(Afghan refugee Shear Jaan prays after breaking fast on the first day of the Muslim holy month of Ramadan, November 17, 2001 near the Pakistani border town of Chaman. REUTERS/Adrees Latif )

When the Muslim holy month of Ramadan arrives next week, fasting will definitely begin on Friday in Germany, probably the same day in neighboring France and maybe on Saturday across the Channel in Britain.

Even in the same country, some Muslims might begin and end the fast before or after others because they follow different rules or disagree on whether they have spotted the new crescent moon, the official start of the month in Islam’s lunar calendar.

This especially causes problems where Muslim minorities live in societies with many holidays based on the Christian calendar that cannot easily accommodate holy days or months whose exact date is determined at short notice.

Frustrated by this confusion, Muslim leaders across Europe are increasingly turning to modern astronomy to help solve the problem. But theological differences, ethnic divisions and the sheer weight of tradition are still holding up progress.