Visibility of Crescents in 1998

Astronomical Calculations of Crescents
& Determination of The Beginning of Islamic Months

The Moon orbits Earth once every 29.53 days (average of synodic month). Because of this revolution, phases of the Moon change as the Moon's position change relative to the Earth and the Sun. So, during the Moon's orbit, if the Moon, Earth and the Sun lie exactly at the same line and the Moon in the middle, the Sun will illuminate half of the Moon that faces it, and the other half which faces us, will be dark because it does not reflect rays of the Sun (However, due to the inclination of the Moon that might reach up to 6 degrees, it may reflect a very small percentage of Sun's rays, but according to my information no observer yet reported seeing such crescent) . At this point, the Moon is called Wane or New Moon. After that, the Moon continues orbiting the Earth and begins to reflect a small amount of Sun's rays and now we see the Moon as a very small waxing crescent. Afterwards, it becomes first quarter, full Moon, last quarter, waning crescent and then wane again.

Moon's age is measured from the moment of the wane (New Moon). We often say this Full Moon is 14 days old, which means that the number of days since the wane is 14. And we say this crescent is about 2-3 days old. But, did any one ask himself what is the minimum age of crescent that we can see ? Generally, through a telescope, it is not likely to see a crescent that is less than 10 hours, i.e. if we want to observe the thin waxing crescent to determine the beginning of an Arabic month, the Moon must be in the wane phase (New Moon) 10 hours ago or more. But why?!
The wane Moon (New Moon) is located exactly at the Sun's direction, so the Sun's glare will prevent us from seeing it, in addition, the percentage of the reflected rays out of the wane Moon (New Moon) is equal to zero, and this percentage increases as the Moon's age increases. Thus, GENERALLY human eye through a telescope can't detect any reflected rays from the Moon if the Moon's age is less than about 10 hours.

* When to Locate the Waxing Crescent?

The new waxing crescent is located near the Sun, so we shall wait until Sunset, because it is obviously impossible to observe the thin waxing crescent before Sunset. In addition, we must wait a reasonable time until the twilight decreases, i.e. until we can differentiate between Moon's light and twilight glare, a 10-minute period could be enough sometimes to detect the thin waxing crescent.

* Where to Locate the Waxing Crescent?

As mentioned above, the wane Moon (New Moon) is located exactly near the Sun. If we assume that the Moon will set when it is wane (New Moon), generally it will set along with the Sun, but we are looking for a crescent of 10 hours old, which means that it is still near the Sun. So, we must look at the west, a little bit over the Sunset point.

* When the Waxing Crescent Sets?

The Moon, like the Sun, rises from the East and sets after about 12 hours at the west (with exceptions at high-latitude areas), and since the waxing crescent lies near the Sun, it will set after the Sunset, and in its best cases, the new waxing crescent sets about one hour after the Sunset.

* Are the 10 hours only, enough as a factor to determine the crescent visibility?

Of course not. There are several factors that must be met in order to view the thin waxing crescent: one of these factors is the crescent's altitude, it must be about 3 degrees or more, and the angular distance between the centers of Sun and Moon must be 5 degrees or more (number of degrees from east to west equals to 180 degrees), and the Moon's staying ( the interval between the Sunset and the Moon set) must be 12 minutes or more. But we must realize that an excess of one of these factors may compensate the lack of another factor, i.e. if the angular distance between the Moon and the Sun is 10 degrees and the Moon's altitude is just two degrees, then the big angular distance may compensate the small Moon's altitude.

* What's the Meaning of Astronomical Calculations of the Crescent?

Most people think that the astronomical calculations mean absolute determination of crescent visibility, but this is not true, the astronomical calculations include the following:

  1. The time of the wane Moon (New Moon) must be determined, and this time is accurately calculated. For sure there is no chance for any error.
  2. The Moon's altitude and the angular distance between the centers of the Sun and the Moon at the Sunset are determined.
  3. Sunset time and the Moon set time are calculated. In addition to the Moon's staying period (period between Sunset and Moon set) as it must be more than about 12 minutes.
  4. The results of the above calculations must be compared with crescent visibility conditions in the previous years, and with the accurate practical and international observations. If you have a report concerning a very young Moon visibility kindly send us your report by E-mail or ordinary mail.
Note: It is absolutely impossible to see the thin waxing crescent after sunset if the Moon didn't reach the Wane phase (New Moon) yet. How can we see the new crescent if it is not wane yet?!. " Who claims that he viewed the thin waxing crescent before the New Moon instant, is like the one who claims that he saw the Sun before dawn, or he saw the baby before delivery", ancients said.

