On March 20, Iranians rang in the year 1404 of the Persian
calendar, marking the astronomical moment of the spring equinox. Around the
world, an estimated 300 million people will wish one another a happy new year—Norouz mobarak in Persian—not just
in Iran but also in Afghanistan, Kazakhstan, and among Kurdish communities in
Turkey and Iraq.
The Persian calendar, which has Zoroastrian roots, begins
with the Hijrah—the Prophet Muhammad’s migration from Mecca to Medina—in 622
A.D. Officially adopted in Iran in 1925, this calendar alternates between
common and leap years.
While the Gregorian calendar is the most widely used system
today—especially in Western countries—dozens of other calendars remain in use
across the globe, shaped by religious traditions and regional histories.
Solar calendars
Like the Persian calendar, the Julian and Gregorian
calendars are based on the solar cycle. The Julian calendar, introduced by
Julius Caesar in the first century B.C., aimed to match the Earth’s orbit
around the sun with a 365-day year. It added a leap day every four years to account for the actual solar year of roughly 365.2422 days.
However, the Julian calendar’s slight inaccuracy led to a cumulative shift of about 10 days by the end of the 16th century, disrupting the timing of religious holidays like Easter. To fix this, Pope Gregory XIII eliminated 10 days from the calendar in 1582, jumping directly from Oct. 4 to Oct. 15—thus creating the Gregorian calendar we use today.
Still, some Orthodox churches, such as those in Russia and
Jerusalem, continue to follow the Julian calendar. In May 2023, the Council of
Bishops of the Orthodox Church of Ukraine voted to adopt a revised Gregorian
liturgical calendar—signaling further separation from the Moscow Patriarchate,
which it split from in 2018.
Interestingly, these calendars have no official “year
zero”; they shift directly from 1 B.C. to A.D. 1, based on the estimated birth
year of Christ, as calculated by the 6th-century monk Dionysius Exiguus,
according to retired educator Jacques Gispert in an interview with France
Culture.
Other solar calendars include the Coptic calendar—dating
back to the rise of Emperor Diocletian in 284 A.D.—which influenced the
Ethiopian calendar. The Tamil calendar, now in its year 5125, also follows
solar rhythms.
Lunar calendars
The Islamic, or Hijri, calendar also begins with the Hijra.
Based on lunar cycles, its 12 months contain either 29 or 30 days, producing
years of 354 or 355 days. The start of each month is determined by the
naked-eye sighting of the new moon, which can vary by country.
Because of this variability, the Hijri calendar is not used
for official civil purposes, though it remains vital for determining the timing
of Muslim holidays—explaining why Ramadan shifts about 11 days earlier each
year. According to this calendar, the year 2025 in the Gregorian system corresponds
to 1446.
Lunisolar calendars
Many calendars blend both solar and lunar cycles. The
Hebrew calendar, for instance, aligns its months with the lunar cycle while
maintaining the 12-month solar year.
Each month contains 29 days, and to realign with the solar
year, an extra “intercalary” month is added seven times every 19 years. The
calendar begins in 3761 B.C., the traditional Jewish date of creation. By that
count, the year 2025 corresponds to 5785.
The Chinese calendar is another lunisolar system. It begins
each year with the new moon and adds a 13th month when necessary to keep pace
with the sun—explaining why the Chinese New Year can fall anywhere between Jan.
21 and Feb. 19.
The Buddhist calendar, used in Southeast Asia, begins with
the death of Buddha, estimated around 543 B.C. In that system, the year 2025
would be 2566.