When do we start observe Saum?     Fasting the month of Ramadan is based on observing the cresent of the month of Ramadan, not based on calculated Calender as some Muslims do. Prophet, peace be upon him, said: "When you see the cresent (of the month of Ramadan) observe Saum (fast), and when you see the cresent (of the month of Shawal), stop observing Saum; and if the sky is overcast (and you can’t see it) then regard the cresent (month) of Rqamadan (as of 30 days)." (Al-bukhari)     The best way is to follow Allah’s Apostle, peace be upon him, and fast base on observing of the moon. And if the sky is not clear due to dust or cloud, we should complete the month of Sha’aban or the month of fasting 30 days.