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The Islamic calendar or Muslim calendar or Hijri calendar (Template:Lang-ar; at-taqwīm al-hijrī; Persian: تقویم هجری قمری ‎ taqwīm-e hejri-ye qamari; Template:Lang-tr; Template:Lang-ur Islami taqwīm; Malay: Takwim Hijrah) is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to date events in many Muslim countries (concurrently with the Gregorian calendar), and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days and festivals. The first year was the year during which the emigration of the Islamic prophet Muhammad from Mecca to Medina, known as the Hijra, occurred. Each numbered year is designated either H for Hijra or AH for the Latin anno Hegirae (in the year of the Hijra). A limited number of years before Hijra (BH) are used to date events related to Islam, such as the birth of Muhammad in 53 BH. The current Islamic year is 1431 AH, from approximately 18 December 2009 (evening) to 6 December 2010 (evening).

Being a purely lunar calendar, it is not synchronized with the seasons. With an annual drift of 11 or 12 days, the seasonal relation is repeated approximately each 33 Islamic years.

Months

The Islamic months are named as follows:

1. Muḥarram محرّم (or Muḥarram al Ḥaram)
2. Ṣafar صفر (or Ṣafar al Muzaffar)
3. Rabīʿ al-Awwal (Rabīʿ I) ربيع الأوّل
4. Rabīʿ al-Thānī (or Rabīʿ al-Ākhir) (Rabīʿ II) ربيع الآخر أو ربيع الثاني
5. Jumādā al-Ūlā (Jumādā I) جمادى الأولى
6. Jumādā al-Thānī (or Jumādā al-Ākhirah) (Jumādā II) جمادى الآخرة أو جمادى الثانية
7. Rajab رجب (or Rajab al-Murājab)
8. Shaʿbān شعبان (or Shaʿbān al-Muʿaẓẓam)
9. Ramaḍān رمضان (or Ramaḍān al-Mubārak)
10. Shawwāl شوّال (or Shawwāl al-Mukarram)
11. Dhū al-Qaʿda ذو القعدة (or Dhū al-Qiʿda)
12. Dhū al-Ḥijja ذو الحجة (or Dhū al-Ḥajja)

Of all the months in the Islamic calendar, Ramadan is the most venerated. Muslims are required to abstain from eating, drinking any liquid, and sexual intercourse during the daylight hours of this month.

Days of the week

In the Arabic language, as in the Hebrew language, the "first day" of the week corresponds with Sunday of the planetary week. The Islamic and Jewish weekdays begin at sunset, whereas the medieval Christian and planetary weekdays begin at the following midnight. Muslims gather for worship at a mosque at noon on "gathering day" (Yaum al-Jumu'ah) which corresponds with Friday ("yawm يوم" means day). Thus "gathering day" is often regarded as the weekly day of rest, so the following day, Saturday, is often regarded as the first day of the work week.

History

Pre-Islamic calendar

Some scholars, both Muslim and Western, think that the pre-Islamic calendar of central Arabia was a purely lunar calendar similar to the modern Islamic calendar, differing only when the sanctity of the four holy months were postponed by one month from time to time.

Other scholars, both Muslim and Western, concur that it was originally a lunar calendar, but about 200 years before the Hijra it was transformed into a lunisolar calendar containing an intercalary month added from time to time to keep the pilgrimage within the season of the year when merchandise was most abundant for Bedouin buyers. This intercalation was administered by the Nasa'a of the tribe Kinana, known as the Qalāmis, the plural of Qalammas, who learned of it from Jews. The process was called Nasi or postponement because every third year the beginning of the year was postponed by one month. The intercalation doubled the month of the pilgrimage, that is, the month of the pilgrimage and the following month were given the same name, postponing the names and the sanctity of all subsequent months in the year by one. The first intercalation doubled the first month Muharram, then three years later the second month Safar was doubled, continuing until the intercalation had passed through all twelve months of the year and returned to Muharram, when it was repeated. Support for this view is provided by inscriptions from the south Arabian pre-Islamic kingdoms of Qataban (Kataban) and Sheba (Saba) (both in modern Yemen), whose lunisolar calendars featured an intercalary month obtained by repeating a normal month. The prohibition of Nasi was revealed when the intercalated month had returned to its position just before Nasi began.

