Mysterious relation between PI, Gregorian and Islamic calendars
is the period taken by the Earth to complete an orbit around the Sun and, again,
there are a number of ways in which this can be measured. But for calculating a
calendar that is to remain in step with the seasons, it is most convenient to
use the tropical year, since this refers directly to the Sun's apparent
annual motion. The tropical year is defined as the interval between successive
passages of the Sun through the vernal equinox (i.e., when it crosses the
celestial equator late in March) and amounts to 365.242199 mean solar days.
The Muslim Era is computed from the starting point of the year of the emigration (Hegira); that is, from the year in which Muhammad, the prophet of Islam, emigrated from Mecca to Medina, AD 622. The second caliph, 'Umar I, who reigned 634-644, set the first day of the month Muharram as the beginning of the year; that is, July 16, 622.
The years of the Muslim calendar are lunar and always consist of 12 (lunar) months, each month beginning approximately at the time of the New Moon.The months are alternately 30 and 29 days long except for the 12th, Dhu al-Hijjah, the length of which is varied in a 30-year cycle intended to keep the calendar in step with the true phases of the Moon. In 11 years of this cycle, Dhu al-Hijjah has 30 days, and in the other 19 years it has 29. Thus the year has either 354 or 355 days. No months are intercalated, so that the named months do not remain in the same seasons but retrogress through the entire solar, or seasonal, year (of about 365.25 days) every 32.5 solar years.
Now the following equation shows the intime relation between the islamic year, the Gregorian year and the transcendent magical number Pi =3,1415.... It's to say that also history and dates are mathematically linked to each other. The conversion is usually made by special software. Try the below equation to see the accuracy of the results and controll the precision with a Hegira/Gregorian converter.
622 AD is the year of Hegira. If you are in the second half of the year use 622.
Use 622,5 if you are in the first half.
Pi = 3,14159265.....
( Gregorian - 622 ) x ( Pi/100 + 1) = Hegira Year
Ref. : http://fakir60.tripod.com/