* Conclusion:

To locate the thin waxing crescent, we have to start looking for it after a while of the sunset at the West, a little bit above the point at which the Sun sets, in its best cases, crescent sets about one hour after Sunset. You will find below a table showing the crescents viewing conditions during 1998.

"New MOONS" Not "New MOON" !!

The New Moon phase is defined as the instant at which the apparent celestial longitudes of the Moon and the Sun are the same. Considering the Sun, Moon, and the Earth to be points not disks. Adopting this definition, the New Moon phase is certainly a unique instant all over the world. But in reality the Sun, the Moon, and the Earth are viewed as disks not points, and so, observers on the Earth in different locations will not see the centers of the Sun and the Moon at the same longitude in the same instant. The difference may reach up to four hours. This would be obvious during a solar eclipse, which can be considered as a "visible" New Moon phase, since it is well-known that a solar eclipse does not begin at the same instant all over the world.

For most purposes, it is suitable to consider the New Moon phase as a unique instant all over the world, and so, nearly all the astronomical books and magazines publish times of New Moon phase as a unique instant, which is for the center of the Earth. But to observe the very thin crescent shortly after the New Moon phase, and to know the exact interval between the New Moon phase and the observation time (Moon's age), we should adopt the instant of the New Moon phase that occurs from the location of observation. Consequently, times of the New Moon phase in this document are calculated for Amman, or for Iraq in the Iraqi report.

To calculate the Topocentric new Moon, prayer times, and Qiblah direction, kindly download the program "SalatTimes" by Ali Alhadad.

Comments from Scientists Concerning the above Paragraph

  1. Dr. Myles Standish, president of the Ephemerides Commission / IAU, "I found the explanation of the Moon's phases very well-written and easy to understand. The example using solar eclipses to illustrate why true "New Moon" occurs at different times on the Earth should be very helpful for people."
  2. Mr. Dennis McCarthy, United State Naval Observatory (USNO), "I've looked over the "New MOONS not New MOON" section and it looks good."
  3. Mr. Jean Meeus, A well-known astronomer and mathematician, and author of many astronomical books, which are devoted to astronomical calculations, "Counting the age of the Moon from the topocentric New Moon makes sense for instants shortly (a few hours) after the conjunction.
  4. Dr. Richard Miles, British Astronomical Association (BAA), "My first thoughts are that the text is essentially correct. Many astronomical phenomena are expressed in terms of the geocentric condition, which can never actually be observed as it is impossible to reach that particular observing site (at the centre of the Earth !).
    However the geocentric configuration is a useful one for distant objects but of course the Moon is near.
    Of course the centres of the Earth, Moon and the Sun are rarely in line - this corresponds to a total solar eclipse. At other times, locations away from the line, there is a crescent Moon. Thus even at New Moon from any particular location the crescent will change in extent and position. Likewise when New Moon is defined for a particular observer on the Earth, as the Moon and Sun sharing the same celestial longitude (Right Ascension), the crescent will be positioned either north or south near to but not necessarily centered on the poles of the Moon (libration of the Moon defines the extent to which it appears to wobble). Of course there will be a line roughly in longitude where all observers on the Earth will see the Moon and Sun at the SAME Right Ascension.
  5. Mr. Ali Alhadad, holds Bsc and Msc in the fields of mathematics and Computer logic, "I find your article (Visibility of Crescents) interesting and I have the same opinion regarding the use of Topocentric New Moon instead of the Geocentric one. However, only two comments I have in mind: 1- The difference between Topocentric and Geocentric New Moons can reach up to +-2 hours, 2- The difference between Geocentric Elongation and Topocentric can reach up to 1 degree (These two statements are not in the current version of your paper but still worth to mention)
  6. Mr. Roy Bishop, the editor of the The Observer's HandBook, of the Royal Astronomical Society of Canada (RASC), revised the above paragraph in detail, and made a few corrections.
  7. Prof. Francois-Rene Querci, astrophysicist at Midi-Pyrenees Observatory in Toulouse, revised all this document and made a few corrections.
  8. Dr. Reinhold Bien, and Dr. Ulrich Bastian, Astronomisches Rechen-Institut in Germany, gave some comments. However, they tend to prefer the geocentric configuration than the topocentric.

