From: ghbr@fmg.bt.co.uk (Hossein Bagherzadeh Rafsanjani)
Newsgroups: soc.culture.iranian
Subject: The Iranian calender
Date: 12 Jan 93 11:01:17 GMT
Organization: British Telecom

In article <1993Jan11.202048.28128@netcom.com> bavafa@netcom.com (Hooshyar Naraghi) writes:

> In article <1820@rwja.umdnj.edu> majidi@rwja.umdnj.edu (Masoud Majidi) writes:
> >mehdizadeh@asl.slb.com writes:
> >
> >>I was wondering if any one out their knows what the Persian Calender is
> >>based upon?  In other words what happened 1372 years ago?
> >
> >.  .  . Also 'shams' means sun and it refers to how we measure the length
> >of the year (i.e. the length of our year is the time it takes the earth to 
> >orbit the sun, ~355.4 days)
		    ^^^^^
> Could you by any chance mean lunar year ('hejri ghamari') instead?  If my
> 'akAber' class notes don't fail me, 'shamsi' year was 365 days and few
> fraction (~6 hours).

That is correct.  And as we go through the time lapse between the
beginning of the western and Iranian calendars, we may face more
related questions - such as the relation between the two calendars.
So, for the benefit of those who were not around (SCI) last year, I
repost an article on the subject.  (May be the subject should also be
covered in the FAQ file.)


(The article is written in LaTeX.  If you don't have this facility, simply
remove all words with a "\" in front of them, and may be some of the "{}"
symbols and/or the texts inside them.)

-hossein
-----------------------------------cut here--------------------------------
\documentstyle{article}
\author{Dr. Hossein Bagherzadeh Rafsanjani} 
\title{\Huge The Great Leap Years Gap}
\date{April 1992}
\begin{document}

\maketitle 

\vspace{.35in}
{\Large We have all been used to see the Iranian and Western leap years
coincide.  However, this year is going to be the last we experience this!
Read on ...}

\vspace{.2in}

The new western ({\em Gregorian}\footnote{Named after Pope Gregory XIII who
introduced the latest changes in the calendar in 1582.}) leap year of 1992 has
already begun and the Iranian ({\em Jalaali}\footnote{Named after {\it
Jalaal-ol-Din Malek-shaah-e Saljuqi} by {\em Omar Khayyam} who re-worked it in
late fifth century {\em hejri}.}) leap year of 1370 has just ended.  This meant
that the month of February had 29 days, and Esfand (the last month of the the
Iranian calendar) 30 days, with a small variation in correspondence between the
two calendars for the 20 days in between.  And on the 21st of March, the
Iranian new year's day, the relation between the two calendars reverted to
normal with no discrepancies in the dates.

There is of course nothing new in that.  We are all used to both the Jalaali
and Gregorian calendars.  These are both solar and have the same length of 365
days in normal years and 366 days in leap years.  The leap years come usually
once every four years.  And for all we can remember, the leap years in the two
calendars have come so close to each other that the distance between the two
extra (leap) days in the two calendars have been less than three weeks (from
the end of February to the end of Esfand = 20th March).

This close correspondence between the two calendars has reduced the problem of
converting one calendar to the other to the very minimum.  Indeed, apart from
the last 20 days of the Jalaali leap years, one could usually use any calendar
of any year to find the corresponding dates between the two systems.  And for
those particular dates in the leap years, the Gregorian calendar is just one
day behind the Jalaali one, when compared to other years.  (For instance, 8th
of March, the International Women's Day, corresponds to 18th of Esfand in the
leap years and to the 17th of Esfand in other years.)

However, this cozy relationship between the two calendars is going to end for
the time being, i.e., at least for 99 years (unless the calendar system
changes)!  Why?  Because while there will be a three--year gap to the next
Gregorian leap year of 1996, we need to wait an extra year to the next Jalaali
leap year.  The next Jalaali leap year is not going to be in 1374 (as may have
been expected) but 1375.  And the next time the two leap years correspond to
each other as they do now, will be in the Gregorian year of 2096 and Jalaali
year of 1474.

The reason is both complicated and fascinating.  But before going into that,
let us have a look at the Jalaali calendar and appreciate some of its unique
features.

The Jalaali calendar is more ``natural'' than the Gregorian calendar.  It
starts with the natural cycle of the year, the first day of spring (for the
northern hemisphere).  As such, it has no national, regional or religious
significance.\footnote{The years' count is based on a historical religious
event ({\em hejrat}).  But that's a different story.  Gregorian calendar is
based on religion for both its base date and start of the year.} It is truly
universal.  Every season is associated with three full months of the year.  So
no confusion arises as which day of the year, e.g., the beginning of a season
is.  The first six months all have 31 days and the second six months all have
30 days in leap years, with the last month having 29 days in non-leap years.

