About the converter General Considerations How to use the converter Causes of the Error Future Modifications History of the Hijri (Islamic) Calendar History of the Christian Calendar

About the converter:

* It was written using JavaScript 1.2. Once launched, it can perform conversions even if disconnected from the internet.

* Version 8.5 uses mathematical equations to convert between different Calendrical systems, you may notice a change of result with each change of version, but the change would always be in the +/- 1 day range.  Always quote the version of the converter when converting dates!!

* In this version, conversion from & to the Chinese calendar is possible. A few bugs here & there were also corrected. The moon picture has more varieties now. A major change was made in the methods used to calculate the time & position of the new moon, which makes it more accurate to predict the start of lunar months.

* Converter v8.5 is a UNIVERSAL converter. It can convert between any of the following calendars: "Gregorian/Western/New Style", "Julian/Old Style", "Hijri/Islamic", "Chinese" & the "Hebrew/Jewish." It can also Convert any Julian day 'JD', which is the number of days since 12:00:00 UT 1/1/4713 BCE 'Julian' & any Modified Julian Day (MJD, = JD-2400000.5) to any of the above.

* This converter has +/- 1 day error when converting from the Hijri calendar to other systems & vice versa. The converter otherwise is virtually error free. Read about the causes of the error below.

* Major contributions to this version came from 2 fabulous books, "Astronomical Algorithms" & "Calendrical calculations the millennium edition."

General Considerations:

* Use of the Gregorian Calendar started in Rome in 1582 CE & was not adopted by other countries at once, some adopted it just in the 20th century, so make sure that the date you are referring to is in either the Gregorian, Julian, Gregorian Proleptic or the Julian Proleptic Calendar. Read about the history of the Julian & Gregorian Calendars below.

* Some countries used to start the year in March till recent centuries, so make sure that you correct the year if that was the case because my converter has the year starting on Jan 1st. Read an example of the confusion that happened due to these differences in the Gregorian Calendar history below.

* A.D. (Anno Domini, In the year of the Lord) is equivalent to C.E. (Current Era). B.C. (Before Christ) is equivalent to B.C.E. (Before Common Era).

* In my converter, I use out of convenience the abbreviations AD & BC for Christian Dates, AH (Anno Hejirae) & BH (Before Hijra) for the Hijri Calendar. On a similar note, there is AM/BC & AC/BC for the Hebrew & Chinese calendars respectively. Note that in my converter there is no year 0. Make sure to correct the years when comparing dates with converters using year 0.

* Because ANNO DOMINI means "in the year of the Lord," its abbreviation A.D. was originally placed before rather than after a date: The Roman conquest of Britain began in A.D. 43 (or began A.D. 43). In edited writing, it is still usually placed before the date. But, by analogy with the position of B.C. "before Christ," which always appears after a date (Caesar was assassinated in 44 B.C.), A.D. is also frequently found after the date in all types of writing, including historical works: The Roman emperor Claudius I lived from 10 B.C. to 54 A.D. Despite its literal meaning, A.D. is also used to designate centuries, being placed after the specified century: the second century A.D. - I wrote this section from "Webster's encyclopaedic unabridged dictionary of the English language" after a kind e-letter objecting my use of A.D. after years. In my converter, I use A.D. after the date out of convenience & will keep it that way. The same thing applies to the use of A.H.

* The Chinese year result is written in the day/month/year format & in the year/cycle format followed by the stem-branch format in its Chinese name & English equivalent.

* You can only put a Chinese calendar entry as a day/month/year format unfortunately!

How to use the converter:

* This converter is VERY user friendly. It is viewed best using a 800*600 resolution or higher (sorry !!). Drag the converter window if its borders are outside the boundaries of your screen.

* If the converter window seems to be crowded with its contents, try decreasing the Font Size.

* The converter is very user-friendly, you could put in the date with your mouse without even touching the keyboard,

* Now, choose the calendar from which you want to convert from. The converter by default starts as "From Gregorian to others." You have a selection to choose from.

* If you change the type of calendar that you're converting from, the names of the months on the month key pad will change to help you correlate between the name of the month & the month's order between other months. This will return to default when choosing to convert from the Gregorian or the Julian Calendars. Make sure that you tick the leap box if the Chinese month is a leap one & the number in the month box at that instance would be the number of month just preceding it.

* Is it AH or BH / AD or BC / AM or BC / AC or BC? Just toggle between them by pressing the button showing them, no "-" signs allowed, & there is no such thing in my converter as year 0. Year 0 is 1 BC or 1 BH, year -1 is 2 BC or 2 BH.

