MUL.APIN
The MUL.APIN (also written as mulAPIN) is a significant Babylonian astronomical compendium. It is generally considered to be the most important source of information regarding Babylonian astronomy and calendrical systems for the period of the Old Babylonian Empire through the Neo-Babylonian period.
The title MUL.APIN derives from the standard Mesopotamian convention of naming a work after its incipit, or first line: "MUL.APIN u4-še ba-ab-bar-ra..." which translates roughly to "If the Plough star and the Sun are in..." The compendium is organized into two main tablets, with a number of supplementary sections.
The MUL.APIN is not a work of theoretical astronomy or mathematics. Rather, it is a descriptive catalog of celestial phenomena and their calendrical implications. It focuses on observations of the rising and setting of stars, constellations, and planets, providing lists of constellations that rise and set at the same time of year, as well as the intervals between their heliacal risings (the first visible appearance of a celestial object after a period of being too close to the sun to be seen).
The text provides rules for regulating the lunar calendar, including instructions on how to insert leap months to keep it synchronized with the solar year. It also contains information about the solstices and equinoxes.
The MUL.APIN is valuable to modern scholars because it offers insight into the observational methods and astronomical knowledge of the Babylonians, revealing their understanding of the cyclical nature of celestial events and their use of that knowledge for practical purposes such as agriculture and timekeeping. While the exact dating of the oldest known version of the MUL.APIN is debated, scholars generally place its origins in the early part of the first millennium BCE, based on the astronomical information contained within it. Several copies and fragments of the text have been discovered, providing a basis for reconstructing and interpreting the original work.