The Months of the Babylonian Calendar

Nr.	Month names								Approximate equivalent in the Julian calendar
	Babylonian		Hebrew	Old Persian	Achaemenian Elamite	Elamite	Macedonian(#)
							earlier correlation	later correlation
I		Nīsannu	Nīsān	Ādukanaiša	Hadukannaš	Zikli	Artemisios	Xanthikos	March-April-May
II		Ayyāru	Iyyār	Θūravāhara	Turmar	Zarpakim	Daisios	Artemisios	April-May-June
III		Sīmannu	Sīwān	Θāigraciš	Sākurriziš	Hadar	Panemos	Daisios	May-June-July
IV		Duʾūzu	Tammūz	Garmapada	Karmabataš	Hallime	Loös	Panemos	June-July-August
V		Ābu	Āb	???	Turnabaziš	Zillatam	Gorpiaios	Loös	July-August-September
VI		Ulūlū	Elūl	???	Karbašiyaš	Belilit	Hyperberetaios	Gorpiaios	August-September-October
VII		Tašrītu	Tišrī	Bāgayādiš	Bakeyatiš	Manšarki	Dios	Hyperberetaios	September-October-November
VIII		Araḫsamna	Marḥešwān	*Vrkazana	Markašanaš	Lankelli	Apellaios	Dios	October-November-December
IX		Kisilīmu	Kislēw	Āçiyādiya	Hašiyatiš	Šibari	Audynaios	Apellaios	November-December-January
X		Ṭebētu	Ṭēbēt	Anāmaka	Hanamakaš	Šermi	Peritios	Audynaios	December-January-February
XI		Šabāṭu	Šebāṭ	*Θwayauvā	Samiyamaš	Kutmama	Dystros	Peritios	January-February-March
XII		Addāru	Adēr	Viyax(a)na	Miyakannaš	Aššetukpi	Xanthikos	Dystros	February-March-April

# epigraphical and numismatical sources indicate that, between 31 CE and 46/47 CE, the correlation
of the Macedonian months with the Babylonian months underwent a shift of one month

Regulating the Calendar

In order to keep the Babylonian calendar aligned with the seasons various intercalation schemes were employed.

• Initially, the insertion of an intercalary month was probably decided by considering various non-astronomical signs, such as the weather, the flight of migratory birds, the ripening of fruits and crops, etc.
• Later the insertion of an intercalary month appears to have based on the observation of the heliacal rising of certain stars such as MUL.MUL (Pleiades) or MUL.KAK.SI.SA (Sirius). Continued observations of the heliacal rising of selected stars probably led to the discovery of regular intercalation patterns such as the 8-year and 19-year cycles.
• After about 535 BCE regular intercalation schemes were used, first the octaeteris (with three intercalary months in every eight years) and, after about 500 BCE, the 19-year cycle (with seven intercalary months in each cycle). Counting from the first year of Nabonassar (747 BCE), the years 3, 6, 8, 11, 14 and 19 were augmented by adding an extra Addāru [Addāru šanû = Addāru II = XIIb] at the end of the year and an additional Ulūlū [Ulūlū šanû = Ulūlū II = VIb] in the middle of year 17 [counting from 1 SE, the begin of the Seleucid Era, the intercalary years were 1, 4, 7, 9, 12, 15 and 18 in each 19-year cycle].

The Spring Equinox and the Begin of the Babylonian Year

According to the calendrical tables of Parker & Dubberstein (1971), the date of the Babylonian New Year was closely linked with that of the spring equinox.

Initially, during the Neo-Babylonian Period, the Babylonian New Year tended to fall slightly before the spring equinox but after the Achaemenids gained control of Mesopotamia and introduced the 19-year intercalation cycle the Babylonian New Year dates gradually shifted until they fell on or after that of the spring equinox.