Century leap year thus the leap day February 29 in those years always falls on a Tuesday (dominical letter BA). The Gregorian calendar yields an average year that currently tracks the annual revolution period of the Earth more closely than the older Julian calendar, in which every fourth year (including end-of-century years) is a leap year. The Julian formula adds too many leap days (3 every 400 years), causing the Julian calendar to drift gradually with respect to the astronomical seasons. Over time, natural events such as the spring equinox began to occur earlier and earlier in the Julian calendar. The Gregorian calendar
Chinese calendar solstices, is divided into 24 solar terms. Different versions of the traditional calendar might have different average solar-year lengths. One solar year of the 1st century BC Tàichū calendar is (365.25016) days. A solar year of the 13th-century Shòushí calendar is (365.2425) days, identical to the Gregorian calendar. The additional .00766 day from the Tàichū calendar leads to a one-day shift every 130.5 years. Pairs of solar terms are climate terms, or solar months. The first solar term is "pre-climate" (), and the second is "mid-climate" (). There are generally 11 or 12 complete months, plus two incomplete months around