Schematic Dates for the Equinoxes, the Solstices and the Heliacal Phenomena of Sirius

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Fragment of a so-called “astrolabe text” from Nineveh featuring a circular schematic calendar indicating prominent stars and asterisms which rise in each month of the Babylonian calendar. (British Museum, London, tablet Sm. 162 [= CT XXXIII, nr. 11])

During the Seleucid period, the astronomical cuneiform tablets often list the predicted dates of the solar equinoxes and solstices and the heliacal phenomena of Sirius according to a scheme which is known as the “Uruk Scheme”. For each year in a 19-year cycle (of which year 1 = 1 SE) these phenomena were assumed to occur on a fixed date in the Babylonian calendar.

The scheme was calculated from an ideal sequence of summer solstice (SS) dates each separated by 12 months + 11;3,10 tithis. Although Babylonian astronomers were aware of the inequality of the length of the astronomical seasons, for calendrical purposes the dates for the begin of the other astronomical seasons were obtained by the successive addition of 3 months + 3 tithis.

The schematic dates for the heliacal phenomena of Sirius were obtained as follows:

In this scheme the heliacal rising of Sirius always fell in month IV (Duʾūzu), except in the 10th year in each 19-year cycle when it fell at the end of the previous month (Sīmannu).

year in
19-year
cycle		 vernal
equinox		 Sirius
heliacal
setting		 summer
solstice		 Sirius
heliacal
rising		 autumnal
equinox		 winter
solstice		 Sirius
acronycal
rising		 vernal
equinox
1   15 Ayyāru 29 Sīmannu 20 Duʾūzu   2 Tašrītu   5 Ṭebētu 10 Ṭebētu   8 Addāru II
2   26 Nīsannu 10 Sīmannu   1 Duʾūzu 13 Ulūlū 16 Kisilīmu 21 Kisilīmu 19 Addāru
3     7 Ayyāru 21 Sīmannu 12 Duʾūzu 24 Ulūlū 27 Kisilīmu   2 Ṭebētu 30 Addāru
4   18 Ayyāru   2 Duʾūzu 23 Duʾūzu   5 Tašrītu   8 Ṭebētu 13 Ṭebētu 11 Addāru II
5   29 Nīsannu 13 Sīmannu   4 Duʾūzu 16 Ulūlū 19 Kisilīmu 24 Kisilīmu 22 Addāru
6   10 Ayyāru 24 Sīmannu 15 Duʾūzu 27 Ulūlū 30 Kisilīmu   5 Ṭebētu  
7 3 Nīsannu 21 Ayyāru   5 Duʾūzu 26 Duʾūzu   8 Tašrītu 11 Ṭebētu 16 Ṭebētu 14 Addāru II
8     2 Ayyāru 16 Sīmannu   7 Duʾūzu 19 Ulūlū 22 Kisilīmu 27 Kisilīmu 25 Addāru
9   13 Ayyāru 27 Sīmannu 18 Duʾūzu 30 Ulūlū   3 Ṭebētu   8 Ṭebētu   6 Addāru II
10   24 Nīsannu   8 Sīmannu 29 Sīmannu 11 Ulūlū 14 Kisilīmu 19 Kisilīmu 17 Addāru
11     5 Ayyāru 19 Sīmannu 10 Duʾūzu 22 Ulūlū 25 Kisilīmu 30 Kisilīmu 28 Addāru
12   16 Ayyāru 30 Sīmannu 21 Duʾūzu   3 Tašrītu   6 Ṭebētu 11 Ṭebētu   9 Addāru II
13   27 Nīsannu 11 Sīmannu   2 Duʾūzu 14 Ulūlū 17 Kisilīmu 22 Kisilīmu 20 Addāru
14     8 Ayyāru 22 Sīmannu 13 Duʾūzu 25 Ulūlū 28 Kisilīmu   3 Ṭebētu  
15 1 Nīsannu 19 Ayyāru   3 Duʾūzu 24 Duʾūzu   6 Tašrītu   9 Ṭebētu 14 Ṭebētu 12 Addāru II
16   30 Nīsannu 14 Sīmannu   5 Duʾūzu 17 Ulūlū 20 Kisilīmu 25 Kisilīmu 23 Addāru
17   11 Ayyāru 25 Sīmannu 16 Duʾūzu 28 Ulūlū   1 Ṭebētu   6 Ṭebētu  
18 4 Nīsannu 22 Ayyāru   7 Duʾūzu 28 Duʾūzu 10 Ulūlū II 13 Kisilīmu 18 Kisilīmu 16 Addāru
19     4 Ayyāru 18 Sīmannu   9 Duʾūzu 21 Ulūlū 24 Kisilīmu 29 Kisilīmu 27 Addāru