Astronomical dating is the dating of an historical event with reference to a known astronomical event occurring either coincident with, shortly before, or shortly after the historical event in question.
The movements of the sun, moon, planets, stars, and other objects in the sky are more predictable than are the movements of any other object. The random wind and water currents that affect the movement of objects on the earth are absent in outer space. Even the solar wind is not powerful enough to affect materially the movements of the largest observable objects.
If one can predict the movement of any object, then one can back-track that object. Better yet, one can determine within a very narrow tolerance where a given object was in the sky, and how long ago a spectacular coincidence event (such as an eclipse of the sun or moon) occurred.
If, then, a reliable historical record exists that mentions that event, then modern investigators can calculate when it occurred, with reference to whatever epoch one wishes to use, and with reference to modern historical records.
Types of records
Astronomical dating works by synchronizing one type of historical record with another. Any record that sets a date is a good candidate for such synchronization. The following types of records use dates of one sort or another:
- Direct astronomical records, that actually record astronomical events.
- Royal proclamations or other government records.
- Sales receipts, bills of lading, and other merchants' records.
- Birth, death, and other "vital" records.
- Census records.
Nor is this an exhaustive list.
Application to Biblical Chronology
Internal Dating: Scripture OnlyThe Bible contains multiple records of the above types: many government records, an abundance of vital records, and even some census records and something close to merchants' records (for example, records of the materials used in the set-up of the Tabernacle and later in the building of the Temple of Jerusalem). The Bible is, however, short on astronomical records. Two specific references would qualify. Here is one:
And here is another:
And it came to pass, as they fled from before Israel, and were in the going down to Bethhoron, that the LORD cast down great stones from heaven upon them unto Azekah, and they died: they were more which died with hailstones than they whom the children of Israel slew with the sword. Then spake Joshua to the LORD in the day when the LORD delivered up the Amorites before the children of Israel, and he said in the sight of Israel, Sun, stand thou still upon Gibeon; and thou, Moon, in the valley of Ajalon. And the sun stood still, and the moon stayed, until the people had avenged themselves upon their enemies. Is not this written in the book of Jasher? So the sun stood still in the midst of heaven, and hasted not to go down about a whole day. Joshua 10:11-13 (KJV)
And Isaiah said, This sign shalt thou have of the LORD, that the LORD will do the thing that he hath spoken: shall the shadow go forward ten degrees, or go back ten degrees? And Hezekiah answered, It is a light thing for the shadow to go down ten degrees: nay, but let the shadow return backward ten degrees. And Isaiah the prophet cried unto the LORD: and he brought the shadow ten degrees backward, by which it had gone down in the dial of Ahaz. II_Kings 20:9-11 (KJV)
Neither event would be predictable, however, because each of these events likely affected the movements of all objects. One can only calculate one event with reference to another.However, Amos, according to James Ussher, successfully predicted total or near-total eclipses of the sun. For example:
Astronomical records available to Ussher himself clearly showed that three near-total eclipses of the sun occurred within a few years of Amos' prophecy, in 791 BC, 771 BC, and 770 BC--each one occurring during a major pilgrimage feast (the first during Pentecost, the second during Tabernacles, and the last during Passover). Amos himself dates his prophecies as referring to events during the reigns of Uzziah, King in the Southern Kingdom, and Jeroboam II, King in the Northern Kingdom:
Shall not the land tremble for this, and every one mourn that dwelleth therein? and it shall rise up wholly as a flood; and it shall be cast out and drowned, as by the flood of Egypt. 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: And I will turn your feasts into mourning, and all your songs into lamentation; and I will bring up sackcloth upon all loins, and baldness upon every head; and I will make it as the mourning of an only son, and the end thereof as a bitter day. Amos 8:8-10 (KJV)
The words of Amos, who was among the herdmen of Tekoa, which he saw concerning Israel in the days of Uzziah king of Judah, and in the days of Jeroboam the son of Joash king of Israel, two years before the earthquake. Amos 1:1 (KJV)
The earthquake probably took place in 787 BC, since Jeroboam II died three years later. Amos therefore uttered his prophecies two years earlier, in 789 BC. Though one eclipse had already taken place, two other eclipses remained to take place, both early in the reign of King Menahem of the Northern Kingdom--nineteen years after Amos had predicted them, at a time when astronomy was not yet well-enough developed to predict eclipses of the sun and moon.
(Interestingly, both Ussher and Edwin R. Thiele agree that Uzziah and Jeroboam II were each on their respective thrones during this period--except that Thiele implies that Amaziah was also on the throne of the Southern Kingdom at this time, and that Uzziah was his viceroy at the time--a viceroyship that began eight years before Uzziah was born. See Southern Kingdom for details.)
External Dating: Scripture and Secular Records
The most momentous example of using external, secular astronomical records to date a major Biblical event is the dating of the death of Herod the Great. Herod ordered the execution of all boy-children two years old or younger in Bethlehem, in an effort to destroy Jesus Christ. Shortly thereafter, Herod died. A major astronomical event occurring on the occasion of his death dates it positively at 4 BC--which means that the actual year of the Birth of Christ is earlier than that, probably 5 BC.
Applications to Secular History
Because astronomical events are so easy to back-track, the comparison of astronomical back-calculations to historical records remains today the best way to synchronize the ancient calendars with modern calendars. Indeed, events in secular records must match any eclipses of the sun or moon, planetary or stellar conjunctions, or (more rarely) cometary sightings that the ancient records mention, or else the date makes no sense. Ussher used astronomical records extensively in his dating of secular events. His dates agree remarkably well with those of later historians.
- James Ussher, The Annals of the World. See especially paragraphs 562-3 for Ussher's treatment of Amos' predictions of near-total solar eclipses.