اطلاعات مربوط به کشور ايران Iran Information
Iran Information / Iranian calendar
Persians have always been keen on the idea and importance of calendar system for
as long as their documented history has been recorded. They are among the first
cultures to use solar calendar systems and have always favoured the solar
calendar. In general, the sun has always, even to this day, had a special
meaning and great symbolic significance in the Iranian culture.
Today Iran uses a solar calendar with a leap day system which is older but more
scientifically accurate than the Greqorian calendar. The present Iranian
calendar's leap day system was devised in the 11th century by a panel of
scientists including Omar Khayyam, who was one of the foremost leading
mathematicians and astronomers of his time, but today is well-known in the West
for his poetry.
The Iranian solar calendar year begins with the midnight closest to the instant
of vernal equinox, when the sun enters the northern hemisphere. The first day of
this calendar year is also the day of the greatest festival of the year in Iran
called Norouz (a single word made up of two parts, no and rouz, meaning "new
day"). The calendar consists of 12 months which have Persian names. The first
six months are 31 days each, the next five 30 days, and the last month has 29
days but 30 days in leap years. The reason the first 6 months have 31 days and
the rest 30, is not a random decision -- it has to do with the fact that the sun
moves slightly more slowly along ecliptic in the northern spring and summer than
in the northern autumn and winter.
The Persian new year is determined by noon-time observation of the Northern
spring equinox. If between two consecutive noons the sun's altitude rises
through its equinoctial altitude then the first noon is on the last day of one
calendar year and the second noon is on the first day (Norouz)of the next
Typically leap years are devised and used by various solar calendar systems,
usually every four years. Four-year leap years add 0.25 day to each year in the
period. But that is a slight overcompensation compared to the actual behaviour
of the sun. Remedying this overcompensation, after about every seven four-year
leap years, the Persian solar calendar produces a five-year leap year, thus
following a thirty-three year cycle for many centuries before interruptions by
single twenty-nine year subcycles.
This general picture of the Persian calendar's leap-year behaviour contrasts
with other ill-informed predictive algorithms which are based on confusion
between the astronomers average tropical year (365.2422 days, approximated with
mistaken near 128-year cycles) and the mean interval between vernal equinoxes
(365.2424 days, approximated here with a near 33-year cycle).
Iran General View