In the history of chronology, few dates are as significant as 747 BC. It marks the beginning of what is known as the Nabonassar Era.
Astronomer Claudius Ptolemy, writing in the 2nd century AD, claimed he possessed Babylonian records of astronomical observations stretching back to the time of Nabonassar. The centuries old data enabled Ptolemy to refine his calculation of celestial orbits.
In a modern calendar, the first day of the Nabonassar Era - Thoth 1, Nabonassar 1 - corresponds to February 26, 747 BC.
Present day historians echo Ptolemyís claim. They profess to have uncovered old cuneiform tablets with observations dating back to exactly 747 BC.
Apparently some of the Babylonian records available to Ptolemy made their way into the archives of present-day museums. Historians and astronomers collaborated to date the records and fine-tune chronology. The resulting time-line is considered astronomically sound from the present to the 8th century BC.
Astronomical records from China, Egypt, Central America, the Indian subcontinent and elsewhere have survived and received scholarly attention. As matters now stand, only the eclipses logged in the Spring and Summer Annals (Ch'un-ch'iu) from China significantly augment the extensive documentation from the Ancient Near East.
The Ch'un-ch'iu, the Almagest and Babylonian cuneiform tablets all record observations dated to the 8th century BC. The synchronism has stimulated much scholarly speculation.
Some historians seek a noteworthy historical or astronomical event that sets this century apart. Others argue there is nothing special about the epoch. They doubt the reliability of ancient observations and maintain chronology prior to Hellenistic times cannot be astronomically confirmed. Undeterred, optimistic chronologists routinely extrapolate beyond the 8th century, using astronomy to fix dates in the 2nd and 3rd millennium BC.
Is astronomical chronology confirmed as far back as 747 BC? That is, have historians assembled the record of astronomical events in a valid continuous timeline from 747 BC to the present?
If the timeline extends to the 8th century BC and no further, then what prompted the change in the way societies keep track of time? A review of the chronological evidence may sort out divergent views.
The inquiry focuses on the period 750 to 400 BC in the Ancient Near East with side trips to other times and places. A series of research papers and related evidence is provided to help readers assess relevant issues.