The word 'Ro'ya' as mentioned in ahadith is not limited, in it's meaning, just to visibility and it also refers to 'knowing'. It has been used in the Qur'an many times for this meaning such as Surah al-Fil v. 1 "Have you not seen how your Lord dealt with those who had elephants?"
This refers to an event which took place before the birth of Holy Prophet (peace & blessings be upon him), so this was in knowledge and not visualised.
From the beginning and until recent times, Muslims have used visuals to determine the new moon as there was no other means to certify it. Muslims developed telescopes to help make determinations. This also shows Islam did not oppose this method. In today's day and age, there is no need for visualisation of the moon because of scientific advancement we are able to calculate with certainty the number of hours, minutes and seconds, for the new moon to be born. We have certain knowledge. Whereas there can be errors with regards to witnesses who claim to have seen the moon such as in Nigeria in 2017 which became controversial and unacceptable by groups of Imams.
Although the classical hanafi position requires actual moon-sighting, there is a Shafi' position to accept calculated methods. It is, therefore, a valid shari' opinion. Furthermore, there is no bar upon conducting ijtihad, which is inherently required due to the change of circumstances. It is the same ijtihad which has been unanimously accepted in Sahoor and Iftar calendar times that have been drawn up through astronomical calculation.
If the Muslims agree upon scientific methods then the ummah will be united on the day of Eid al-Fitr every time as it will be known well in advance.
