Azimuth

Definition

Azimuth is the horizontal-coordinate angle measured along the observer's local horizon, usually from due north clockwise through east, south, and west, locating where a celestial body rises, transits, or sets relative to a fixed terrestrial reference. Together with altitude (the angle above the horizon) it forms the local horizontal coordinate system used by observational astronomy and archaeoastronomy. Because the azimuth of a star's rising-point depends on the observer's latitude and on the star's declination, it shifts slowly with precession and substantially with latitude.

In Tradition

In the observational-astronomy traditions underlying Western astrology, azimuth is treated as the horizon-frame measurement relating a celestial event to a specific direction on the ground. Belmonte and Lull use azimuth as the principal data-point in reconstructing Egyptian temple alignments to solar, stellar, and lunar events. Koch-Westenholz documents the Babylonian Three Ways of the Sky (Anu, Enlil, Ea) as a horizon-based stellar geography whose membership 'depended on where they rose on the Eastern horizon' — defined by azimuth ranges.

In Practice

Practitioners use azimuth in three connected contexts. First, archaeoastronomical reconstruction: temple-orientation studies measure a building's principal axis and read it against the azimuth of a sunrise, sunset, lunastice, or heliacal star-rising on a culturally significant date. Belmonte-Lull document Hatshepsut's Djeser-Djeseru at Deir el-Bahari at an azimuth of 115½° as a deliberate alignment to sunrise on the Nehebkau Festival (I Peret 1) c. 1460 BC; the Naga Apedemak temple at azimuth 119.5° is read as aligned to the southernmost moonset position. Second, ancient observational record-keeping: MUL.APIN II i 12 records the Sun's daily azimuthal shift between solstitial and equinoctial rising-points as forty NINDA per day, the schematic measurement summing to 7200 NINDA (= 120 UŠ) across the 180-day half-year. Third, modern astrological astronomy uses azimuth alongside altitude for the parans method of fixed-star calculation and for any computation tied to the local horizon rather than the ecliptic.

Historical Origin

Azimuth-based observation is documented in Babylonian schematic-astronomy texts (MUL.APIN, second-millennium baseline with first-millennium canonical compendium) and in Egyptian archaeoastronomical reconstruction back to the 18th-Dynasty Djeser-Djeseru c. 1460 BC. Koch-Westenholz cites J. Koch (1989) on the MUL.APIN II Paths-of-Anu/Enlil/Ea azimuth scheme. The Arabic word al-samt ('the direction') survives into European languages as the technical term — English azimuth, French and Spanish azimut — entering Latinate astronomy through medieval Arabic astronomical texts.

Etymology

Origin: Arabic. Meaning: Direction, way.

Further Reading

• Juan Antonio Belmonte & José Lull, Astronomy of Ancient Egypt
• Hermann Hunger & John Steele, MUL.APIN
• Ulla Koch-Westenholz, Mesopotamian Astrology