If Nasi meant intercalation, then the number and the position of the intercalary months between 1 AH and 10 AH are uncertain, western calendar dates commonly cited for key events in early Islam such as the Hijra, the Battle of Badr, the Battle of Uhud and the Battle of the Trench, should be viewed with caution as they might be in error by one, two or even three lunar months.

Prohibiting Nasi

In the tenth year of the Hijra, as documented in the Qur'an (sura 9:36-37), Muslims believe God (Allah) revealed the prohibition of the Nasi.

The number of months with Allah has been twelve months by Allah's ordinance since the day He created the heavens and the earth. Of these four are known as forbidden ; That is the straight usage, so do not wrong yourselves therein, and fight those who go astray. But know that Allah is with those who restrain themselves.

Verily the transposing (of a prohibited month) is an addition to Unbelief: The Unbelievers are led to wrong thereby: for they make it lawful one year, and forbidden another year, of months forbidden by Allah and make such forbidden ones lawful. The evil of their course seems pleasing to them. But Allah guideth not those who reject Faith.

This prohibition was repeated by Muhammad during the farewell sermon which was delivered on 9 Dhu al-Hijja 10 AH on Mount Arafat during the farewell pilgrimage to Mecca.

Certainly the Nasi is an impious addition, which has led the infidels into error. One year they authorise the Nasi, another year they forbid it. They observe the divine precept with respect to the number of the sacred months, but in fact they profane that which God has declared to be inviolable, and sanctify that which God has declared to be profane. Assuredly time, in its revolution, has returned to such as it was at the creation of the heavens and the earth. In the eyes of God the number of the months is twelve. Among these twelve months four are sacred, namely, Rajab, which stands alone, and three others which are consecutive.

— translated by Sherrard Beaumont Burnaby

The three successive forbidden months mentioned by Muhammad (months in which battles are forbidden) are Dhu al-Qi'dah, Dhu al-Hijjah, and Muharram, months 11, 12, and 1. The single forbidden month is Rajab, month 7. These months were considered forbidden both within the new Islamic calendar and within the old pagan Meccan calendar, although whether they maintained their "forbidden" status after the conquest of Mecca has been disputed among Islamic scholars.

The prohibition on the Nasi has not affected the creation of new purely solar calendars in the Muslim world; the modern Iranian calendar is a solar calendar dated from the Hijra, with eight intercalated leap days in a 33-year cycle.

Numbering the years

In pre-Islamic Arabia, it was customary to identify a year after a major event which took place in it. Thus, according to Islamic tradition, Abraha, governor of Yemen, then a province of the Christian Kingdom of Aksum (Ethiopia), attempted to destroy the Kaaba with an army which included several elephants. The raid was unsuccessful, but that year became known as the Year of the Elephant. It saw the birth of Muhammad (see surat al-Fil). That corresponded to the year 570 or 571 CE, though many western scholars say the expedition of Abraha was in fact much earlier.

In 638 (the year 17 AH), Abu-Musa al-Asha'ari, one of the officials of the second Caliph Umar in Basrah, complained about the absence of any dating system in the correspondence he received from Umar, making it difficult for him to determine which instructions were most recent. This report convinced Umar of the need to introduce a calendar system for Muslims. After debating the issue with his Counsellors, he decided to start the calendar with the date of Muhammad's arrival at Madina tun Nabi (known as Yathrib, before Muhammad's arrival).

Uthman ibn Affan then suggested to start the calendar with the month of Muharram, in line with the established custom of the Arabs at that time.

The Islamic calendar numbering of the years thus began with the month of Muharram in the year of Muhammad's arrival at the city of Medina. According to calculations, the first day of the first year corresponded to Friday, July 16, 622 (even though the actual emigration took place in September). Because of the Hijra event, the calendar was named the Hijra calendar.

Though Cook and Crone in "Hagarism" cite a coin form 17 AH, the first surviving attested use of a Hijri calendar date alongside a Coptic calendar date is on a papyrus from Egypt in 22 AH, PERF 558.

