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
Solar Hijri calendar calendar of 365 days for three consecutive years plus an extra day in the next year, save for exceptions to the latter in three out of every four centenaries). The start of the year and its number of days remain fixed to one of the two equinoxes, the astronomically important days which have the same duration of the sun. It results in less variability of all celestial bodies comparing a specific calendar date from one year to others. Each of the twelve months corresponds with a zodiac sign. The first six months have 31 days, the next five have 30