


   (hdate/hcal Version 1.0)					    HDATE(1L)



   NAME
     hdate, hcal - Islamic (Hijri) date	and calendar

   SYNOPSIS
     hdate [day	month year]
     hdate [-h day month year]

     hcal [-h] [[month]	year ]

   DESCRIPTION
     For a given date, hdate prints the	corresponding Islamic (Hijri) date.
     If	no arguments are given,	it uses	the current (today's) date.  If	the
     -h	command	option is specified, hdate takes the given date	as a Hijri
     date, and translates it back to the common	calendar.  (The	common calen-
     dar is the	Gregorian calendar for years after 1582	and the	Julian calen-
     dar for years before that.)

     hcal prints a calendar with both common and Hijri dates. If no arguments
     are given,	the current month is used.  If a year is specified, the	pro-
     gram outputs a calendar for that entire year.  If a month is also speci-
     fied, a calendar just for that month is printed.	If the -h option is
     specified,	hcal takes the given month/year	as a Hijri month/year, and
     produces a	calendar accordingly.	If no Hijri month/year is given, a
     calendar for the current Hijri month is printed.  When the	-h option is
     used, the program will also print the time	of the start of	the new	moon
     whose first visibility marks the beginning	of the Hijri month.

     The month is a number between 1 and 12.  For Christian Era	(C.E.) dates,
     a year must be positive (i.e., A.D.).  For	Hijri dates, a positive	year
     signifies After Hijrah or Anno Hegirae (A.H.); a negative year signifies
     Before Hijrah (B.H.). (The	year after 1 B.H. was 1	A.H.; there is no
     year zero.)

     The Hijri year consists of	12 (purely) lunar months.  They	are: (1)
     MoHarram; (2) Safar; (3) Raby` al-awal; (4) Raby` al-THaany; (5) Jumaada
     al-awal; (6) Jumaada al-THaany; (7) Rajab;	(8) SHa`baan; (9) RamaDHaan;
     (10) SHawwal; (11)	Thw al-Qi`dah; and (12)	Thw al-Hijjah.	 The most
     important dates in	the Islamic year are: 1	MoHarram (new year); 1
     RamaDHaan (first day of fasting); 1 SHawwal (`iyd al-FiTr); 8-10 Thw
     al-Hijjah (the Hajj to Makkah); 10	Thw al-Hijjah (`iyd al-'aDHHae).

   EXAMPLES
     To	find out the current Hijri date, simply	enter:

	  hdate

     To	display	the Gregorian date corresponding to the	1st of RamaDHaan (the
     9th month)	of the Hijri year 1413,	type:

	  hdate	-h 1 9 1413

     To	find out the Hijri date	of the battle of HiTiyn, enter:



									    1






   HDATE(1L)					     (hdate/hcal Version 1.0)


	  hdate	4 6 1187

     To	produce	a (Gregorian/Hijri) calendar for December 1992,	enter:

	  hcal 12 1992

     To	display	a (Hijri/Gregorian) calendar for the year 1413 Hijriah,
     enter:

	  hcal -h 1413


   NOTES and METHOD DESCRIPTION
     For religious reasons, the	beginning of a Hijri month is marked not by
     the start of a new	moon, but by a physical	(i.e., an actual human)
     sighting of the crescent moon at a	given locale.  From the	Fiqhi stand-
     point, one	may begin the fast in RamaDHaan, for example, based on
     "local" sighting (IKHTILAF	AL-MATALE') or based on	sighting anywhere in
     the Muslim	World (ITTEHAD AL-MATALE').  Although different, both of
     these positions are valid Fiqhi positions.

     Astronomically, some data are definitive and conclusive (i.e. the time
     of	the BIRTH of the crescent).  However, determining the VISIBILITY of
     the crescent is not as definitive or conclusive; rather it	is dependent
     upon several factors, mostly optical in nature.

     Efforts for obtaining an astronomical criterion for predicting the	time
     of	first lunar visibility go back the the Babylonian era, with signifi-
     cant improvements and work	done later by Muslim and other scientists.
     These efforts have	resulted in the	development in a number	of criteria
     for predicting first possible sighting of a crescent.  However, there
     remains a measure of uncertainty associated with all criteria developed
     thus far. Moreover, there has been	little work in the area	of estimating
     crescent visibility on global (as opposed to local) scale.	 Until this
     happens, no Hijri calendar	software can be	100% reliable, and actual
     crescent sighting remains essential especially for	fixing important
     dates such	as the beginning of RamaDHaan and the two `iyds.

     The slight	differences in printed Islamic calendars, worldwide, can be
     traced to two factors: (1)	the absence of a global	criterion for first
     visibility; and (2) the use of different visibility criterion (or method
     of	calculation).  Weather conditions and differences in the observer's
     location also explain why there are sometimes differences in the obser-
     vances of Islamic dates, worldwide.

     hcal and hdate use	one of the simplest astronomical criterion for ear-
     list lunar	visibility.  The criterion is a	local one and is based on the
     moon's age	since the lunar	conjunction (the start of the new moon).

     The minimum recorded age of the crescent moon for first visibility	is
     around 13 1/2 hours.  hcal	and hdate take this into consideration to
     determine the likelihood of the crescent being sighted just after the
     first sun set (assumed to occur at	7:30p.m.) following the	new moon.
     And since there is	no agreed upon international Lunar date-line, hcal


   2






   (hdate/hcal Version 1.0)					    HDATE(1L)


     and hdate currently use Makkah (+3	GMT) for the locale.

     It	is the authors'	view that hdate/hcal produces dates/calendars that
     are more reliable than many of the	Islamic	calendars printed annually by
     various Muslim communities.  The programs,	moreover, provide astronomi-
     cally based information which can be used to support the actual sighting
     of	crescent moons.

   AUTHOR
     Waleed A. Muhanna (wmuhanna@magnus.acs.ohio-state.edu).














































									    3



