In Mesopotamia, the Akitu Festival marks of the sowing of barley in the autumn and the reaping of barley in the spring. In this period, starting say, 3200BC in Uruk, the Sun at the vernal equinox used rise in the constellation of the Bull, Gugalanna, now known as Taurus - effectively the constellation is invisible in the blaze of the sun. This is the beginning of civilisation and the activities focused on the priest-king, are choreographed by the priesthood as they interpret the sacred movements of the seven planets (the lordly moon with his court of the sun and the planets visible with the naked eye, Mercury,Venus, Mars, Saturn and Jupiter).
The annual lament for Dumuzi (the shepherd-fisherman- spouse of Inanna) occurs in the summer when the sun shrivels the meadows and the livestock no longer provide milk. In a reversal of the later role of Persephone, it is Dumuzi who spends half the year with Inanna in the daylight world and half in the netherworld where her dark sister, Ereshkigal, was sovereign- at least in the early period.
Shamash, the Sumerian sun god, rises in the morning over the Zagros Mountains with his distinctive rays of light emanating from his shoulders and carrying his distinctive saw toothed weapon. The Morning Star, the goddess Inanna, is visible above the mountain peaks and the World Tree, or Axis Mundi, around which the constellations spin, is visible to her left.She appears to proffer something to Shamash.
The god, Ninurta, in this context probably in his role of god of South Wind and subduer/ of the storm god Zu,. Enki (Ea), Lord of the Apzu, realm of the fresh waters, approaches dramatically from the opposite direction carrying the storm god, Imdugud or Zu and appears to spill onto the mountain peaks from which arise the great rivers of the Euphrates and Tigris with their teeming shoals of fish. Although the rainy season is in winter, the snows on top of the Zagros and Taurus mountain ranges melt in spring swelling the Euphrates, Tigris and Karun rivers. Behind him stands the vizier of the underground realm of fresh waters, Usmu. The crowns of the gods are made up of stylised stacked (bull?) horns.
Speculating astronomically, we may be looking at: Ninurta in the generic role of the hunter/hero (a Gilgamesh or Enkidu) represented by the constellation Orion accompanied by a lion representing the constellation Leo - although the constellation Canis Major with with the Dog Star, Sirius, is the actual constellation following at his heel and the zodiac as we know it is mainly based on Ptolemy's (of Alexandria) description and so the original Babylonian zodiac may have been different.
In this context Enki may represent the constellation Capricornus . Beneath his foot sits the bull, Gugulanna, signifying the constellation of Taurus obscured by the rising sun as indeed the sun did rise in the constellation of Taurus in spring time. And yes there is an Aquila constellation which is particularly prominent in summer and above Capricorn. Finally we would have Usmu, Enki's vizier with his two faces like the Roman god, Janus (January), signifying perhaps the constellation of the water carrier, Aquarius. See Zodiac of Constellations to see the relation of the constellations to each other. Of Capricorn, Aquarius and Piscies, Jay Pasachoff in his book, Stars and Planets p132 writes,
The last three constellations of the zodiac are in the region called the Sea.
It may simply be that the appearance of the planet Venus as morning star at the time of the Akitu festival signified a particularly fortuitous correspondence of the celestial spheres and that is what is here recorded.
There may too be in this image a precursor of the four evangelists as lion, hunter (angel), eagle and bull bear witness to the central drama.
There is of course no substitute for being in Sumer in the third Millennium BC and watching the sun and the constellations rise in the sky. Using the free software, Stellarium, we did up the following slide show following the constellations as they move above the eastern horizon in Sumer over a twenty four hour period in the year 2500BC.