Sheik Nasirudin Albanee (RAH) on crescent based on astronomical calculation

Extracts from the Book Fataawaa of Shaikh Al-Albaanee (rahimahullaah)
From Al-Asaalah Magazine Issues 1-21
Translated and Arranged by: Isma'eel Alarcon

"In some of the western lands, such as America, there were some Islaamic Callers (i.e. people of Da'wah) who announced that their method for confirming the crescent at the beginning and end of the month was based on astronomy.

Either they were ignorant of the truth or they disregarded it and pretended to be ignorant about it. And as it is said: "The sweeter of the two is (still) bitter."

The Prophet, sallAllaahu 'alayhi wa sallam, said: "We are an illiterate nation. We do not record nor do we estimate. A month is like this, like this and like this – [or he sallAllaahu 'alayhi wa
sallam gestured with his hands three time like this, and this and this, meaning thirty days]."
Then he, sallAllaahu 'alayhi wa sallam, said: "A month is like this, this and this [meaning twenty nine days]."

And in some of the authentic narrations, he, sallAllaahu 'alayhi wa sallam, said: "And if it becomes too cloudy, then complete the month as thirty days." In many of the lands in which the people give rulings according to their own way, some astronomers confirm the crescent for Ramadaan by astronomical estimations and calculations.

And the Messenger, sallAllaahu 'alayhi wa sallam, has nullified this type of means. Even if it is a means based on knowledge, then only a few people in some lands are aware of this knowledge. Whereas the prescribed means that the Messenger, sallAllaahu 'alayhi wa sallam, has made as a proof for the beginning of the new month or the termination of the current month is the innate natural and human means of physical sighting. And it is not the scientific sighting, which we are not able to share knowledge of to all people.

Based on this, it is not permissible to cast off this type of means, which Islaam has brought, by claiming that times have advanced and changed. So it has become clear from by previous explanation that it is not proper today to take a means that the Messenger, sallAllaahu 'alayhi wa sallam, was able to take (during his time, but which he didn't). The discussion on this topic will prolong severely.

Ibn Taimiyyah has a very beneficial section in his book Iqtidaa As-Siraat-il-Mustaqeem Mukhaalafatu Ashaab-il-Jaheem dealing with this matter. I will abridge what I can from the words of Ibn Taimiyyah:

The means that are introduced in a time and a place are divided into two categories:
1. A means of which a need for using it existed during the time of Allaah's Messenger, sallAllaahu 'alayhi wa sallam, but he did not use it. So introducing it is an innovation.
2. A means of which there did not exist a need to use it during the time of Allaah's Messenger,sallAllaahu 'alayhi wa sallam.

He (rahimahullaah) said: "So it should be examined. If the need for introducing this means and using it is to make the Muslims refrain and lessen in their application of the rulings of the Religion, then it is not permissible to use them. And if this is not the case, then it is permissible."
And Allaah is the One who grants success. [Al-Asaalah, Issue#18]