Nibiru (Babylonian astronomy)

Nibiru (also transliterated Neberu, Nebiru) is a term in the Akkadian language, translating to "crossing" or "point of transition", especially of rivers, i.e. river crossings or ferry-boats.
In Babylonian astronomy, the term Nibiru (in cuneiform spelled dné-bé-ru or MULni-bi-rum) refers to the equinox and the astronomical objects associated with it.

Role in Babylonian cosmology
Nibiru was considered the seat of the summus deus who shepherds the stars like sheep, in Babylon identified with Marduk. The establishment of the nibiru point is described in tablet 5 of the creation epic Enûma Eliš: “When Marduk fixed the locations (manzazu) of Nibiru, Enlil and Ea in the sky".
The Enûma Eliš states:

Nibiru is described more closely on a complete cuneiform tablet:
 
Böhl calls the text "objectively the most difficult passage, although it has been handed down in its entirety. The Nibiru tablet does not provide any essential help for the clarification."

In the enumerations, Nibiru is mentioned at different astronomical locations in conjunction with the positions of stars and planets, mostly as the "star of Marduk", however, the various stars or planets were not subject to any fixed interpretation. For example, the "star of Ea" was described at various "revelation spots" including Vela, Fomalhaut, and Venus. Similar interpretations were made for the other "stars of the gods", so multiple celestial coordinates must be considered.
Nibiru has been associated with the area of Libra. The Nibiru constellation rose in the month of Tišritum, around autumnal equinox. However Nibiru was also a name for the planet Jupiter 
when observed in the month of Tišritum.
In the MUL.APIN, Nibiru is identified as Jupiter:

Conversely, Tablets K.6174:9’ and K.12769:6’ refer to it as Mercury: "If Mercury (MULUDU.IDIM.GU4) divides the sky and stands there, [its name] is Nibiru."

In a 2015 report for the Cuneiform Digital Library Bulletin, Immanuel Freedman analyzed the extant cuneiform evidence and concluded that the hypothesis that the name Nēbiru may be assigned to any visible astronomical object that marks an equinox is supported by cuneiform evidence.

References 

Literature
  A. Schott, Marduk und sein Stern, Zeitschrift für Assyriologie 43 (1936), 124-145.
  Johannes Koch, Der Mardukstern Neberu, Welt und Oriens 22 (1990), 48-72.

Category:Babylonian astronomy
Category:Enûma Eliš
Category:Mesopotamian deities