The purely lunar year of the Islamic Hijri calendar can have 354 or 355 days, (i.e., in a 30-year cycle, 11 years have 355 days and the rest 354 days). Accordingly, the lunar year is shorter than the Christian Gregorian solar year by about 11 days. Consequently the Islamic events and festivals gracefully pass through all four seasons.

It is interesting to note that the birthday of the Holy prophet (12^th Rabi-ul-Awwal) occurs generally 71 days after the commencement of the Hijri year (1^st of Muharram). The first of Ramadan occurs one hundred and sixty-six days after the holy Prophet's birthday. Ramadan as well as other months sometimes have 29 and sometimes 30 days. Then the Eid-al-Adha (10 Dhul-Hijjah) generally falls 98 days after the 1^st of Ramadan. There may be the variance of one day between the dates given in this Schedule of Events and the actual sighting (NOT the invisible birth of the astronomical New Moon)of the Crescent in a particular horizon, which alone determines the feasts, festivals and Eids for the people of the locality. Muslims should also realize that a Crescent following a month of 30 days, will look larger and stay longer than the Crescent following a month of 29 days.

Many people think that Saudi Arabia adopts the actual sighting of the crescent as the basis to start Islamic months. But during the previous years, it has been very clear to the public as well as to astronomers that most of the Saudi months were wrong if the actual sighting is the basis for starting the Islamic month. A Muslim organization on the Internet (The Jordanian Astronomical Society) received a telegram from The Highest Religious Council "Majlis al-Ifta' al-A'ala" in Saudi Arabia confirming that Saudi Arabia adopts the astronomical calculations and totally ignores the actual sighting. The actual telegram may be viewed here.