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The Islamic calendar is variously named Islamic, Muslim, Mohammedan, and so forth. It is one of the world's major calendars, used by hundreds of millions of people. |
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In this section, I outline the general structure of the Islamic calendar and summarize its history. |
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9.3.1.1
Structural Details |
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The Islamic calendar is perhaps the only major calendar in current use that is strictly lunar. For the purposes of religious observation and the regulation of daily affairs, the beginning of each month is determined by the first observation of the lunar crescent in the evening sky. For chronological and astronomical purposes, however, the lengths of the months are fixed by rule, not by observation. The rule-based calendar is the one with which the SCDTL system is concerned. |
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The day begins at sunset. The calendar uses a week of seven days. The names of the days of the week vary with local usage. |
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The structure of the year is relatively simple. Each year consists of 12 months, each of 29 or 30 days as shown in Table 9.13. The alternation of 30- and 29-day months is a common technique for producing an average of 29.5 days per month, which is a short-term approximation to the synodic lunar period of 29.5306 days. |
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The leap year is determined by using a system with historical roots in the lunarsolar calendars of the Middle East. Years are considered to repeat in cycles of 30 years. If the Anno Hegirae year (see section 9.3.1.2), modulo 30, is 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, or 29, the year is a leap year. |
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| Table 9.13 Months in the Islamic calendar. | | Month Number | Number of Days | Month Number | Number of Days |  |
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1 |
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| 30 | 7 | 30 | |
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2 |
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| 29 | 8 | 29 | |
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3 |
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| 30 | 9 | 30 | |
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4 |
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| 29 | 10 | 29 | |
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5 |
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| 30 | 11 | 30 | |
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6 |
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| 29 | 12 | 29, 30 in leap years. |
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