In the Name of Allah, The Most Gracious, Ever Merciful.
Love for All, Hatred for None.
The visibility of the crescent is not a function of the age of the moon
(time elapsed since conjunction, or “astronomical new moon”). The
visibility of the new moon is a function primarily of the angle between
the moon, observer, and sun (which affects the brightness of the crescent)
and the apparent altitude of the moon above the horizon and of the sun
below the horizon (which affects the background brightness against which
the moon is to be observed). Of course, as the moon “grows older” these
angles do increase, so the more time that elapses, the more likely it is
to see the moon. But one cannot ignore the actual position of the moon in
the sky. Thus, it does not automatically follow that if new moon (conjunction) occurs on one day the following evening (or even necessarily the one after that! ) the moon would be visible.
Many Muslim communities make a calendar predicting the dates of Ramadan based upon scientific predictions of when the moon should be visible. The actual start and end of the month of Ramadan is (just like every other month on the Islamic calendar) based upon the sighting of the moon. Do not confuse the Islamic new moon, which is when the moon is first visible, to the astronomical new moon. The astronomical new moon, as listed on newspapers and most astronomical sites (such as the US Naval Observatory site), is when conjunction occurs, and the moon is dark; the age of the moon starts from this point. The Islamic new moon is when that first little sliver of the moon (the crescent or hilal) is first visible. That night starts a new month, and the following day would be considered the first day of the new Islamic month.) There are many conditions for the sighting of the moon in any location. However, as time has progressed and technology has advanced, the ability to predict the sighting of the moon has increased.
Without getting into the debate as to which set of criteria to use, a consensus seems to be growing towards using the method developed by astronomer B. D. Yallop. In Britain, H.M. Nautical Almanac Office has adopted this formula for determining the visibility of the moon. This formula results in a visibility parameter given in a range of A to F. The range of the parameter corresponds to the following visibility types for the new crescent moon:
(A) easily visible to the unaided eye
(B) visible under perfect atmospheric conditions
(C) may need optical aid to find the thin crescent moon before it can be seen with the unaided eye
(D) can only be seen with binoculars or a telescope
(E) below the normal limit for detection with a telescope
(F) not visible, below the theoretical limit
(see “NAO Technical Note No. 69 - A Method for Predicting the First Sighting of the New Crescent Moon by BD Yallop”).
The old style is preferred by many, though, and common sense seems to dictate that if one actually sees the moon with one’s eyes, then an ounce of observation is worth a ton of calculation! Of course, you have to be careful that people will often make an honest mistake in seeing things that aren’t there. (There was an experiment where astronomers took people out in the field and told them to look for a particular very faint star. About 15-20% of the people saw the star. However, it was really a trick. There was no star! It may be somewhat analogous to the placebo effect in medicine.)
With all of these factors taken into consideration, most Muslim communities make a calendar predicting the dates of Ramadan. Since sunrise and sunset can be calculated with accuracy, along with precise positions of other planets, comets and other heavenly bodies, it should be no shock t hat science has progressed to where we can predict when the moon should first be visible also. Given the visibility parameter published by H.M. Nautical Almanac Office, visibility types A, B, and C correspond well with the Muslim concept of being able to sight the moon by eye for the commencement of the Islamic month. This parameter can be obtained through the use of the Websurf service of H.M. Nautical Almanac Office.
Therefore, although many believe that you should only make official the start of Ramadan after actually seeing the moon, the use of these proven scientific calculations from the latest, state of the art tools, coincides with the actual observations we have made in the sky. This may be just one more example of how there is no clash between traditional Islamic principles and the modern age, they can be in complete agreement; and the traditions of Islam are just as relevant and valid today as they have been for centuries.