The beginning of Ramadan is based upon the Islamic calendar and observing the first waxing crescent moon.
Hilal (The Crescent) is typically a day (or more) after the Astronomical New Moon (No Moon). So, since there is only one new moon a month, Muslims can safely estimate the beginning of Ramadan.
Ramadan is a time of reflecting and worshipping God. Muslims are expected to put more effort into following the teachings of Islam and to avoid obscene and irreligious sights and sounds. Sexual thoughts and activities during fasting hours are also forbidden.[Qur'an 2:187] Purity of both thoughts and actions is important. The fast is intended to be an exacting act of deep personal worship in which Muslims seek a raised awareness of closeness to God.
Ramadan is also a time when Muslims are to slow down from worldly affairs and focus on self-reformation, spiritual cleansing and enlightenment, establishing a link between themselves and God through prayer, supplication, charity, good deeds, kindness and helping others. Since it is a festival of giving and sharing, Muslims prepare special foods and buy gifts for their family and friends and for giving to the poor and needy who cannot afford it; this can involve buying new clothes, shoes and other items of need. There is also a social aspect involved the preparing of special foods and inviting people for the Iftar meal (the meal to open the fast).