In my opinion, a lot of Muslims believe that the Prophet’s directions were to sight the moon [1] (Quoting a Hadith is controversial to some Muslims - I feel though that my points can be made without the Hadiths) - that explains why they still insist on a moon sighting by at least 2 adult Muslims in the same region / country. In my opinion again, some Muslims, e.g. the Saudi’s, use a pre-calculated Islamic calendar (either adjusted regularly or not) to determine the start of each Islamic month.

I think the base question for which there should be an answer is whether physical sighting the moon is important, i.e. did the Prophet direct Muslims to sight the moon in order to start the Islamic month, or is it permissible to calculate the birth of the new moon and begin the Islamic month from that date.

I believe it is possible to accurately calculate the birth of the new moon, but you will agree that there is no accuracy possible in whether a moon can be sighted or not.

Therefore the base question above.

Some background:

• The original Jewish calendar was primarily lunar, with each month beginning on the new moon, when the first sliver of moon becomes visible after the dark of the moon. In ancient times, the new months used to be determined by observation. (from http://www.jewfaq.org/calendar.htm)
• The correct term for birth of a new moon is called conjunction (astronomical new moon) - this is 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.
• The Islamic concept of sighting the moon is known as Roya't (the sighting).
• At the time of the prophet, the Arabs knew of the solar calendar and the lunar calendar because of the presence of Christians and Jews in Arabia. 

In my reasoning, the Islamic month begins when the new moon is sighted. Lets consider a logical explanation instead of the "I-think-the-Prophet-said-so" argument that I feel is devoid of logic.

I understand that the sighting of the new moon will occur several hours after the conjunction. I still hold the reasoning of Roya't because:

• The moon is a reflector of light and not a source.
  • Therefore at and just before conjunction, the moon is completely dark (due to its astronomical alignment) and cannot be seen.
  • This is why it is not considered a new moon at this time because there is "no moon".
• A new moon or a born moon is the moment after that, when the alignment of the moon, earth and sun, allows the first sliver of light to be reflect off the surface of the moon to the earth.
• Due to proximity of the post-conjunction moon to the setting sun, angle, orbital eccentricities, other earthly factors, like atmospheric interference, it usually takes > 15 hours after conjunction to see the new moon on earth even with a powerful telescope.
  • If one went sufficiently high up above the earth so that the angle of observation was different, it probably is possible to detect the first sliver of light from a new moon shortly after conjunction. But now the question becomes, how high should one go - because if you do go really far above the surface of the earth, you may never see the "no moon" or the black moon!
• Switching gears a bit, we know it takes ~ 8 minutes for sun light to reach earth. This means when we see the sunset, or detect it using electronic equipment, the sun has actually already set 8 minutes earlier! But the calculation of Maghrib time is based precisely on when the sun sets for human observers on earth NOT 8 minutes before. Similarly for calculating the times of other prayers.
• Therefore to the human eye, the new moon is not born until humans can see it or detect it on the earth.