Astronomical considerations

The Islamic calendar is not to be confused with a lunar calendar that is based on astronomical calculations. The latter is based on a year of 12 months adding up to 354.37 days. Each lunar month begins at the time of the monthly "conjunction", when the Moon is located on a straight line between the Earth and the Sun. The month is defined as the average duration of a rotation of the Moon around the Earth (29.53 days). By convention, months of 30 days and 29 days succeed each other, adding up over two successive months to 59 full days. This leaves only a small monthly variation of 44 mn to account for, which adds up to a total of 24 hours (i.e. the equivalent of one full day) in 2.73 years. To settle accounts, it is sufficient to add one day every three years to the lunar calendar, in the same way that one adds one day to the Gregorian calendar, every four years. The technical details of the adjustment are described in Tabular Islamic Calendar.

The Islamic calendar, however, is based on a different set of conventions. Each month has either 29 or 30 days, but usually in no discernible order. Traditionally, the first day of each month is the day (beginning at sunset) of the first sighting of the hilal shortly after sunset. If the hilal is not observed immediately after the 29th day of a month (either because clouds block its view or because the western sky is still too bright when the moon sets...), then the day that begins at that sunset is the 30th. Such a sighting has to be made by one or more trustworthy men testifying before a committee of Muslim leaders. Determining the most likely day that the hilal could be observed was a motivation for Muslim interest in astronomy, which put Islam in the forefront of that science for many centuries.

This traditional practice is still followed in the overwhelming majority of Muslim countries. Each Islamic State proceeds with its own monthly observation of the new moon (or, failing that, awaits the completion of 30 days) before declaring the beginning of a new month on its territory. But, the lunar crescent becomes visible only some 15–18 hours after the conjunction, and only subject to the existence of a number of favourable conditions relative to weather, time, geographic location, as well as various astronomical parameters. Given the fact that the moon sets progressively later than the sun as one goes West, Western Muslim countries are likely to observe the new moon one day earlier than Eastern Muslim countries. Due to the interplay of all these factors, the beginning of each month differs from one Muslim country to another, and the information provided by the calendar in any country does not extend beyond the current month.

A number of Muslim countries try to overcome some of these difficulties by applying different astronomy-related rules to determine the beginning of months. Thus, Malaysia, Indonesia, and a few others begin each month at sunset on the first day that the moon sets after the sun (moonset after sunset). In Egypt, the month begins at sunset on the first day that the moon sets at least five minutes after the sun...A detailed analysis of the available data shows, however, that there are major discrepancies between what countries say they do on this subject, and what they actually do.

Theological considerations

If the Islamic calendar were prepared using astronomical calculations, Muslims throughout the Muslim world could use it to meet all their needs, the way they use the Gregorian calendar today. But, there are divergent views on whether it is licit to do so.

A majority of theologians oppose the use of calculations on the grounds that the latter would not conform with Muhammad's recommendation to observe the new moon of Ramadan and Shawal in order to determine the beginning of these months.

But, some jurists see no contradiction between Muhammad's teachings and the use of calculations to determine the beginnings of lunar months. They consider that Muhammad's recommendation was adapted to the culture of the times, and should not be confused with the acts of worship.

Thus, jurists Ahmad Muhammad Shakir and Yusuf al-Qaradawi both endorsed the use of calculations to determine the beginning of all months of the Islamic calendar, in 1939 and 2004 respectively. So did the "Fiqh Council of North America" (FCNA) in 2006 and the "European Council for Fatwa and Research" (ECFR) in 2007.

Saudi Arabia's Umm al-Qura calendar

Saudi Arabia uses the sighting method to determine the beginning of each month of the Hijri calendar. Since AH 1419 (1998/99) several official hilal sighting committees have been set up by the government to determine the first visual sighting of the lunar crescent at the beginning of each lunar month. Nevertheless, the religious authorities also allow the testimony of less experienced observers and thus often announce the sighting of the lunar crescent on a date when none of the official committees could see it.

The country also uses the Umm al-Qura calendar, based on astronomical calculations, but this is restricted to administrative purposes. The parameters used in the establishment of this calendar underwent significant changes over the past decade.

