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The Nabonassar era - a counting system used in ancient Egypt, with particular importance in astronomy and chronology because of its use by the Alexandrian geographer Klaudius Ptolemy. The beginning of the era was 1 tot 748 BC. The Nabonassar era was counted from the beginning of the Babylonian king Nabonassar (748 BC), beginning with the New Year of the Egyptian calendar (1 day of the month tot). Since the Egyptian year was 365 days (there were no leap years), the New Year (1 tot) systematically retreated with respect to the seasons, the beginning of the Era fell on 26 February, and at the time when Claudius Ptolemy used it in 160 The year after Chr., it coincided with July 13 of the Julian calendar. Ptolemy used the Nabonassar era in his canon of kings, a compilation of the Babylonian, Assyrian, Persian, Macedonian and Roman rulers, important for chronology. He also used it during his observations. Nabonassar was used by astronomers throughout the Middle Ages. Copernicus also wanted to take advantage of Ptolemy's observations. Bibliography

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