    Many thanks for those who assist JAS, their efforts are highly appreciated. Furthermore, JAS welcomes any other comments or suggestions.

Visibility of Crescents from Amman, Jordan in 1998

Thu Al-Kea'dah26/0220:4317:3617:26-03:07-1002:05-03:44Impossible28/02
Thu Al-Hejjah28/0304:2117:5818:2713:372907:1604:09Possible29/03
Muharram26/0416:0119:1819:2003:170204:58-01:17Not Possible28/04
Rabeea' Awwal24/0605:2219:5120:0214:291107:4800:24Difficult25/06
Rabeea' Thani23/0718:0319:4519:3501:42-103:31-03:37Impossible25/07
Jamadah Al-Aulah22/0803:3419:1819:3515:441706:1701:39Difficult23/08
Jamadah Al-Aakherah20/0920:5218:4118:44-02:110301:53-01:13Impossible22/09

Remarks Concerning The Table:-

Iraqi Observations for The Crescents

The Space and Astronomy Group, in the Physics department, Baghdad University in Iraq, sent us a report concerning the crescents of the religious months that they saw from 1987 to the beginning of 1997. They hold B.Sc. in Astronomy or Physics, and work at the Iraqi National Astronomical Observatory.

- Location of the Observatory (Place of Observations): Koreok Mountain, Al-Mossul, Northern Iraq.

- Coordinates of the Observatory

- The Instruments:-

Unfortunately these instruments were crashed during the Iraq-Iran War, and during the Second Gulf War ! So the following crescents were seen by small telescopes such as 8 inches.

- Conditions in this place:-

Crescents Seen

Friday23/10/87Rabeea' Awwal1408-00:1210:5920:1912
Thursday14/07/88Thu Al-Hejjah140805:0908:3819:0143
Monday03/07/89Thu Al-Hejjah140903:1205:5713:0733
Saturday23/06/90Thu Al-Hejjah141007:1211:4921:0656
Monday01/06/92Thu Al-Hejjah141202:5906:0513:4432
Wednesday18/08/93Rabeea' Awwal1414-01:1312:4920:2306
Thursday18/04/96Thu Al-Hejjah141604:2207:5917:0436

* Remarks Concerning the Table:-

Our Criteria for Crescents Visibility

The following criteria for crescent visibility are adopted by Prof. Hamid M.K. Al-Naimy, an astronomy Professor at Al al-Bayt University (after two years of observing crescents), and by Mr. Awni Khasawneh, who holds a M.Sc. degree in astronomy from the same University (after studying many sightings of the crescent), and by JAS.

  1. Moon's age is equal to, or more than, 10 hours.
  2. The angular distance between the Sun's center and the Moon's center at Sunset is equal to, or more than, 5 degrees.
  3. The Moon's altitude at Sunset is equal to, or more than, 3 degrees.
  4. The interval between Sunset and Moon set is equal to, or more than, 12 minutes.
If the crescent satisfies these conditions, it is expected to be seen through telescopes from a highly-elevated and clear area. Knowing that an excess of one of these factors may compensate for the lack of another, for instance, if the angular distance between the Moon and the Sun is 10 degrees and the Moon's altitude is just two degrees, then the big angular distance may compensate for the small value of the Moon's altitude.

