<P> The calendar followed in some parts of South India (mainly in Tamil Nadu) is solar . It has a leap year every four years . </P> <P> The Baha'i calendar is a solar calendar composed of 19 months of 19 days each (361 days). Years begin at Naw - Rúz, on the vernal equinox, on or about March 21 . A period of "Intercalary Days", called Ayyam - i - Ha, are inserted before the 19th month . This period normally has 4 days, but an extra day is added when needed to ensure that the following year starts on the vernal equinox . This is calculated and known years in advance . </P> <P> The Iranian calendar is an observational calendar that starts on the spring equinox and adds a single intercalated day to the last month (Esfand) once every four or five years; the first leap year occurs as the fifth year of the typical 33 - year cycle and the remaining leap years occur every four years through the remainder of the 33 - year cycle . The system used is more accurate and more complicated, and is based on the time of the March equinox as observed from Tehran . The 33 - year period is not completely regular; every so often the 33 - year cycle will be broken by a cycle of 29 years . </P> <P> In Ireland and Britain, it is a tradition that women may propose marriage only in leap years . While it has been claimed that the tradition was initiated by Saint Patrick or Brigid of Kildare in 5th century Ireland, this is dubious, as the tradition has not been attested before the 19th century . Supposedly, a 1288 law by Queen Margaret of Scotland (then age five and living in Norway), required that fines be levied if a marriage proposal was refused by the man; compensation was deemed to be a pair of leather gloves, a single rose, £ 1 and a kiss . In some places the tradition was tightened to restricting female proposals to the modern leap day, February 29, or to the medieval (bissextile) leap day, February 24 . </P>

How many leap years from 1990 to 2017