Astronomical year numbering

Astronomical year numbering is a method of numbering years before the start of the anno Domini era. In astronomical year numbering, the year 1 BC is numbered 0, the year 2 BC is numbered -1, and in general the year n BC is numbered –(n–1). Years AD are unchanged. The system is so named due to its original use by astronomers. It is more convenient to have a year 0 when subtracting years and computing time intervals than span the epoch. However, astronomers mostly find it convenient to use Julian days when making computations.