RE: Iranian Calendar
Hello, I am slow these days to answer, sorry for that; I'm getting over the exams now. I read the mailings for the last few days about the calendar. It's nice to see new and knowledgeable friends like Hooman Mehr and Ordak D. Coward taking part here. There were things new for me and mixed up a bit. Let me brief out what I understand out of the mess about the solar calendar. Please correct me wherever I'm wrong. The calendar Hejrie Shamsi comes in types: - The early solar calendar (Hejrie Shamsie Borji), an observational solar calendar with tropical years. The months are synchronized observationally with the duration sun stays in each of the 12 zodiacal constellations, which vary between 29 to 32 days for each month with an accumulation of 365 or sometimes 366 days a year. - The old Jalali calendar, a true solar calendar with twelve 30-day months followed by 5 or 6 additional days at the end to fill a complete solar year. It starts with 'Norooze Jalali' [*]. - The modern Jalali calendar in use in Iran (Iranian calendar), reworked on the old Jalali calendar and uses the same leap structure; consists of six 31-day plus six 30-day months followed by a month of 29 days or 30 during a leap year. It starts with 'Norooze Jalali'. - The afghan Jalali calendar. It has the same month lengths as the Iranian calendar but the leap years are synchronized with the concurrent Gregorian years. Afghans celebrate Norooze Jalali but the first day of the year might start with an offset of 1 day from the Iranian calendar. [*] Norooze Jalali: The first day of a Jalali year. It is defined by the 'Tahvil' moment, the exact tick that the center of sun passes the point of vernal equinox in the northern hemisphere of the earth. If Tahvil happens before noon of the meridian of Tehran, then Norooz is the same day otherwise Norooz is the next day. There are different methods to estimate the precise moment of VE. The effort is to find the one that is as much as possible close to the real occurrence of the phenomenon. Omid ___ PersianComputing mailing list [EMAIL PROTECTED] http://lists.sharif.edu/mailman/listinfo/persiancomputing
RE: Iranian Calendar
On Mon, 17 May 2004, Hooman Mehr wrote: Hi Omid and Connie, MSDN way of specifying Hijri calendar is like saying the length of any month in Gregorian calendar is 30 days plus or minus two days -- true but not very useful. [...] Hi Hooman, The Hijri calendar introduced in MSDN does not give you a totally accurate date, since as you know there are many many elements and dependancies around finding a correct Hijri date. It also does not work based on a specific region. It simply lets you adjust it manually by 2 days. It means it has always a probability of 1 or 2 days of error and seems that they prefer this descripency in return of the other advantages it gives: to cover every variant and every region, and the ability to fix the calendar in case that the observations change the authoritative estimated version of the calendar at any time. It is possible to implement the Hijri calendar the way ODC suggested, using online tables of Hijri adjustments for the past years but it still limits the divices to be online and yet it's impossible again to find assured correct dates in the future. With the current conditions in mind I think it is not out of sence to choose this particular calendar for the OS to be ordinarily useable rather than tailoring it for complex calendarical conversions. Omid ___ PersianComputing mailing list [EMAIL PROTECTED] http://lists.sharif.edu/mailman/listinfo/persiancomputing
RE: LeapYears of Iranian Calendar
On Fri, 21 May 2004, Ordak D. Coward wrote: I guess the best thing to do: - is get an archive of the last 50 years of official times of vernal equinox, or saal tahveel, and compute the length of year for each year. Fit them with linear or quadratic curves. Look at Birashk's method and see how much Birashk's length of year differs from official length of year. Also, look at the real variation of length of years, compute the calendar for the next 1000 years using both Birashk and the curves. Decide if using the curves will result in less error. Good idea, if we can collect the list of Tahveel moments for the passed years, I think I can easily prepare the curves with my implemented calendar. It uses .NET DateTime objects with a presicion of 100 nanosecond (namely a tick). It also supports dates up to year 9378 A.P (Anno Persico). But before that I have to manipulate a line of code to work with Birashk's leap years. Here is an attempt to guesstimate when the official calendar starts to diverge from Birashk's. A rough look at the last few years variation of length of years show a variation of up to 5 minutes. So, each 144 years or so (24hours / 10 minutes) , we have a year whose VE is +/- 5 minutes of noon. Hence, as long as we use a constant for the length of year, it is very likely to see discrepancies once every 144 years. However, this WILL happen as early as 1404. That is, if my calculations are correct Birashk's method gives year 1404 as a leap year, but I get 1403 as a leap year. (I am using some acceptable length of years). That is, the VE of year 1404 should happen around 12:30pm which if it considered afternoon, it shall be Esfand 30th of 1403. THIS IS IMPORTANT AND SHOULD BE DEALT WITH. No amount of observational errors can compensate this. Considering the computational power available today, it is a shame if we stick to a method using constant length of year which were only appropriate for pre-computer era. I guess you're right. Since Showraaye Taghvim announces their own calculation of the VE every year, their estimation may disagree with that of Birashk in the next few decades. So we should choose the algorithm that matches the real world as close as possible. -- ODC Omid ___ PersianComputing mailing list [EMAIL PROTECTED] http://lists.sharif.edu/mailman/listinfo/persiancomputing