Before AH 1420 (before April 18, 1999), if the moon's age at sunset in Riyad was at least 12 hours, then the day ending at that sunset was the first day of the month. This often caused the Saudis to celebrate holy days one or even two days before other predominantly Muslim countries, including the dates for the Hajj, which can only be dated using Saudi dates because it is performed in Mecca.

For AH 1420-22, if moonset occurred after sunset at Mecca, then the day beginning at that sunset was the first day of a Saudi month, essentially the same rule used by Malaysia, Indonesia, and others (except for the location from which the hilal was observed).

Since the beginning of AH 1423 (March 16, 2002), the rule has been clarified a little by requiring the geocentric conjunction of the sun and moon to occur before sunset, in addition to requiring moonset to occur after sunset at Mecca. This ensures that the moon has moved past the sun by sunset, even though the sky may still be too bright immediately before moonset to actually see the crescent.

In 2007, the Islamic Society of North America, the Fiqh Council of North America and the European Council for Fatwa and Research announced that they will henceforth use a calendar based on calculations, using the same parameters as the Umm al-Qura calendar, to determine (well in advance) the beginning of all lunar months (and therefore the days associated with all religious observances). This was intended as a first step on the way to unify Muslims' calendars throughout the world, in some future time. But, despite this stated objective, they will continue to differ, on this point, from Saudi Arabia's officially stated, but hard to verify policy of relying exclusively on sighting to determine the dates of religious observances.

Tabular Islamic calendar

There exists a variation of the Islamic calendar known as the tabular Islamic calendar in which months are worked out by arithmetic rules rather than by observation or astronomical calculation. It has a 30-year cycle with 11 leap years of 355 days and 19 years of 354 days. In the long term, it is accurate to one day in about 2500 years. It also deviates up to about 1 or 2 days in the short term.

Kuwaiti algorithm

Microsoft uses the "Kuwaiti algorithm", a variant of the tabular Islamic calendar, to convert Gregorian dates to the Islamic ones. Microsoft claims that the variant is based on a statistical analysis of historical data from Kuwait.

Notable dates

Important dates in the Islamic (Hijri) year are:

• 1 Muharram (Islamic New Year)
• 10 Muharram (Day of Ashura) For Sunni Muslims, the crossing of the Red Sea by the Israelites. For Shia Muslims, the martyrdom of Husayn ibn Ali, the grandson of Muhammad, and his followers.
• 12 Rabi al Awal (Mawlid an Nabi for Sunni Muslims)
• 17 Rabi al Awal (Mawlid an Nabi for Shia Muslims Twelvers)
• 13 Rajab (Birthday of Ali ibn Abi Talib.)
• 27 Rajab (Isra and Miraj)
• 15 Sha'ban (Mid-Sha'ban, or Night of Forgiveness), and the birthday of Muhammad al-Mahdi (The Twelfth Imam)
• 1 Ramadan (first day of fasting)
• 21 Ramadan Ali ibn Abi Talib's Martyrdom.
• 27 Ramadan (Nuzul Al-Qur'an) (17 Ramadan in Indonesia and Malaysia)
• Last third of Ramadan which includes Laylat al-Qadr
• 1 Shawwal (Eid al-Fitr)
• 8-13 Dhu al-Hijjah (the Hajj to Mecca)
• 10 Dhu al-Hijjah (Eid al-Adha)
• 18 Dhu al-Hijjah (Eid al-Ghadeer)
• 24 Dhu al-Hijjah (Eid al-Mubahila)

Convert Hijri to Gregorian year or Gregorian to Hijri year

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To convert from a Hijri year to a Gregorian year:

G = 0.97023×H + 621.57

To convert from a Gregorian year to a Hijri year:

H = (G − 621.57)/0.97023

The simplest way to convert a Muslim date to its corresponding civil date is through the Jewish calendar. Theoretically, the months in both calendars start on the same day if the displacements which are a feature of the Jewish system are ignored. The table below gives, for nineteen years, the Muslim month which corresponds to the first Jewish month.

This table may be extended since every nineteen years the Muslim month number increases by seven. When it goes above twelve, subtract twelve and add one to the year AH.

Example calculation

What is the civil date and year AH of the first day of the first month in the year AD20875?