Methods to Start the Islamic Months in Different Countries

There is not a unique method adopted by all the Islamic countries to start the Islamic months. There are many methods spread all over the Islamic World, some of them are:-

  1. If the Wane Phase (New Moon) occurs before midnight, then the next day is the first day of the Islamic Month. This method is adopted in astronomical books and magazines and some Islamic countries.
  2. If the Wane Phase (New Moon) occurs before Sunset, then the next day is the first day of the month. Since the Islamic day starts at Sunset not at midnight.
  3. Some countries adopt specific criteria, such as the Moon's age, altitude, the interval between Sunset and Moon set,...etc., and if the Moon fulfills these criteria at Sunset, then the following day is the first day of the Islamic Month.
  4. Some countries adopt the actual sighting of the crescent with the assistance of astronomical calculations. This is the most reliable and accepted method among people and scientists, as well as among most of scientists of Islamic Shari'a nowadays. JAS adopts this method, since the Prophet Mohammad "ASWS" ordered us not to start the month except when we view the crescent, thus it must be seen, and we use astronomical calculations in order to know where and when to observe, as well as the probability of observing the crescent, since sometimes it would be useless to observe the crescent if the calculations show that there is no crescent after Sunset !
  5. Other countries adopt several different ways, some of them make the month 29 and 30 days alternately, others make Ramadan either 29 or 30 days always, and finally some countries don't adopt any specific thing !

The Actual Saudi Date System

Most people think that Saudi Arabia always adopt the actual sighting of the crescent as the basis to start Islamic months. But during the previous years, it was very clear to the public as well as to astronomers that most of the Saudi months were wrong if the actual sighting is the basis for starting the Islamic month. Fortunately, JAS received a telegram from The Highest Religious Council "Majlis al-Ifta' al-A'ala" in Saudi Arabia confirming that Saudi Arabia adopts the astronomical calculations and totally ignores the actual sighting. Below is a literal translation of this telegram.

"( To Jordan/ Al-Yadodeh/ M.Kh./ Al-Sook/ Mr. Hayel Mamdooh Abu-Zeid, dated January 21, 1998/Ramadan 23, 1418H.

We wish to thank you for sending us your greetings of Ramadan, and for reminding us of the date of the New Moon of Shawwal for the year 1418 H. We would like to remind you that determining the first day of the Islamic month is like determining the prayer times, and the aim of His Almighty from these times is to inform us not to take it as worship. It is adopted in Umm-ul-Qura Calendar that if the Moon's age at Sunset is 12 hours or more after the New Moon then the PREVIOUS day is the first day of the Islamic month, since the Islamic day starts at Sunset, and the night is before the daylight, as well as the time of fasting is in the civil daylight. May Allah accept your worship. May Allah bless this Ramadan. Thanking you for your good cooperation.

From: Kingdom of Saudi Arabia/ Al-Riyadh/ The Higher Religious Council "Majlis al-Ifta' al-A'ala"/ Mohammad Bin Ehmead.)"

Mr. Hayel of JAS received other letters also, about the same subject, which were clearer than this telegram. The following example may make their system clearer: If for example 29th Dec is 29 Sha'ban, and the New Moon Phase occurs after Sunset in Riyadh, say at 11 pm on 29th Dec., then the next day (30th Dec.) at the Sunset (For example at 5 pm) the Moon's age will be 18 hours which is more than 12 hours, so that day (30th Dec.) is the first day of Ramadan, even though the New Moon was not even born at the Sunset on 29 Sha'ban (29th Dec.), and generally in such cases the Moon will set before Sunset!! Below is a copy of the telegram.

Moon 2.2 (By Moh'd Odeh)

To calculate Moon's Phases kindly Download Moon 2.2. " The program and text are interesting, and a spot check of one year's lunar phases certainly appears to show that the results are quite accurate.", Mr. Roger Sinnott, Associate Editor in Sky&Telescope Magazine.

JAS Observes the Crescents

Looking at the West
Just Before Sunset

The Moon Today 
(Updated every 4 Hours)
Moon's Phase
Moon Sighting Info.
Moon calculator

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By Moh'd Odeh. Jordanian Astronomical Society (JAS), All Rights Reserved. This material may not be reproduced in any form without permission. For more information Send E-mail or contact us at : The Jordanian Astronomical Society (JAS), P.O.Box 35022, Amman 11180 Jordan

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