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| About site: http://www.math.nus.edu.sg/aslaksen/calendar/islamic.shtml |
Title: Astronomy/Calendars and Timekeeping - The Islamic Calendar The mathematics of the Islamic calendar in Singapore.
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This is sites2007.com cache of m/ as retrieved on 2008.12.02 sites2007.com's cache is the snapshot that we took of the page as we crawled the web. The page may have changed since that time.
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The Islamic Calendar
Astronomers at the Istanbul Observatory
Islamic Astronomy Software
Rules for the Islamic
Calendar in Different Countries
The Islamic Calendar
in Singapore
The Date of Eid ul-Fitr
(Hari Raya Puasa) in 2000
Ramadhan and Eid ul-Fitr
(Hari Raya Puasa) 1420AH/1999-2000CE
Ramadhan and Eid ul-Fitr
(Hari Raya Puasa) 1421AH/2000-2001CE
The Arithmetical
Calendar
Links
Islamic Astronomy Software
The Islamic calendar is based on visibility of the crescent
Moon. This is a very difficult scientific problem. We know perfectly
well where the Moon and the Sun are at any given time, but how light
must the Moon be and how dark must the sky be before we can see the
crescent? And what if the weather is bad?
If you want to get a reasonable estimate for when the Moon
will be visible, the are several nice pieces of software available.
HM Nautical Almanac Observatory in the UK makes very nice lunar visibility charts. Global First Sighting of New Crescent Moon information is given for the last couple of years. The charts for the current
month are also available at Moon Watch.
For many years I have used MoonCalc,
developed
by Dr. Monzur Ahmed. Unfortunately it is a DOS program, and the lunar visibility charts
are done in DOS graphics full screen, so under Windows XP I can
no longer capture screenshots.
The web page of the Islamic Crescents' Observation Project (ICOP) has a number of interesting articles. They also host the software Accurate Times by Mohammad Odeh. It is a Windows program for the Islamic calendar,
Qiblah direction, and prayer times. There are samples of the lunar
visibility charts on Visibility of Ramadan Crescent.
Rules for the Islamic Calendar in Different Countries
In spite of the difficulties, some Muslim communities base their calendar on actual Moon sightings. This is done in India,
Pakistan, Bangladesh and the US.
In Saudi Arabia and most of the Gulf countries they have simplified the calendar. They start the lunar month if the Moon sets after the Sun on the 29th day of the previous month, as seen from Mecca. If you don't believe this, please check out The Actual Saudi Dating System discussion on the web
site of the Islamic Crescents' Observation Project (ICOP).
In Egypt they require moonset to be at least 5 minutes after sunset.
MoonCalc image
The Islamic
Calendar in Singapore
Before 1974, the Muslim calendar in Singapore was based on
sightings from Sultan Shoal, the southernmost part of Singapore.
MUIS (Majlis Ugama Islam Singapura), the Islamic Religious Council
of Singapore, then decided that the new month starts if at sunset
on the eve of the 29th day the Moon is above the horizon. (The Muslim
calendar in Singapore is based on latitude 1 20' 34'' N and longitude
103 51' 08'' E.) In the 80s they decided to follow a variation of
the 1978 Istanbul criteria and require that the altitude of the
Moon should be more than 5 degrees at sunset. In the 90s they switched
to 2 degrees. This was part of an attempt to coordinate the major
holidays with Malaysia, Brunei and Indonesia, which occasionally
may lead to different results.
This is part of the MABIMS criteria, which require that
The altitude of the Moon at sunset is more than 2 degrees.
The arc of light (elongation of the Moon from the Sun or
the apparent angular distance) is more than 3 degrees.
The age of the Moon is more than 8 hours.
In practice, however, MUIS only looks at the first of
the criteria.
MUIS is the sole and final authority on the Muslim calendar
in Singapore. It is very convenient that they use predictions and
let the public know their criteria. Unfortunately, these criteria
are not based on science. The minimum possible values of the three
variables in the MABIMS criteria are approximately:
Altitude > 6
Arc of light > 7
Age > 16
The article Re-evaluation of Hilaal Visibility in Indonesia by Thomas Djamaluddin gives interesting background to the MABIMS
criteria. He looks at 38 reported sightings from religious courts.
He rejects 27 of them because they claimed to have observed the Moon
after the time of moonset or similar problems, but he (somewhat generously
in my opinion) gives the remaining 11 the benefit of doubt.
Islamic
calendar for Singapore by Majlis Ugama Islam Singapura (MUIS), the Islamic Religious Council of Singapore. MUIS seems to move the
location of their calendar around from year to year. If the link
doesn't work, go to their homepage and look under "Downloads" or do a search for Takwim (or Taqwim). This will give you MUIS's prediction for first
visibility of the lunar crescent. But it is based on a dubious
method, so you will often not be able to see the Moon on the day
when MUIS claims that you will.
Astrolabe
by Norman Greene
The Date of Eid ul-Fitr
(Hari Raya Puasa) in 2000
Eid ul-Fitr (Hari
Raya Puasa) was celebrated in Singapore on January 8 2000. To see
why this did not correspond to an actual sighting, you can consult Ramadhan & Eid ul-Fitr 1420AH (1999/2000) by Dr. Monzur Ahmed.
