Iranian calendars in the context of "Meridian (geography)"

The Babylonian calendar was a lunisolar calendar used in Mesopotamia from around the 2nd millennium BC until the Seleucid Era (294 BC), and it was specifically used in Babylon from the Old Babylonian Period (1780s BC) until the Seleucid Era.

In the Seleucid Era it was reformed as "Greek time", Anno Graecorum was introduced and used in the Middle East and Egypt until the middle of the first millennium when the First Council of Nicaea AD 325 defined the Church year based on the Roman early Julian calendar. As Anno Graecorum formed the basis for time references in the Bible and spread westward, it rather increased the Babylonian calendars importance. The Babylonian calendar is also partly reflected in calendars in South and East Asia and the Islamic calendar as well as Iranian calendars. The Julian calendar inherited the definitions of the 12 month system, week, hour etc. from the Babylonian calendar and the current Jewish calendar can be seen as a slightly modified Babylonian calendar that still exists today and is practised, but with Anno Mundi Livryat haOlam year calculation since the creation of the world. Today's global time system UTC (Gregorian calendar) therefore has its main structure inherited from the Babylonian calendar.

Nowruz (Persian: نوروز, Iranian Persian: [noːˈɾuːz], lit. 'New Day') is the Iranian or Persian New Year. Historically, it has been observed by Iranian peoples, but is now celebrated by many ethnicities worldwide. It is a festival based on the Northern Hemisphere spring equinox, which marks the first day of a new year on the Iranian calendars and the currently used Hijri calendar; it usually coincides with a date between 19 March and 22 March on the Gregorian calendar.

The roots of Nowruz lie in Zoroastrianism, and it has been celebrated by many peoples across West Asia, Central Asia, the Caucasus and the Black Sea Basin, the Balkans, and South Asia for over 3,000 years. In the modern era, while it is observed as a secular holiday by most celebrants, Nowruz remains a holy day for Zoroastrians, Baháʼís, and Ismaʿili Shia Muslims.

The administrative divisions of Iran are arranged in four levels, the first level of which is the province (Persian: استان‌: ostān). Provinces are divided into counties (شهرستان: shahrestān); counties are divided into districts (بخش: bakhsh); and districts are divided into rural districts (دهستان: dehestān) and cities (شهر: shahr). Rural districts contain villages and other population points. One of the cities of the county is appointed as the capital (مرکز: markaz, or center) of the county.

According to the Statistical Center of Iran, the figures are as follows, as of March 2016 (end of Iranian calendar 1394):

The Solar Hijri calendar is the official calendar of Iran. It is a solar calendar, based on the Earth's orbit around the Sun. Each year begins on the day of the March equinox and has years of 365 or 366 days. It is sometimes also called the Shamsi calendar, Khorshidi calendar or Persian calendar and the most recent of the Iranian calendars. It is abbreviated as SH, HS, AP, or, sometimes as AHSh, while the lunar Hijri calendar (commonly known in the West as the 'Islamic calendar') is usually abbreviated as AH.

The epoch (very first day) of the Solar Hijri calendar was the day of the spring equinox, March 19, 622 CE. The calendar is a "Hijri calendar" because that was the year that Mohammed is believed to have left from Mecca to Medina, which event is referred to as the Hijrah.