Islamic Calendar, which is purely lunar and cycles through the seasons every 32 or 33 years, a convenient provision when fasting is required during the daylight hours in the month of Ramad.an -- neither Northern nor Southern hemispheres are stuck with Ramad.an at times of either long or short days. Curiously, the 30 year cycle of the Islamic calendar commensurates with the 19 year cycle of the Jewish calendar after 1368 solar or 1410 lunar Islamic years. This puts the Islamic Era in 622 at one full cycle after the beginning of the Era of Nabonassar in 747 BC. Another full cycle comes down to our time, in 1990. Anyone disposed to numerological portents are welcome to make of this what they will.THE RIGHTLYGUIDED CALIPHS'Abu Bakr632-634assumes title Khalifah,"successor," to the Prophet'Umar634-644Roman Emperor Heracliusdefeated at Yarmuk, 636; fall of Gaza, Antioch, Mesopotamia conquered from Persians, 637; Jerusalem surrendered, 638; Egypt invaded, 639; fall of Caesarea in Palestine, 640; Persians defeated, 642'Utman644-656attacks in India, 644; Roman army destroyed in North Africa, but army withdraws, 647; Persia overrun, by 651'Ali656-661With the death of the Prophet, some Arabs thought that the House of Islam had ended. They were soon persuaded of the error of their ways, and the armies of united Arabia were turned on Romania and Persia, which were both exhausted from the longest and harshest war they had ever fought against each other. The Roman position in Syria and Egypt was also compromised by the Monophysite heresy of the locals, and its suppression by Imperial authorities. The tolerance of the Arabs for any "People of the Book" seemed preferable, especially after the respect and consideration shown by the Caliph 'Umar when he entered Jersualem. The period of the "Rightly Guided Caliphs," who were all either fathers-in-law or sons-in-law of Muh.ammad, however, ended in some confusion. The murder of 'Uthman was blamed by his powerful Meccan relatives on 'Ali, who was unable to exert authority against them over all Islamic territories. The "bloody shirt of 'Uthman" was thereafter considered a largely cynical ploy by the Omayyads to further their own cause, which soon did triumph at the death of 'Ali, whose sons were either bought off (H.asan) or killed (H.usayn).Although the Omayyads were cousins of Muh.ammad, they definitely had the greater status at Mecca and were originally quite hostile (except for 'Uthman) to Islam. The symbolic crowns in the diagram are for the Prophet and the Caliphs (Khalifah, "successor"). Only that for the Prophet is given with a nimbus, since for the Orthodox only he was divinely inspired and authoritative. The light blue nimbus for 'Ali indicates the Shi'ite belief that he and his descendants were divinely inspired and authoritative also (the Imams). Modern families that trace descent to the Prophet or his family, like Kings of Hijaz, Iraq, and Jordan, call themselves Hashemites.THE SHI'ITE IMAMS1'Ali632-661First Cousin & Son-In-Lawof the Prophet& Fourth Rightly Guided Caliph2H.asan661-6693H.usayn669-680Martyred at Karbala', 6804'Ali Zayn al-'Abidin680-7125Muh.ammad al-Baqir712-7316Ja'far al-S.adiq731-7657Isma'il765-760Schism -- followers of Isma'ilbecome the "Seveners" or"Ismailis," basis of Shi'ismof the Fatimids, the Assassins,and in India7Musa al-Kaz.im765-7998'Ali al-Rid.a799-8189Muh.ammad al-Jawad818-83510'Ali al-Hadi835-86811al-H.asan al-'Askari868-87412Muh.ammadal-Muntazar al-Mahdi874-878Disappears, 878