元是中国古代历法的时间单位。指纪之岁数（回归年数）与12个岁星纪年之最短循环周期[1]。又称历法起算的理想基准点（历元）为上元[2]，上元至编历时的年数为上元积年。推算上元积年的制历方法始于《三统历》。历代为求精确而数值逾亿[3]，故统天历虚设上元积年，一直到《授时历》终废上元积年[4]。
文内注释
Wikiwand in your browser!
Seamless Wikipedia browsing. On steroids.
Every time you click a link to Wikipedia, Wiktionary or Wikiquote in your browser's search results, it will show the modern Wikiwand interface.
Wikiwand extension is a five stars, simple, with minimum permission required to keep your browsing private, safe and transparent.
