Question: Why do we have to sight the moon for starting Ramadan? Why is the lunar calendar followed in Islamic rituals? Is there any advantage in following this calendar? Also, why is it that Eid happens one day after it is celebrated in Makkah? 
    Answer: Eid al-Fitr is observed at a particular day of the Islamic Calendar, which is based on the movements of the moon. According to this calendar, the beginning of each month is marked by the appearance of the moon above the horizon. This appearance can be observed by the naked eye. If accurate mathematical calculations can help in this sighting, physically observation is not required. Consequently, just as clocks have helped man in accurately determining the time of the five prayers and one no longer needs to measure one’s shadow for this, if at some point of time (if not already) scientific advancement is able to determine the exact time of the appearance of the moon, then, on similar grounds, one can benefit from this. 
    The lunar calendar was followed by the Arabs more out of necessity than choice. In the absence of clocks, the easiest way to measure time was through stars and the moon. The Arabs like their contemporary nations were well versed in finding out time through the passage of the heavenly bodies. Moreover, since the lunar calendar falls on different dates of the solar calendar, the lunar months fall in different weathers each year making the inhabitants of the earth experience Eid and other religious rituals (like Hajj) in different seasons. This of course is a great advantage.
    Because Eid is dependent on moon sighting, which is at different dates in different areas, Eid day at Makkah and other places is likely to be different.