Islamic months begin at sunset on the day of visual sighting of the lunar crescent. Even though visual sighting is necessary to determine the start of a month, it is useful to accurately predict when a crescent is likely to be visible in order to produce lunar calendars in advance. Although it is possible to calculate the position of the moon in the sky with high precision, it is often difficult to predict if a crescent will be visible from a particular location. Visibility depends on a large number of factors including weather condition, the altitude of the moon at sunset, the closeness of the moon to the sun at sunset, the interval between sunset and moonset, atmospheric pollution, the quality of the eyesight of the observer, use of optical aids etc. Since ancient times, many civilisations and astronomers have tried to predict the likelihood of visualising the new moon using different 'minimum visibility criteria'. However, all these criteria are subject to varying degrees of uncertainty.
The subject of crescent visibility has been studied in modern times by Prof. Ilyas in Malaysia who has developed several visibility criteria and the concept of the International Lunar Date Line (ILDL). Ilyas's main criterion depends on the moon's altitude (in degrees) above the horizon at sunset and the moon's angular distance from the sun (relative azimuth) at sunset. If a moon's altitude and relative azimuth are greater than certain threshold values, then the moon is likely to be visible. The ILDL is a curved line on a world map which separates areas (west of the line) where the crescent is likely to be seen at the start of the lunar month from areas (east of the line) where the crescent is unlikely to be seen. The probability of sighting the crescent increases as one travels west of the ILDL and diminishes as one travels east of the ILDL. Unlike the solar date line which has a fixed position, the position of the ILDL moves from month to month.
A computer program called MoonCalc by Dr. Monzur Ahmed was used to search the world for locations which satisfy Ilyas's altitude/relative azimuth criterion at the start of a lunar month. On the basis of this scan, world maps for the start of each lunar month were drawn showing areas where the crescent is likely to be seen first. The different coloured bands represent the age of the moon at sunset on the day of predicted sighting. MoonCalc has many other features and also supports several other crescent sighting criteria.
With the maps below:
Dates on the left of the map indicate earliest predicted crescent visibility for shaded areas of the map
Dates on the right of the map indicate earliest predicted crescent visibility for unshaded areas
The 1st day of the Islamic month occurs on the day after crescent sighting - for each month, two dates are given depending on the location. The first date applies for the shaded areas, the second date for the unshaded areas.
Click thumbnails of maps to see full-sized maps
Muharram starts 17
or 18 April 1999
Conjunction: 16 April 1999, 04:23 TD
16 April 
17
April
Safar starts (16 or)
17 May 1999
Conjunction: 15 May 1999, 12:06 TD
15 May 
16
May
Rabi Al-Awwal starts
15 or 16 June 1999
Conjunction: 13 June 1999, 19:04 TD
14 June 
15
June
Rabi Al-Thani starts
(14 or) 15 July 1999
Conjunction: 13 July 1999, 02:25 TD
13 July 
14
July
Jumad Al-Ula starts
13 (or 14) August 1999
Conjunction: 11 August 1999, 11:10 TD
12 Aug 
13
Aug
Jumad Al-Thani
starts 11 or 12 September 1999
Conjunction: 9 September 1999, 22:03 TD
10 Sep 
11
Sep
Rajab starts 11 (or
12) October 1999
Conjunction: 9 October 1999, 11:36 TD
10 Oct 
11
Oct
Sha'ban starts (9)
or 10 November 1999
Conjunction: 8 November 1999, 03:54 TD
8 Nov 
9
Nov
Ramadhan starts 9 or
10 December 1999
Conjunction: 7 December 1999, 22:33 TD
8 Dec 
9
Dec
Shawwal starts 8 or
9 January 2000
Conjunction: 6 January 2000, 18:15 TD
7 Jan 
8
Jan
Zul-Qida starts 7
(or 8) Feb 2000
Conjunction: 5 February 2000, 13:04 TD
6 Feb 
7
Feb
Zul-Hijja starts (7
or) 8 March 2000
Conjunction: 6 March 2000, 05:18 TD
6 March 
7
March
Muharram starts 6 or
7 April 2000
Conjunction: 4 April 2000, 18:13 TD
5 April 
6
April
Please note :
Conjunction (astronomical new moon) is used to describe the time of the birth of a new moon when the earth, sun and moon are in the same plane. Conjunction is NOT the same as visible new moon. Usually the moon has to be at least 15 hours old before it can be seen from somewhere on earth. Conjunction times are given in Terrestrial Dynamical Time (TD). TD is a uniform time scale based on the atomic clock and is not influenced by the earth's irregular and unpredictable rotation (unlike GMT and Universal Time). TD tends to be favoured by astronomers for accurate work.
Copyright © by Dr. Monzur Ahmed. Last updated: 2nd May 1999