Eid ul-Fitr (Hari
Raya Puasa) was celebrated in Singapore on 27 December 2000. To see
why this did not correspond to an actual sighting, you can consult Ramadhan & Eid ul-Fitr 1421AH (2000CE) by Dr. Monzur Ahmed.
The
Arithmetical Calendar
Some sources describe an arithmetical (tabular) Islamic calendar. It is sometimes used for approximate
conversions for civil purposes, but is not used for religious purposes by Sunnis or Twelver Shi`ites
(Ithna Asharia). However, it is common among Sevener Shi`ites (Isma`ili), including the Bohras (Musta'lis) and Nizaris (Isma`ili Khojas, Aga Khanis). It seems to have been designed to be closer to new Moon than to the first visibility of the lunar crescent, so it often runs a day or two ahead of the regular Islamic calendars.
There are currently about one million Bohras and about 15 millions Nizaris, compared to over a billion Sunnis and close to a hundred
million Twelver Shi`ites. Both of these groups are today primarily Indian Muslim groups, but they trace their history from the Fatimid Caliphate that ruled Egypt from about 970 to 1171. The calendar was put into practice by Imam al-Hakim (985-1021) and is therefore sometimes referred to as the Fatimid or misr (Egyptian) calendar.
The calendar is sometimes attributed to the famous astronomer Al-Battani (850-929) and an alternative version to Ulugh Beg (1393-1449). It is also sometimes
referred to as hisabi. It is possibly also used by the Qadianis (Ahmadiyyas), but they also seem to use a solar calendar, and they are not considered Muslims by other Muslims.
The average lunar year is about 354 11/30 days, so you get a reasonable lunar calendar by using a cycle
of 11 leap years (kasibah) with 355 days in a 30 year cycle. The odd numbered months have 30 days and the even numbered months have
29 days, except in a leap year when the 12th and final month has 30 days. There are several versions for how to space out the 11 leap years. The most common rule is the one followed by the Nizaris Isma`ili, which uses years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, 29, but some replace 16 by 15 and the Bohras replace 7 by 8, 18 by 19 and 26
by 27. Imran Hussain has both a Bohra and a Sunni version of his Islamic Diary. For more information about the different leap year rules, see Islamic-Western Calendar Converter (Based on the Arithmetical or Tabular Calendar) by Robert H. van Gent.
Links
Undergraduate research project on Lunar
Visibility and the Islamic Calendar by my student Leong Wen Xin.
Notes for lecture on How
Does the Islamic Calendar Really Work in Different Parts of the
World? at the AMS/MAA meeting in Atlanta 2005.
Moonsighting.com by Khalid Shaukat.
Dr. Monzur Ahmed is the author of MoonCalc, which for many years was the leading lunar visibility and Islamic calendar software. He has
pages on Astronomy and Islam and Ramadhan (Ramadan) and Eid-al-Fitr.
The web page of the Islamic Crescents' Observation Project (ICOP) has a number of interesting articles. They also host the software Accurate Times by Mohammad Odeh. It is a Windows program for the Islamic calendar,
Qiblah direction, and prayer times. There are samples of the lunar
visibility charts on Visibility of Ramadan Crescent. Their page on The Actual Saudi Dating System will probably surprise many.
Islamic
calendar for Singapore by Majlis Ugama Islam Singapura (MUIS), the Islamic Religious Council of Singapore. MUIS seems to move the
location of their calendar around from year to year. If the link
doesn't work, go to their homepage and look under "Downloads" or do a search for Takwim (or Taqwim). This will give you MUIS's prediction for first
visibility of the lunar crescent. But it is based on a dubious
method, so you will often not be able to see the Moon on the day
when MUIS claims that you will.
Islamsk Råd Norge, Hilalkomiteen (in Norwegian) and Islamsk Råd Norge, Hilalkomiteen (alternative site) explain the policies of the Islamic Council of Norway.
HM Nautical Almanac Observatory in the UK makes very nice lunar visibility charts. Their Websurf contains a wealth of information, including Global First Sighting of New Crescent Moon information for the last couple of years. The charts for the current
month are also available at Moon Watch.
Moon Watch.
Crescent
Moon Visibility and the Islamic Calendar from the Astronomical Applications Department of the U.S. Naval Observatory.
Moon
Research Centre (U.K). The article on Policies Adopted in Britain by Muslims in Celebrating Islamic Festivals is essential reading! They also have a copy of the RGO Astronomical Information Sheet No. 6.
Predicting the First Visibility of the Lunar Crescent, The
Umm al-Qura Calendar of Saudi Arabia, Islamic-Western Calendar Converter (Based on the Arithmetical or Tabular Calendar) and Internet sites over de islamitische tijdrekening (in Dutch) by Robert H. van Gent.
Crescent-Sighting
and Islamic Calendars and Islamic Astronomy: Questions, Comments and Correspondence by David McNaughton.
I have a separate page of additional calendar links.
Back to Helmer
Aslaksen's page on Calendars in Singapore.
Helmer
Aslaksen
Department
of Mathematics
National
University of Singapore
aslaksen@math.nus.edu.sg
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The Islamic Calendar 2008 December
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The mathematics of the Islamic calendar in Singapore.
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