☰ Contents · Astronomy

The Moon, calendars and eclipses

Lessons 15–17 · 3 lessons · M. Mamadazimov. Astronomy Grade 11, 1st edition. DAVR NASHRIYOTI, Tashkent, 2018
16

The lunar and solar Hijri calendars

Textbook: pp. 27–28
GoalDescribe the structure of the lunar and solar Hijri calendars and calculate their lengths and the difference in days.
New words
Hijri calendar · hijriy kalendarMuharram · Muharramlunar calendar · oy kalendariJalali · Jaloliy
Explanation

The Hijri lunar calendar began in 622 CE (1 Muharram, ≈ 16 July in the Julian calendar) and is a purely lunar calendar: 12 months of 29 or 30 days, a year of 354 or 355 days. It is ≈ 11 days shorter than the solar year, so its months drift through the seasons and in about 33 years it gains a whole year. The start of a month is set by sighting the crescent or by calculation (a table): in a 30-year cycle 11 years are long. The solar Hijri calendar (used today in Iran and Afghanistan) starts at Navruz, the vernal equinox, and follows the seasons; its epoch is also 622, and its structure goes back to the 11th-century Jalali calendar. Ulugh Beg’s zij contains conversions between calendars (Hijri, Chinese-Uyghur and others). The present (late 2026) Hijri year is 1448, which began in June 2026.

Worked examples
12 months: 6 · 30 + 6 · 29 = 354 days; the difference from a 365-day solar year is 365 – 354 = 11 days.
In 33 years the difference is 33 · 11 = 363 days, almost a whole year: 33 lunar years ≈ 32 solar years.
Class activity

Find an online Hijri–Gregorian date converter, find the Hijri date of your birthday and tabulate for 5 years how the date of Muharram shifts in the Gregorian calendar.

Practice
1
How many days can a lunar Hijri year have?
2
By about how many days is a lunar year of 354 days shorter than a 365-day solar year?
3
Why does a month of the lunar Hijri calendar fall in a different season each year? (From the calendar point of view only.)
4
How does the solar Hijri (Jalali-based) calendar differ from a lunar calendar?