Numerous regulations order the timing, as well as the correct religious fasting and behavior in the month of Ramadan.
Thus, an extensive literature has grown up around the determination of the beginning and end of the month of Ramadan and the beginning and end of each day of fasting. The exact determination of prayer times, months, and feast days has driven the sciences of mathematics, astronomy, and geography in particular in the Islamic world since the emergence of Islam.
All Muslim feast days, including Ramadan or the pilgrimage to Mecca (Hajj) are once in summer and then again in winter. What is the reason for this? Solar calendar systems, such as the calendar used in Germany, are aligned according to the course of the sun. The months are fixed in relation to the seasons and a solar year lasts about 365 days. However, since the Islamic calendar is aligned with the moon, the Islamic year lasts only 354 days and 8 hours. The Islamic year is about 10-11 days shorter than the solar year, with its progression adjusted to the length of the seasons. In relation to the solar calendar, the dates of Islamic holidays and months therefore shift by about 10-11 days. The month of Ramadan therefore begins at dawn after the appearance of the new moon. In different religious centers of the Islamic world, scholars calculate the beginning and end of Ramadan respectively. Therefore, according to the geographical position, the beginning and end of Ramadan may differ slightly.