1, Tropical year, and sidereal year are two different concepts.

2, The tropical year is the interval between two transits of mean Sun through mean Equinox.

3, The tropical year is a phenomenon of the precession of the equinoxes in astronomy.

4, During a tropical year the sun moves from Vernal Equinox to Vernal Equinox.

5, Applying tropical year and lunation,[http:///tropical year.html] the exchange formula of calendar and solar calendar could be derived.

6, A tropical year is a measurement of time from one winter solstice to the next.

7, Applying tropical year and lunation, the exchange formula of lunar calendar and solar calendar could be derived.

8, The Julian calendar approximated the mean tropical year as 365.25 days and proposed 366-day leap years for every one divisible by four.

9, Pope Gregory XIII mandated a reform to the calendar; his Gregorian calendar approximated the mean tropical year as 365.2425 days.

10, This paper advocates that the six states of the dragon described in the hexagram of Qian are six celestial phenomena of the star of the green dragon in a tropical year.