We first find the Muslim month number corresponding to the first month of the Jewish year which begins in AD20874. Dividing 20874 by 19 gives quotient 1098 and remainder 12. Dividing 2026 by 19 gives quotient 106 and remainder 12. The two years are therefore (1098-106)=992x19 years apart. The Muslim month number corresponding to the first Jewish month is therefore (992x7)=6944 higher than in 2026. To convert into years and months divide by twelve - 6944/12=578 years and 8 months. Adding, we get 1447y 10m + 20874y - 2026y + 578y 8m = 20874y 6m. Therefore, the first month of the Jewish year beginning in AD20874 corresponds to the sixth month of the Muslim year AH20874. The worked example in Hebrew calendar#Conversion between Jewish and civil dates shows that the civil date of the first day of this month (ignoring the displacements) is Friday, 14th June. The year AH20875 will therefore begin seven months later, on the first day of the eighth Jewish month, which the worked example shows to be 7th January, AD20875 (again ignoring the displacements).

A reading of the section which follows will show that the year AH20875 is wholly contained within the year AD20875, also that in the Gregorian calendar this correspondence will occur one year earlier. The reason for the discrepancy is that the Gregorian year (like the Julian) is slightly too long, so the Gregorian date for a given AH date will be earlier and the Muslim calendar catches up sooner.

Current correlations

An Islamic year will be entirely within a Gregorian year of the same number in the year 20874, after which year the number of the Islamic year will always be greater than the number of the concurrent Gregorian year. The Islamic calendar year of 1429 occurred entirely within the Gregorian calendar year of 2008. Such years occur once every 33 or 34 Islamic years (32 or 33 Gregorian years). More are listed here:

Because a hijri or Islamic lunar year is between 10 and 12 days shorter than a Gregorian year, it begins 10–12 days earlier in the Gregorian year following the Gregorian year in which the previous hijri year began. Once every 33.58 hijri years, or once every 32.58 Gregorian years, the beginning of a hijri year (1 Muharram) coincides with one of the first ten days of January. Subsequent hijri New Years move backward through the Gregorian year back to the beginning of January again, passing through the entire year.

Uses

The Islamic calendar is now used primarily for religious purposes, and for official dating of public events and documents in Muslim countries. Because of its nature as a purely lunar calendar, it cannot be used for agricultural purposes and historically Islamic communities have used other calendars for this purpose: the Egyptian calendar was formerly widespread in Islamic countries, and the Iranian calendar and the 1789 Ottoman calendar (a modified Julian calendar) were also used for agriculture in their countries. In Morocco, the Berber calendar (another Julian calendar) is still used by farmers in the countryside. These local solar calendars have receded in importance with the near-universal adoption of the Gregorian calendar for civil purposes. As noted above, Saudi Arabia uses the Islamic calendar to date religious occasions such as Ramadan, Hajj, etc. and the Umm-al-Qura calendar, based on calculations, for administrative purposes and daily government business.

