Masterpieces of astronomy for over 1000 years

April 4, 2016 OPINION/NEWS


Narges Kharghani


The most accurate calendar in the world 


The Iranian astronomy calendar is the most accurate and most complete calendar in world. The calendar was written according to the Earth’s motion around the sun. For example, compared to the a.d. calendar which has an error of one day every 3320 years, the Iranian calendar has just a second error every 10,000 years!

For this reason many mathematicians and astronomers believe the Iranian calendar is the most complete calendar in the world. This calenda also has a very interesting story…….


Reasons for the emergence of the Iranian calendar


Iranians wrote their first calendar 7000 years ago, and in this calendar March 21 was the first day in the year and this day was the first day in the spring season. Nobody knows who wrote this calendar, but it changed many times before finally being converted. This calendar is famously known as the solar calendar in Iran.

In 1006 there was a king in Iran named Jalalodole Malek Shah Saljooghi. This was 400 years after the Arab invasion of Iran at which time Iranian people didn’t have ancient religions (1). They were Muslim and had to use the Arabic calendar (2). This has been removed by many sources regarding the calculation of the Iranian calendar, so determining the first day of the year brought numerous mistakes.

Jalalodole Malek Shah Saljooghi ordered the Iranian calendar’s recomputation and to be re-written, because Iranian people had problems calculating important holidays in Iran such as Nowruz and Yalda (4).

For this purpose the King invited a number of mathematicians and astronomers. Inbetween Omar Khayyam (3) was the best and brightest person, as he was a poet, philosopher, mathematician and astronomer, in addition to being skilled in various fields of science.

The Iranian calendar was first named ‘Jalali’, because this calendar was written under the order of Jalalodole Malek Shah Saljooghi. Without a doubt the Iranian calendar is the best calendar that had been written. This calendar was written following a great deal of research and many observations in Isfahan and Neyshaboor observatory, important cities in Iran at that time.

After the Mongolian invasion of Iran 200 years after Jalalodole Malek Shah Saljooghi, the Jalali calendar was used less, more using the Arabic calendar. But in 1925, the Iranian Parliament approved the Jalali calendar for the domestic calendar in the country. In that year this calendar was named the ‘solar calendar’. Iranians called this calendar ‘solar’ and Arabic people ‘Jalali’, other countries calling it the ‘Iranian calendar’.





1- Iranian people were Zoroastrians before the Arab invasion of Iran. Historical evidence shows more than 90 percent of Iran was Zoroastrian 1400 years ago. This religion from the Old Iranian prophet Zoroaster. He was born in Iran 3000 years ago. At the moment few Zoroastrians live in Iran and India.

2- The Arabic calendar or lunar calendar is used in Arabic countries. This calendar is calculated according to the orbit of the moon around the earth. For this reason this calendar is often 10 days less, more than the solar and a.d. calendar. The Arabic calendar has just 355 days in a year!

3- Omar Khayyam is an Iranian poet, philosopher, mathematician and astronomy. He had contributions in different sciences. He was the first person who proved third degree equations may have more than one answer or there may be questions. Khayyam did many works in algebra that they use to this day. Theories of materialism in philosophy were very controversial 1000 years ago. Khayyam stated his philosophy theories in his poems. There are many opinions about Khayyam’s poems still. Western nations recognized the philosophy of Khayyam for the first time by Edward FitzGerald’s translation of Omar Khayyam’s poems. Edward FitzGerald was an English writer in the 19th century. For a while he lived in India and read Khayyam’s poems, loving his philosophy also. In western countries Khayyam is known as a famous philosopher, his other aspects being relatively unknown..

4- Yalda is the longest night in the year, this night being very important in Iranian ceremonies. It is held every year on 21 December. On this night Iranian people have parties and family members gather and sing poems, eating fruits such as watermelon and pomegranate with nuts, and don’t sleep until the close of morning.



