Zoroastrian Calendar - The Shahanshahi Calendar

The Shahanshahi Calendar

A 365-day calendar drifts ahead of the solar year at a rate of approximately one day every four years. A ninth century Zoroastrian text, the Denkard, explicitly acknowledged several methods of compensating for this drift:

• a leap-day every fourth year;
• adding ten days every fortieth year;
• a leap-month of 30 days once every 120 years;
• 5 months once every 600 years;
• the discrepnancy would be a whole year once every 1,440 years.

The Denkard then states:

The time of six hours should be kept apart from (i.e. not to be added to) the last days of the year for many years, till (the hours) amount to (a definite period of time)... And it is the admonition of the good faith that the rectification (of the calendar) should not be made till a month is completed (i.e. till the additional six hours every year amount to a month at the end of a hundred and twenty. years). And more than a period of five months should not be allowed (to accumulate.)

The Denkard - which was not Zoroastrian Scripture but a religious manual - therefore favoured the solution of a leap-month once every 120 years, with a fall-back of adding 5 months after 600 years if this were missed. This practice was not, however, adopted by Zoroastrians living in Islamic Persia.

Many Zoroastrians migrated from the Middle East to India during the tenth century, becoming known in India as Parsis. They had knowledge of the Denkard's proposal: at some point between 1125 and 1129, the Parsi-Zoroastrians of the Indian subcontinent inserted such an embolismic month, named Aspandarmad vahizak (the month of Aspandarmad but with the suffix vahizak). That month would also be the last month intercalated: subsequent generations of Parsis neglected to insert a thirteenth month.

Around 1720, an Irani-Zoroastrian priest named Jamasp Peshotan Velati travelled from Iran to India. Upon his arrival, he discovered that there was a difference of a month between the Parsi calendar and his own calendar. Velati brought this discrepancy to the attention of the priests of Surat, but no consensus as to which calendar was correct was reached. Around 1740, some influential priests argued that since their visitor had been from the ancient 'homeland', his version of the calendar must be correct, and their own must be wrong. On June 6, 1745, a number of Parsis in and around Surat adopted the calendar which had continued in use of Iran, now to be identified as the Qadimi reckoning. Other Parsis continued to use the reckoning which had become traditional in India, and call their calendar Shahanshahi.