Happy Eids

Once again Eid-ul-Fitr was celebrated on two days in the UK. The problem is related to the fact that the Muslim calendar begins with the first sighting of the sliver-thin, crescent moon. In this age of science, it is indeed embarrassing that we are unable to decide on a single day for Eid. Why, we can ask, can we not rely on visibility calculations, which have now achieved a level of accuracy not known in earlier centuries? Why must people insist on a literalist interpretation of the sighting of the moon? Using visibility calculations will introduce a degree of certainty. If people are willing to base prayer times and times for breaking the fast on precise timing (e.g. 8:07pm for the last day this year), why are people not willing to base the decision to start fasting and to celebrate Eid on calculated times?