By: Mir M.Hosseini
While cities of the Achaemenid Empire were being captured one after another by Macedonian Alexander, among many booties recovered from the Persian civilization, Iranian achievements in science and technology were quickly adopted by the Greeks. It is important to note that even a simple innovation such as arming Hoplites with longer spears had changed the power balance and led to downfall of the Achaemenid Empire.
Greeks started translating astronomical diaries after conquering Babylon following the Battle of Gaugamela in 331 B.C. The new knowledge was immediately applied in Greece: the astronomer Callippus of Cyzicus, a pupil of the philosopher Aristotle of Stagira, recalculated the length of the lunar month and proposed a new calendar, in which he applied the longer cycle. His new era, which was used by all later Greek astronomers, started on June, 28 330 B.C., eight months after the capture of Babylon and right after the falls of Rhagae.
Dariush the Great introduced a standard procedure for the intercalation of months to Babylonian priests in 503 B.C. however the origin of Persian Calendar goes back to a few millennia earlier. Iranians have always observed Equinox as measuring point of the year. Spring Equinox coincides with Norooz and Autumn Equinox is the point of mid-year.
Achaemenid solar month names and their perceived modern equivalents are as follows:
Application of Achaemenid month names can be seen in the Bisotoun Inscription. Persians had also solved the problem of adopting solar calendars to twelve lunar months by adopting a standard system.
After translating Achaemenid Chronicles, Callippus started his observation cycle on the summer Solstice, 330 BC, (28 June in the Proleptic Julian calendar). The cycle's begin position, the stellar position and sidereal hour timing the eclipse, are used by later astronomers for calibrating their observations in relation to subsequent eclipses.
The original Achaemenid Calendar evolved in time into modern Persian Calendar. The Sassanid adopted the Yazdgerd calendar. The solar Jalali calendar was adopted on March, 15 1079 A.D. in respect to Muslim lunar calendar. The modern Persian calendar was adopted in 1925, supplanting (while retaining the month names of) a traditional calendar dating from the eleventh century. The calendar consists of 12 months, the first six of which are 31 days, the next five 30 days, and the final month 29 days in a normal year and 30 days in a leap year.
The Persian solar calendar still has the highest precision among all available systems.