* Press FINISH. The results of the conversion will appear in the frame just on your upper right corner.

* when choosing the "Julian day to others" or "Modified Julian Day to others," you must TYPE IN (no mouse) an integer in the day box, & then press finish. The integer which you have typed in corresponds to 12:0:0 UT. The converter will automatically subtract .5 from your Julian day entry to make it equivalent to 0:0:0 UT, so make sure that you notice that.

* There is a wide range of years that the converter would accept. Going outside that range, or submitting a mismatched date would generate an error message.

* I will keep the older version (7.4) for a while, just in case you wanted to correct a previous conversion.

Causes of the Error:

1. The Same Gregorian date may have actually 2-4 Hijri equivalent dates according to the PLACE & TIME of the day. The 1st of Ramadan in Jordan for example could be the 30th of Shaban in some other parts of the world according to the sighting of the moon, also 1st of Ramada at an instance in San Francisco could be equivalent to the 2nd of Ramadan in China because of time zone difference. To add on top that, the Islamic & Hebrew days begin at sunset, so the 1st of August before sunset & after sunset will correspond to 2 different Islamic & Hebrew days.

2. The conversion from & to the Hijri calendar is a pure mathematical one, & for the reasons of conversion, I had to make the Islamic day start at midnight. This is not true, but it makes conversion easier & wouldn't affect the +/-1 day error that much.

In reality, the sighting of the moon is the basis of determining when the month starts. Islamic Astronomers have a fixed 30 year cycle which has the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th, and 29th years as leap years of 355 days, this however is not taken into consideration by many Islamic countries which consider the physical sighting of the moon as the only method of determining the beginning of a lunar month. You have to remember also that the Islamic day starts at sunset & ends on the next sunset !

But come now !!! Even with all of these errors, the total error is +/- 1 day, & even the most accurate of calculations will have the same error at the end (look at the paragraph above) !! That makes my converter reliable, especially if you knew that the method of determining the 1st day changes from one country to another, bringing any converter to making predictions, not more !

3. The Gregorian calendar was implemented in 1582 CE in ROME, so dates before May, 1582 CE are calculated in reference to the first day the Gregorian calendar was implemented "Gregorian Proleptic Calendar."

4. Many countries adopted the Gregorian Calendar years after that date. So you see, some of the errors are out of my hand & some can be corrected! (see below). The transition between calendars gave the people the sense of losing days, although when referring to the proper calendar, not a single day was missed, but the problem was that no one referred to the proper calendar.

5. One way to be 100% sure about the Hijri conversion is to know FOR SURE the day of the week on which a certain Hijri date occurred, then you can correct the Gregorian day result to that day of the week (That is if the results didn't match ??!!), & remember to correct to the nearest day or then you will FOR SURE be 7 days off your mark.

Future Modifications:

* I will hopefully try to minimize the memory space used by the program .

* I hope to add some information about the history of the Calendars, I'm currently searching for some proper resources, May be someone can give me some help !!!!

* My next additions to this converter (if the output window can take it) would be the Hindi & Persian calendars. the time frame however is still unknown.

History of the Hijri (Islamic) Calendar:

The Islamic Calendar, which is based purely on lunar cycles, was first introduced in 638 CE by the close companion of the Prophet Muhammad and the second Caliph, `Umar ibn Al-Khattab (586-644 CE). He did it in an attempt to rationalize the various, at times conflicting, dating systems used during his time. `Umar (Omar) consulted with his advisors on the starting date of the new Muslim chronology. It was finally agreed that the most appropriate reference point for the Islamic Calendar was the Hijra (Hijrah, Hegira). The actual starting date for the Calendar "Epoch" was chosen -on the basis of purely lunar years, counting backwards- to be the first day of the first month "1st of Muharram" of the year of the Hijra. The Islamic (Hijri) Calendar -with dates that fall within the Muslim Era- is usually abbreviated AH in Western languages from the Latinized Anno Hejirae "In the year of the Hijra." 1st of Muharram, AH 1 corresponds to Friday July 16th, 622 CE in the Julian Calendar.

The Hijra, which chronicles the flight of the Prophet Muhammad from Mecca (Makkah) to Medina (Madinah) in September 622 CE, is the central historical event of early Islam. It led to the foundation of the first Muslim city-state, a turning point in Islamic and world history.

