Most scholars state that scientific calculations can be used to determine if there is visibility of the crescent, but actual sighting of the moon must occur because that’s their understanding of our hadiths. The hadiths seem to indicate the the moon must be visible to the naked eye (or visible in a area that shares the same horizon for example).
I recommend seeing the following videos for a better understanding of that:
https://youtu.be/EUCZdHZjjZs
https://youtu.be/ohpzeUf9w9c