See also

• Javanese calendar
• Iranian calendar
• 1 AH
• Lunar phase

References

1. ^ Watt, W. Montgomery. "Hidjra". In P.J. Bearman, Th. Bianquis, C.E. Bosworth, E. van Donzel and W.P. Heinrichs (ed.). Encyclopaedia of Islam Online. Brill Academic Publishers. ISSN 1573-3912.{{cite encyclopedia}}: CS1 maint: multiple names: editors list (link)
2. Prophet Muhammad by Islamic Finder
3. B. van Dalen. "Tarikh". In P.J. Bearman, Th. Bianquis, C.E. Bosworth, E. van Donzel and W.P. Heinrichs (ed.). Encyclopedia of Islam Online. Brill Academic Publishers. ISSN 1573-3912. {{cite encyclopedia}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: multiple names: editors list (link)
4. Trawicky (2000) p. 232
5. Mahmud Effendi (1858), as discussed by Burnaby, pages 460–470.
6. According to "Tradition", repeatedly cited by F.C. De Blois.
7. F.C. De Blois, "TA'RIKH": I.1.iv. "Pre-Islamic and agricultural calendars of the Arabian peninsula", The Encyclopaedia of Islam X:260.
8. al-Biruni, "Intercalation of the Ancient Arabs", The Chronology of Ancient Nations, tr. C. Edward Sachau, (London: William H. Allen, 1000/1879) 13–14, 73–74.
9. Abu Ma'shar al-Balkhi (787–886), Kitab al-Uluf, Journal Asiatique, series 5, xi (1858) 168+. Template:Fr icon Template:Ar icon
10. A. Moberg, "NASI'", The Encyclopaedia of Islam VII:977.
11. A. Moberg, "NASI'", E.J. Brill's first encyclopaedia of Islam
12. From an illustrated manuscript of Al-Biruni's 11th c. Vestiges of the Past (Bibliothèque Nationale, Paris, Arabe 1489 fol. 5v. (Bibliothèque Nationale on-line catalog Mandragore
13. Sherrard Beaumont Burnaby, Elements of the Jewish and Muhammadan calendars (London: 1901) 370.
14. Appreciating Islamic History (Microsoft Word document, 569KB)
15. Emile Biémont, Rythmes du temps, Astronomie et calendriers, De Borck, 2000, 393p
16. Khalid Chraibi: Issues in the Islamic Calendar, Tabsir.net
17. Karim Meziane et Nidhal Guessoum : La visibilité du croissant lunaire et le ramadan, La Recherche n° 316, janvier 1999, pp. 66–71
18. Moonsighting.com - Methods for beginning of Islamic months in different countries
19. Allal el Fassi : « Aljawab assahih wannass-hi al-khaliss ‘an nazilati fas wama yata’allaqo bimabda-i acchouhouri al-islamiyati al-arabiyah », " and the beginning of Islamic Arab months", report prepared at the request of King Hassan II of Morocco, Rabat, 1965 (36 p.), with no indication of editor.
20. Muhammad Mutawalla al-Shaârawi : Fiqh al-halal wal haram (edited by Ahmad Azzaâbi), Dar al-Qalam, Beyrouth, 2000, p. 88.
21. Some theologians also interpret Surah al-Baqarah 2:185 as requiring direct sighting, but they represent only a minority. The Quranic verse reads as follows : "185. The month of Ramadân in which was revealed the Qur'ân, a guidance for mankind and clear proofs for the guidance and the criterion (between right and wrong). So whoever of you sights (the crescent on the first night of) the month (of Ramadân i.e. is present at his home), he must observe Saum (fasts) that month, and whoever is ill or on a journey, the same number from other days. God intends for you ease, and He does not want to make things difficult for you. (He wants that you) must complete the same number (of days), and that you must magnify God for having guided you so that you may be grateful to Him."
22. Interpretation of the Meaning of The Noble Quran Translated into the English Language By Dr. Muhammad Taqi-ud-Din Al-Hilali Ph.D. & Dr. Muhammad Muhsin Khan
23. Abderrahman al-Haj : « The faqih, the politician and the determination of lunar months » (in arabic)
24. Allal el Fassi : "Aljawab assahih..." op. cit.
25. The dynasty of Fatimids in Egypt used a tabular pre-calculated calendar over a period of two centuries, between the 10th and 12th centuries, before a change of political regime reactivated the procedure of observation of the new moon.
26. Helmer Aslaksen: The Islamic calendar
27. Ahmad Shakir : « The beginning of arab months … is it legal to determine it using astronomical calculations? » (published in arabic in 1939) reproduced in the Arab daily « Al-Madina », 13 october 2006 (n° 15878)
28. Yusuf al-Qaradawi : « Astronomical calculations and determination of the beginning of months » (in arabic)
29. For a detailed discussion of Shakir's legal opinion on the subject, see "Issue N° 9" in Khalid Chraibi: Issues in the Islamic Calendar, Tabsir.net
30. Fiqh Council of North America Islamic lunar calendar
31. Zulfikar Ali Shah The astronomical calculations: a fiqhi discussion
32. Islamic Center of Boston, Wayland
33. For a detailed discussion of the issues and the FCNA and ECFR positions, see : Khalid Chraibi: Can the Umm al Qura calendar serve as a global Islamic calendar? Tabsir.net
34. Template:PDFlink
35. Ramadan and Eid announcement by the Fiqh Council of North America (revised)
36. Khalid Chraibi : Can the Umm al Qura calendar serve as a global Islamic calendar?
37. The "Kuwaiti Algorithm" (Robert van Gent)
38. Hijri Dates in SQL Server 2000
39. Glassé, Cyril (2001). The New Encyclopedia of Islam, pp. 98-99. Rowman Altamira. ISBN 0759101906.

