He also distinguishes between tropical year and sidereal year , the first time the introduction of calendar precession , measured precession for 45 years , a time difference in november .
他还区分了回归年和恒星年,首次把岁差引进历法,测得岁差为45年11月差一度。
With this definition , a sidereal year is something like 365.256363 solar days .
有了这样的定义,那么一个太阳年就是365.256363个太阳日。
So , if you started a clock when the sun was at the first position , it would take longer than a sidereal day for the sun to get back into the same position in order to compensate for the orbital motion of the earth .