documents. However, the accuracy of such copying and the possibility of additions or adjustments certainly reduces the value of this evidence. Actually there is a serious lack of contemporary astronomical texts by which historians might establish the full chronology of the Neo-Babylonian and Persian periods.

Then, too, as in the case of Ptolemy, even if the astronomical data in the available texts, as now interpreted and understood, is accurate, this does not prove that the historical data accompanying the astronomical information is accurate. Just as Ptolemy used the reigns of certain kings (as he understood them) simply as a framework in which to place his astronomical data, so too the writers or copyists of the Seleucid period may have simply inserted in their astronomical texts what was "popular" chronology in their time. That "popular" chronology may well have contained errors.

To illustrate, an ancient astronomer of the second century B.C.E. might state that a certain celestial event took place in the year that, according to our calendar, would be 465 B.C.E. And his statement may prove to be correct when accurate computations are made to verify it. But he may also state that the year in which the celestial event took place was the ‘twenty-first year of Xerxes’ and be entirely wrong. Simply stated, accuracy in astronomy does not prove accuracy in history.


On the other hand, the dependability of the Bible’s time references is vouchsafed to us by the very characteristics of the Bible itself: its candor and honesty; the fact that everywhere we are made conscious of time as we peruse the various Bible books; the measurement of time by days, by seven-day weeks, by months and by years—a system of counting that is to be noted from the very outset of the Bible’s writing; the prophesied periods of time, so many of which we know to have been fulfilled exactly on time. All of this unites to assure us that the guiding power behind the numerous Bible writers was the One of whom it may be truly said that he is "the One telling from the beginning the finale, and from long ago the things that have not been done."—Isa. 46:10.

Did not the Bible long in advance foretell the seventy years during which Judea would lie desolate and her inhabitants would languish in Babylonian exile? In due time, the decree of Cyrus the Persian conqueror offered the faithful worshipers of Jehovah release and reinstatement in their own land. They were back in Jerusalem exactly on time.—Jer. 25:11, 12; Dan. 9:2.

The reader who will take the time to read the Bible passages at 1 Kings 6:1 and at Luke 3:1, 2 cannot but be impressed by the meticulous manner of referring to important historical dates. Sufficient data is offered so that the student may pin down the exact time of the event. The Bible writers themselves credit the factualness of their information to the Divine Author who merely used them as writing instruments. Surely, then, we can look to this same Source for accurate chronological data—data that is much more dependable than the speculations and conjectures of human historians!



1. The Old Testament World, Martin Noth, p. 272. (back)

2. The Encyclopœdia Britannica, 1965 ed., Vol. 7, p. 297. (back)

3. Time (1966), published by Time-Life Books; Science Library, p. 105. (back)

4. The Encyclopædia Britannica, 1959 ed., Vol. 7, p. 913. (back)

5. Ancient Near Eastern Texts, Pritchard, pp. 277-280. (back)

6. The Mysterious Numbers of the Hebrew Kings, E. R. Thiele, p. 53. (back)

7. Oppolzer’s Canon of Eclipses, Charts 17, 19, 21 (1962 ed.). (back)

8. Ibid., pp. 333, 334. (back)



1. The Watchtower, December 15, 1968, p. 758, "Assyria's Historical Records and the Bible." (back)

2. For evidence of this, see The Watchtower, December 15, 1968, pp. 757, 758, "Assyria's Historical Records and the Bible." (back)

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