Julian year

In astronomy, a Julian year (symbol: a) is a unit to measure time. It has exactly 365​¹⁄₄ days of 86,400 seconds each.^[1][2][3][4] That is the average length of the year in the Julian calendar used in Western societies in previous centuries, and for which the unit is named. Nevertheless, because a Julian year measures duration rather than designates date, the Julian year does not correspond to years in the Julian calendar or any other calendar. Nor does it correspond to the many other ways of defining a year. It is also not connected to the Julian day used in astronomy.

References

1. P. Kenneth Seidelmann, ed., The explanatory supplement to the Astronomical Almanac, (Mill Valley, Cal.: University Science Books, 1992), pp. 8, 696, 698-9, 704, 716, 730.
2. "Measuring the Universe". International Astronomical Union. Retrieved March 22, 2012.
3. International Astronomical Union. "Recommendations Concerning Units". Archived from the original on February 16, 2007. Retrieved February 18, 2007. Reprinted from the "IAU Style Manual" by G.A. Wilkinson, Comm. 5, in IAU Transactions XXB (1987).
4. Harold Rabinowitz and Suzanne Vogel, The manual of scientific style (Burlington, MA: Academic Press, 2009) 369.