Moon Sighting and the Beginning of Ramadân

Abû Hurayrah in narrated that the Prophet or (the narrator may have said) Abûn al-Qâsim' (the Messenger of Allâh ) said,
"Start fasting on seeing the new crescent (of Ramadân) and break fasting (at the end of Ramadân) when you see the crescent (of Shawwâl) and if it is too overcast to be seen, then complete counting the month of Sha bân for thirty days (and fast afterwards)“.
'Abû al-Qâsim means the father of al-Qâsim who was the son of the Prophet . The month of fasting that follows Sha 'bân. The month that follows Ramadân in the lunar year. The maximum number of days for a lunar month (the time elapsing between two successive new moons) is 29.5 or 30 full days, and the minimum is 29 days. Reported by al-Bukhârî, "Book of Fasting", hadîth no. 1909, and Muslim, "Book of Fasting", hadîth no. 1809; the wordings are similar. It was also reported by an-Nasâ'ī, Abû Dâwâd, Imâm Ahmad, Imâm Mâlik and adDâramî. There are still other ahadîth that state the same ruling but using
In another narration of the same hadîth by al-Bukhârî, "... but if it is too overcast to be seen, then estimate the (number of days of Sha bân."

Explanation of the Hadîth

A lunar month' is determined through the movement of the moon, the earth and the sun; their respective relative positions that result from their motion.
The moon rotates in a synchronous motion with the earth, as the latter rotates round its axis and round the sun.
The moon rotates on its axis in about the same time that it revolves, and so almost the same portion of the moon always faces Earth. This rotational period of the moon takes place every lunar month; a cycle, which reflects the lunar day. This day is divided into night and day; each of them lasts for half the period of the lunar month (14.5 to 15 days).
Immediately after the moon completes the waning crescent phase, (the conjunction phases where the moon is aligned with the earth and the sun; i.e. the moon being between the earth and the sun) a new moon starts to be born. As the lunar cycle begins, the moon starts to orbit the earth and the illuminated part of the moon gradually increases until the moon reaches the stage of the waxing crescent, the first quarter, the waxing gibbous, then the full moon; the phase where the earth is between the moon and the sun.
As the
different wording, see for example: al-Bukhârî, Sahih, "Book of Fasting", ahadîth no. 1907; Muslim, Sahîh "Book of Fasting", hadîth no. 1797; Mâlik, Mûwatta', "Book of Fasting”, hadîth no. 557, etc. 'Also known in astronomy as the "Synodic month". 2 It is the time it takes for the moon to complete one full axial rotation.
moon continues revolving round the earth, the illuminated part gradually starts to decrease until it reaches the waning gibbous, the last quarter and finally the waning crescent. The moon then disappears in the waning phase until the new moon is born.
The length of the lunar month varies between 29 days and 5 hours to 29 days and 19 hours; an average of 29.53 days. That is why the lunar month ranges from 29 to 30 days, which coincides with what is mentioned in the hadîth of the Prophet R.
An important factor required for the birth of a new moon is that the sunset on that day should precede the setting of the moon. Moreover, for a new moon to be visible in the horizon, after sunset, the moon has to be out of the glare of the sun light.
The legal lunar month (according to the Islamic calendar) starts when the new moon is seen after sunset and ends when the birth of the new moon of the next month is sighted also after sunset. Thus, the interval between the two moons must be complete days, whether 29 or 30. For many astronomical reasons, a pattern of consecutive shorter months (i.e. 29 days) or complete months (30 days) may occur repeatedly once or twice.
Proper and clear sighting of a new moon after sunset in a certain zone of the globe means the birth of the new moon for all the locations, which share the same time line. Furthermore, it should be sighted more clearly in the areas located at the west of that line all over the earth. As for the places to the east of that line, the new moon will be sighted brighter and bigger the following night.
The hadîth of the Prophet indicates that the sign taken for the beginning of a new lunar month is sighting the crescent after sunset on a clear day, but if it is too overcast to be seen.
then Muslims have one of two choice as indicated by the above-mentioned ahâdîth: 1. "...but if it is too overcast to be seen, then estimate the (number of) days of Sha'bân."
2. "...and if the sky is overcast, then complete the month for thirty nights." Estimation then is to be made by those who have the means to calculate and the technology that enables them to do so. As for those who cannot do so, they can complete Sha bân (thirty days).
Glorified be Allah, the Almighty, who taught the last of His Messengers and Prophets, Muhammad that the lunar month could be 29 or 30 days and that the beginning and the end of the lunar month is to be determined by sighting the crescent after sunset.
It is one of the scientific facts which has been perceived by man only in the last two centuries, and the fact that it was mentioned by the illiterate Prophet who was sent to simple nomads, is clear evidence of the truthfulness of his Message.