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          NEW MOON VISIBILTY          

1.What is an Astronomical New Moon?
2.What is the Lunar Month?How Long is it?
3.Predicting Crescent Visibilty?
4.Naked-eye Records for Crescent Sighting
5.Optical-aids Records for Crescent Sighting

1-What is an Astronomical New Moon?

The Astronomical New Moon occurs at the conjunction(Muhaq in Arabic), is the moment when the moon passes between between the earth and the sun. Notice that if the center of these three bodies fall almost in a line, a solar eclipse will occur;At the moment of the New moon, the moon's dark surface faces the earth making itself completely invisible, hidden by the sun's rays. After it moves out from under the sun's rays it starts to become visible.

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2-What is the Lunar Month?How Long is it?

A lunar month is the interval between two lunar phenomena; Astronomy defines more than one kind of lunar month: Anomalistic, sidereal, draconic,..The one that relates directly to the Moon's phases is the Synodic month with an average length of 29.53058 days from the New moon to the next New moon (this will be the same interval of time as between a Full Moon and the next Full Moon-but not between a first and a last quarter).
The maximum length of the lunar month can reach near 29.8 days and a minimum of 29.3 days. New moons examinations by F.Richard Stephenson(University of Durham) and Bao-Lin Liu(Purple Mountain Observatory, China) of a time span from 1000B.C to 4000A.D. found the longest month to had occurred in 400 B.C(29d 20h 6m) and the shortest in 302 B.C.(29d 6h 26m).

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3-Predicting Crescent Visibilty
The sighting of the crescent was essential to know the begining of the Lunar calendar months,
the problem of predicting crescent visibilty has been around since at least Babylonian times, 
throught hebrew and christian old times, and was widely studied by Muslim scholars between 700 and 
1100 A.D., and by different scholars up to this century.
Criterion/factors  proposed for visibilty:

1- Age of the New Moon at Sunset to be more than a certain number of hours: 10, 16, 20 etc...
    i.e   Age = Sunset - New Moon time

2- Time lag: How many minutes the Moon will stay after Sunset
    i.e. Moonset - Sunset.
    Some people take 15 mins. The Muslim astronomer Omar Khayyam proposed a 48 minutes after Sunset
    while Al-ttusi proposed 40 minutes.
3- The Angular distance between the Moon and the Sun, from Earth's center
    i.e. Angular distance of Moon(Assimat-in Arabic), angles right or left from Sun's disc at sunset
    The French astronomer Andre' Danjon, in the early 1930's, deduced that no illuminated portion of 
    the crescent whatsoever can be seen when the moon is 7 degrees or less from the Sun.
    The Muslim Astronomers' Conference held in Istanboul recommended 8 degrees for certainity .
    Explanation: the Moon's path is elliptic, but assume it about circular with an average month
    length of 29.53 days; so the moon travels 360 deg. in 29.53 x 24 hours ;dividing these numbers
    we get about 1.96 hours/degree, multiply by 8 deg. you get a Moon's Age of 15.75 hours
    which is very close to the 15.4 hours , the second naked-eye record.

4-  Moon's altitude above horizon at Sunset; it has to be 5 degrees or more. In rare case the
    crescent was seen between 2 and 5 degrees.

5- Another totaly different approach was developed by F.Bruin in 1979  based on 76 observations 
   from Athens in which he depended on the brightness of the moon and sky and the phsiology of the 
6- Datelines (like Northwest to Southeast curves) proposed by Mohammad Ilyas from Malaysia and 
   different lines by Bradely Schaefer from Nasa and Bernard Yallop.
   [Sky & Telescope Magazine, April 1989, p.373]

Other approaches include a combination of more than one method of the above, like:

 - Khaled Shawkat approach, a  horizontal parabola having a minimum at 20 hrs sighting limit.
-  Jordanian Astronomical Society 
    Age is 10 hours or more, Altitude and Azimuth.

- South African Astronomical Observatory 
   Altitude and Azimuth of Moon at Sunset.

- World federation for moonsighting 
   Age more than 20 hrs and timelag of 15 minutes after Sunset.   

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4-Naked-eye Records for Crescent Sighting

Mentioned in [Sky & Telescope Magazine]:

* There is a doubted observation of an 14.5-hr old moon by two maids in England in 1916.

  Name of observer Date of Observation Location Age S&T issue
1- Steven N. Shore & 4 students [N. Mexico Institute of Mining & Technology] May 1989 11,000 ft Mount Baldy, New Mexico 14 hr 51m Sep 89, p.23
2- Julius Schmidt Sep 14, 1871 Athens,Greece 15.4 hr Jul 88, p.34
3- Stephan O'Meara [S&T Editor] May 24,1990 Mount Wilson Observatory in California, US 15.53hr (15 hr 32m), 9.1 degrees from Sun Dec 96
4- Drummond Laing & 2 wittnesses [S.African Astronomical Observatory] Dec 12,1985 Sutherland 17hr 19m Jun 91

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5-Optical-aids Records for Crescent Sighting
Mentioned in [Sky & Telescope Magazine]:
Name of observer Date of Observation Location Age S&T issue
1- Mohsen Ghazi Mirsaeed, Iran September 7, 2002 Age: 11 hours and 40 minutes
by a giant 40x150 binoculars at a carefully chosen Mountain site and Moon was 7.5 degrees from Sun.
[ref.: Sky & Telescope Feb.2005]
2- James Stamm Jan 20, 1996 Arizona 12 hr 7m Dec 96
by an 8 inch telescope This was a Ramadhan Hilal and 2 other people also spotted it west of his location in Arizona
at ages 12hr 33min and 12hr 50min. 3-Before that the record belonged to Robert Victor using tripod-mounted 11x80 binoculars in Michigan,US on May 5,1989 at age 13hr 28 m. 4-Also a record of 13hr 47 minutes by binoculars..could not be seen by eye. [S&T Sep 89,p.323] another 15 hr binocular record..could not be seen by eye [S&T Jan 91,p.6] Important observations by the Iraqi astronomers at Al-Mousel are listed at the Jordanian Astronomical society page.

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