Page "Astronomical year numbering" Paragraph 2

The system is so named due to its use in astronomy.

Few other disciplines outside history deal with the time before year 1, exceptions being dendrochronology, archaeology and geology, the latter two of which use ' years before the present '.

Although the absolute numerical values of astronomical and historical years only differ by one before year 1, this difference is critical when calculating astronomical events like eclipses or planetary conjunctions to determine when historical events which mention them occurred.