Before attempting to review the major holidays and festivals celebrated in Iran, it is necessary to explain some features of the various systems of dating in use there. The Gregorian calendar familiar to Westerners and now used in many countries around the world is known in Iran, but it has no offi – cial standing (in fact, at times its use has even been outlawed). Dates from that calendar may be given on newspapers or various documents, especially those involving non-Iranians, but this is purely for ease of reference. Instead, Iranians use two other calendar systems for offi cial purposes: the Islamic lunar calendar ( qamari ) and the Iranian solar calendar ( shamsi ). The lunar calendar was introduced in Iran following the Arab conquest and the spread of Islam. For many centuries it was the only calendar in general use, and it still serves as the only system for dating Islamic religious holidays. It was based on an era ( hejri ) beginning with the year of the Prophet Mohammad’s emigration from Mecca to Medina (the Hegira [ hejrat ] in a.d. 622). The year consists of 12 months, each of which begins with the sighting of a new moon. The Arabic names of the months are used, but most are pronounced somewhat differently in Persian: Moharram, Safar, Rabi‘-ol-Avval (I), Rabi‘-ol-Âkher (II), Jomâdâ-ol-Ulâ (I), Jomâdâ-ol-Âkhereh (II), Rajab, Sha‘ban, Ramazân, Shavvâl, Zu‘l-Qa‘deh, and Zu‘l-Hejjeh (in colloquial Persian, the latter two are often pronounced as Zi-Qa‘deh and Zi‘l-Hejjeh or Zi-Hajjeh). Since a lunar cycle takes just over 29.5 days, and the sighting of a new moon depends greatly on local conditions, it is possible any given month might have 29 or 30 days. As a matter of convenience, printed calendars assume the months will alternate between 30 and 29 days, with the last month having one or the other. This enables one to estimate fairly closely when a holiday or other event should occur, but the dates may be off a bit depending on the actual astronomical observations. Long before the coming of Islam, Iranians used a very sophisticated solar calendar, usually referred to in its classical form as the New Avestan Calendar, that was closely tied to the beliefs and practices of the Zoroastrian religion. The year began at the moment of the vernal (spring) equinox, and consisted of 12 equal months of 30 days. There were no weeks, and each day had its own name. Since the tropical year (the time to complete the cycle from one spring equinox to the next) is actually 365.2422 days, intercalary days were added as needed to make up the difference. Other adjustments were to be made every 120 and 1,440 years in order to keep the calendar in sync with the actual position of the sun. A key difference between the two calendar systems is that dates in the solar system correspond consistently to seasons, while those in the lunar calendar do not. Since the lunar year (354.367 days) is shorter than the solar year, dates gradually cycle backward through the seasons: For example 1 Moharram 1400 fell on November 21, 1979, but now, in 2006/1427, 1 Moharram has moved all the way back to January 31. Even in the Islamic period, variations of the old solar calendar thus continued to be used, especially for fi scal and administrative purposes (since it worked better for assessments tied to the agricultural season). The most technically advanced and widely accepted of these solar calendars was the Jalâli calendar, devised by a committee of celebrated mathematicians and astronomers in 1079. In 1911, during the course of the Iranian Constitutional Revolution, the Majles made a version of this solar calendar the offi cial one. It used the names of the 12 signs of the zodiac for the names of the months, but this was modifi ed by a new law in 1925 that restored the use of the names from the Jalâli calendar. These are still in use today: Farvardin, Ordibehesht, Khordâd, Tir, Mordâd, Shahrivar, Mehr, Âbân, Âzar, Dey, Bahman, and Esfand. The year begins at the exact moment of the vernal equinox. The first 6 months have 31 days, the next 5 months have 30 days, and Esfand may have 29 or 30 days. Like the lunar calendar, this solar calendar uses an era beginning with the Hegira, but the difference in the length of the respective years means that the lunar and solar hejri years do not correspond: for example, the current ( a.d. 2006) qamari year, 1427, is 1384 according to the shamsi calendar. The result of all this is that certain holidays are determined on the basis of the national or solar calendar, while Islamic religious holidays follow the lunar calendar (somewhat like the way Independence Day is a fi xed date in the civil calendar of the United States, but the dates of Easter or Yom Kippur vary according to a different religious calendar). Converting the lunar dates to the equivalent in other calendars also involves a certain amount of imprecision and variation from year to year, but the Iranian solar dates can be given an equivalent date in the Gregorian calendar quite easily. The only complication is that the start of the year on the vernal equinox always corresponds to 1 Farvardin but in the Gregorian calendar may be March 21 or March 20 (in leap years). Thus the Gregorian equivalents given in the following discussion would be advanced one day in leap years (e.g., Islamic Republic Day, 12 Farvardin, usually falls on April 1, the Gregorian date on which the event it commemorates actually occurred, but in 2004, a leap year, it was celebrated on March 31).