External links

• (Prayer Times for Cities the Worldover)
• UrduCalendar.com (Islamic_Gregorian calendar) website
• Moonsighting.com website
• Helmer Aslaksen: The Islamic calendar
• Moonsighting.com: Selected articles on the Islamic calendar
• Islamic Crescent’s Observation Project (ICOP): Selected articles on the Islamic calendar
• Mohammad Ilyas Lunar crescent visibility criterion and Islamic calendar
• Mohamed Odeh: The actual Saudi dating system
• van Gent: The Umm al-Qura Calendar of Saudi Arabia
• van Gent: The Islamic Calendar of Turkey
• van Gent: Predicting the First Visibility of the Lunar Crescent (includes a comprehensive bibliography on lunar crescent visibility)
• Ahmad Shakir: « The beginning of Arab months … is it licit to determine it using astronomical calculations? » (published in Arabic in 1939) reproduced by the daily « Al-Madina », October 13, 2006 (n° 15878)
• Yusuf al-Qaradawi: « Astronomical calculations and determination of the beginning of months » (in Arabic)
• Abderrahman al-Haj: « The faqih, the politician and the determination of lunar months » (in Arabic)
• Fiqh Council of North America: Islamic lunar calendar decision of 2006
• Islamic Center of Boston, Wayland: Moonsighting Decision documents
• Zulfikar Ali Shah The astronomical calculations: a fiqhi discussion
• Khalid Chraibi: Issues in the Islamic Calendar, Tabsir.net
• Khalid Chraibi: Towards a global Islamic calendar, SaudiDebate.com
• Khalid Chraibi: Can the Umm al Qura calendar serve as a global Islamic calendar? Tabsir.net
• Khalid Chraibi: La charia et le calendrier (Shari'ah and the calendar) Oumma.com
• Islamic Months - Significance and Blessed Months
• Hijri Calendar
• Correspondence between Hebrew and Islamic calendars, months and holidays (pdf)
• HilalSighting.org website

Date converters

• Gregorian-Hijri Dates Converter (and vice-versa)
• Islamic-Western Calendar Converter (Based on the Arithmetical or Tabular Calendar)
• al-Islam.com date converter
• Hijri Calendar Gadget Persian/Islamic/Gregorian Calendar Gadget for Windows Vista Sidebar with Persian Occasions. Powerful Converter with Occasions.
• Remotely hosted Gregorian-Hijri calendar
• Link To Islam - Hijri to Gregorian and Gregorian to Hijri Date Converter

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Time in physics	Absolute space and time Spacetime Chronon Continuous signal Coordinate time Cosmological decade Discrete time and continuous time Proper time Theory of relativity Time dilation Gravitational time dilation Time domain Time-translation symmetry T-symmetry
Horology	Clock Astrarium Atomic clock Complication History of timekeeping devices Hourglass Marine chronometer Marine sandglass Radio clock Watch stopwatch Water clock Sundial Dialing scales Equation of time History of sundials Sundial markup schema
Calendar	Gregorian Hebrew Hindu Holocene Islamic (lunar Hijri) Julian Solar Hijri Astronomical Dominical letter Epact Equinox Intercalation Julian day Leap year Lunar Lunisolar Solar Solstice Tropical year Weekday determination Weekday names
Archaeology and geology	Chronological dating Geologic time scale International Commission on Stratigraphy
Astronomical chronology	Galactic year Nuclear timescale Precession Sidereal time
Other units of time	Instant Flick Shake Jiffy Second Minute Moment Hour Day Week Fortnight Month Year Olympiad Lustrum Decade Century Saeculum Millennium
Related topics	Chronology Duration music Mental chronometry Decimal time Metric time System time Time metrology Time value of money Timekeeper

• Hijri dates
• Islamic calendar