The Persian calendar’s features


The Persian calendar is a fusion of Islamic and Iranian beliefs beside accurate calculations about mathematics and astronomy. The first year of this calendar is similar to the Arabic or lunar calendar and its synchronous to the date of the immigration of the Prophet of Islam from Mecca to Medina (1).

But the first day in the Iranian calendar is the first day of the Nowruz (2) ceremony and this relates to the beliefs in Iran’s ancient history. Iranian people have been holding this ceremony for more than 7000 years. The first day in the Iranian calendar is March 21. This day is the first day of spring in astronomy. March 21 is also the first day of the Nowruz ceremony also. The Nowruz ceremony is an important celebration for Iranian people, held to celebrate the New Year. The importance of this occasion for Iranians is much similar to the importance of Christmas for Christians.

But on the other hand, another important thing in the Iranian calendar is the first day of summer which is synchronous to June 22. In astronomers’ eyes, this is the exact day for the first day of summer in the northern hemisphere, people experiencing the longest day of the year in the northern hemisphere on this date.

In Ithe ranian calendar, the first day of fall is September 23. It’s interesting that this change in the calendar is very deliberate and occurs carefully in the Iranian calendar, fall beginning exactly this day in the northern hemisphere, the radiation becoming very diagonal in that time of the year.

The first day of winter in the Persian calendar is December 22. The night before that day, December 21 is named Yalda night in the Iranian calendar. Yalda is a very important ceremony for Iranian people and is similar to Nowruz and has been held for more than 7000 years. The Iranians believe that Yalda is the longest night of the year and because of this, Iranians have been celebrating this day for a great number of years. Another reason is that the day following Yalda night, days become much more longer and people celebrate the victory of the light over darkness.

One of the other interesting things about this calendar is based on detailed astronomic calculations, people experiencing the longest night in the northern hemisphere on December 21. On this night, in many areas near the North Pole, the sun does not rise.

Another amazing point in the Iranian calendar is that the number of days per season is very regular and accurate. For example spring is 93 days in 3 months, summer is 93 days in 3 months, fall is 90 days in 3 months and winter is 89 days and a few hours and a few seconds in 3 months.

Winter sometimes becomes 90 days and this rare occasion happens every 4 years. This year is called the Kabiseh in the Iranian calendar, unlike the a.d. calendar in which the year starts at midnight.

But in the Iranian calendar, the time of the beginning of the year changes every year, according to some astronomical calculation. Even seconds are considered in this calendar and for this reason, astronomers name the Iranian calendar as a great masterpiece of calculation which has only a few mistakes every 10,000 years.

The names of Persian months in the Iranian calendar are retrieved from the name of Iranian months just before the deployment of Islam, and in fact in this calendar original Iranian names are used. At the end of this article you can see the name, the first day and the number of these days in the Iranian calendar, per months in this table:




The name of the month

Number of days in each month

The first day of this month




March 21



April 21



May 22




Jun 22



July 22



August 23




September 23



October 23



November 22




December 22



January 21


29 days- every 4 years becomes 30 days

February 20




1- Muhammad the Prophet of Islam was born in Mecca and became a Prophet at 40 years old. But a few years later in 622, he was forced to emigrate from Mecca to Medina, another important strategic city in Saudi Arabia. After this immigration, those who accepted Islam experienced significant developments about their beliefs and that’s why this time has been chosen for starting the history of Islam and starting the Arabic calendar. In the Iranian calendar the starting point is at 622 ad.

2- The Nowruz ceremony coincides with New Year in Iran. It has been a few years since Nowruz was recognized by the United Nations as an ancient international ceremony, because it is not just an important occasion in Iran, it has been held in other countries too, such as Afghanistan, Tajikistan, Uzbekistan, Turkmenistan, Kazakhstan, Kyrgyzstan, Azerbaijan and parts of Kurdish areas in turkey, Iraq and Syria. So we can name the Nowruz celebration as the most important ancient festival all around the eastern areas of the world.








Narges Kharghani






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