Compare these with the Gregorian calendar.  There you will find no easy
correspondence between months and seasons' starts and endings, nor between the
natural and calendar years.  The months have arbitrary length of seven 31 days,
four 30 days and one 28/29 days interleaved irregularly.  It took only a Roman
dictator like Augustus to increase the days of the month of August by one day
just because July, the previous month (named after his predecessor Julius
Caesar), had 31 days in it.  Luckily, for Iranians, in spite of being ruled by
stream of dictators who occasionally fancied playing with calendars (the last
one done by the Shah who tried to add some 1180 years to the base date!), the
Jalaali calendar has remained almost intact.

Add to the above features, the fact that the Jalaali year follows closely the
movement of the earth (round the sun).  A natural solar year is neither 365
days nor 366.  It is something like 365 days, 5 hours and 49 minutes.  While
for westerners, the new year begins at midnight, for us there is an exact time
(to the seconds) worked out by astronomy which specifies the beginning of the
new year.  This is known as ``{\em tahvil-e saal}''\footnote{A solar
calendar year begins at the point when the sun appears to cross the equator
from the southern hemisphere to the northern hemisphere as viewed from the
center of the earth.}.  However, for the calendar purposes, a day (of 24 hours)
can either belong to the past year (say, the last day of Esfand) or the new
year (1st of Farvardin).  So what we do is this: if the exact moment of {\em
tahvil-e saal} is before midday (Tehran time), we regard the same day as the
New Year's Day (1st Farvardin).  Otherwise, the New Year begins in the
following day.  This has made the Jalaali calendar year much more accurate than
the Gregorian one (details later).

Now, because the natural year is approximately 365 days and 6 hours, it means
that {\em approximately} every four years we have an extra day in the year -
hence the leap years.  But the year's length is about 11 minutes shorter than
that.  So, over the years, these 11 minutes added together affect the cycle of
the leap years.  For instance, while this year {\em tahvil-e saal} occurs just
after midday (Tehran time), and so the following day will be {\em Nowruz}, in
four years time it will happen before midday, and so the same day will be
regarded as {\em Nowruz} and not the following day.  As a result, the leap year
is pushed to the next year.  This happens every 33 years, when the differences
of 11 minutes add up to approximately 360 minutes - equal to 6 hours.  That is
enough to cause an extra non-leap year every 33 years.

And that is how the Jalaali calendar system is organized: In this calendar 8
years out of 33 are leap years.  The leap years are those with a remainder
(after dividing by 33) of 1, 5, 9, 13, 17, 22, 26, and 30.  For instance, 1370,
the current year, divided by 33 leaves 17 as the remainder, and so is a leap
year.  Moreover, the above figures show that there will be a five-year span
(instead of the usual four years) between this leap year and the next.  The
last time the same thing happened was between the leap years of 1337 and 1342
(Gregorian years 1958-59 and 1963-64, respectively). 

And how does the Gregorian calendar deal with these anomalies?  Here too, they
have made things much simpler for themselves and not bothered about the natural
year.  They have fixed the leap years for every four years except for the years
which are divisible by 100 but not by 400!  So, the year 2000 will be a leap
year (as it is divisible by 400) but not, say, 2100.  In this way, they have
managed to compensate for the shortfall of 11 minutes per year over a span of
400 years.  A clever way but not consistent with the actual size of a natural
year.  Moreover, the system is not accurate over a longer period of time, but
who cares?

The only problem is for us who have to deal with the two systems, and convert
the days from one to another.  The effect of these variations in the leap years
is that, when converting the dates, there may be one or two days difference
between the corresponding days from one year to another.

In view of this fact, it may be worthwhile to look back at the years before
1339.  If you happen to have a date in the years before 1339 (before March
1960, to be exact) converted into the Gregorian calendar, say your date of
birth in the passport, it is very likely that the conversion is {\em wrong}.
But it may also be the case even for the dates between the 10th to 30th of
Esfand in every leap years, anyway.  Passport issuing officers, past and
present, have no time for such niceties as these calculations require, and
usually use a current calendar for converting dates to each other.  The
question is: does it {\em really} matter, anyway?  Not for the bulk of Iranians
who never care(d) about their birthdays.  But over here, if you have taken an
insurance on your life, the insurance company may be interested to check your
{\em exact} date of birth if the insurance happens to mature on a date on the
borderline.  Enough to give some sleepless nights to many!  \footnote{For more
information, see any good encyclopedia or : L. P.  Elwell-Sutton, {\em
Elementary Iranian Grammar}, Cambridge University Press, 1977; ISBN 0-521-
09206-X.  There is also a calendar table on p. 219 of this book.}
\end{document}
Newsgroups: soc.culture.iranian,soc.culture.arabic