玛雅历法，为什么算得那么准？

The Maya lived long ago in America. 玛雅人很久以前生活在美洲。 They watched the stars for hundreds of years. 他们观测星星，观测了几百年。 They made a calendar with their own hands. 他们亲手做出了一套历法。 Their year numbers were almost perfect. 他们算出来的年份准得惊人。 The error was smaller than one day. 误差还不到一天。 That is amazing for people long ago. 这对古人来说太了不起了。