Modified from "A Brief Introduction To The Islamic (Hijri) Calendar," by Waleed Muhanna

Important Dates:

The following dates that confirm the accuracy of the converter have been mentioned in "Mā shāa wa-lam yathbut fī al-sīrah al-Nabawīyah" by Muḥammad ibn Abd Allāh Ūshan quoting Abdulla Al-Saleem in his book "Taqweem Al-Azman" (Both books are in Arabic)

The reader is encouraged to read Thomas Djamuluddin's "Calendar Conversion Program Used to Analyze Early History of Islam" which mentions that Hijra took place in year 0 of the Hijri/Islamic calendar (1 BH in my converter which doesn't support the year 0). In his paper, the actual date of Hijra is Monday 5 / 10 / 621 Julian (Corresponding to 13 /3 /1 BH Hijri/Islamic in my converter). This is an opinion that I don't share simply because most scholars have mentioned that Prophet Muhammad spent 10 lunar years (not 11) in Medina (Madinah) from Hijra until he died in 11 AH Hijri/Islamic.

History of the Julian & Gregorian Calendars:

The original Roman calendar, introduced about the 7th century BCE, had 10 months with 304 days in a year that began with March. Two more months, January and February, were added later in the 7th century BCE, but because the months were only 29 or 30 days long, an extra month intercalated approximately every second year. The days of the month were designated by the method of counting backward from three dates: the calends, or first of the month; the ides, or middle of the month, falling on the 13th of some months and the 15th of others; and the nones, or 9th day before the ides.

The Roman calendar became hopelessly confused when officials to whom the addition of days and months was entrusted abused their authority to prolong their terms of office or to hasten or delay elections.

In 45 BCE Julius Caesar, upon the advice of the Greek astronomer Sosigenes (flourished 1st century BCE), decided to use a purely solar calendar. This calendar, known as the Julian calendar, fixed the normal year at 365 days, and the leap year, every fourth year, at 366 days. Leap year is so named because the extra day causes any date after February in a leap year to "leap" over one day in the week and to occur two days later in the week than it did in the previous year, rather than just one day later as in a normal year.

The Julian calendar also established the order of the months and the days of the week as they exist in present-day calendars. In 44 BCE Julius Caesar changed the name of the month Quintilis to Julius (July), after himself. The month Sextilis was renamed Augustus (August) in honour of the Roman emperor Caesar Augustus, who succeeded Julius Caesar. Some authorities maintain that Augustus established the length of the months we use today.

The Julian year was 11 min and 14 sec longer than the solar year. This discrepancy accumulated until by 1582 CE the vernal equinox occurred 10 days early and church holidays did not occur in the appropriate seasons. To make the vernal equinox occur on March 21, as it had in 325 CE, the year of the First Council of Nicaea, Pope Gregory XIII issued a decree dropping 10 days from the calendar. To prevent further displacement he instituted a calendar, known as the Gregorian calendar, that provided that century years divisible evenly by 400 should be leap years and that all other century years should be common years. Thus, 1600 was a leap year, but 1700 and 1800 were common years.

The Gregorian calendar, or New Style calendar, was slowly adopted throughout Europe. It is used today throughout most of the Western world and in parts of Asia. When the Gregorian calendar was adopted in Great Britain in 1752, another correction of an 11 day discrepancy was made; the day after September 2, 1752, became September 14. The British also adopted January 1 as the day when a new year begins. The Soviet Union adopted the Gregorian calendar in 1918, and Greece adopted it in 1923 for civil purposes, but many countries affiliated with the Greek church retain the Julian, or Old Style, calendar for the celebration of church feasts.

In the history of Western civilizations, the principal problems of chronology are encountered in the reconciliation of dates in the various calendars, such as the Julian, Gregorian, and Muslim. For example, an article appeared in the Edinburgh Courant of February 19, 1706. The article was an abridgment of one published in the London Gazette of February 13, 1705, which, in turn, was a translation from the Amsterdam Gazette of February 22, 1706. All three were published in the same week. The discrepancy in year was caused by the fact that Scotland and the Low Countries began the year on January 1, while England, until 1752, began it on March 25. The discrepancy in days was caused by the use of the Gregorian calendar in the Low Countries, at a time when England and Scotland still adhered to the Julian calendar.

The epoch of the Christian era is too recent to be a convenient reference point for technical calculations. The French classical scholar Joseph Justus Scaliger proposed in 1583 that the epoch of the Julian era be fixed at January 1, 4713 BCE, at noon. The beginnings of the cycles used in antiquity coincided at that time, and the date was sufficiently remote to furnish a reference point to which all other chronological systems might be compared. The Julian cycle contains 7980 years of 365.25 days, but computation is seldom by years, and the days are numbered consecutively.