السَّمْت

Azimuth derives from Arabic السَّمْت (as-samt), meaning 'the direction, the way, the path,' through Medieval Latin azimut and Old Spanish azimut. The word as-samt is the definite form of samt (direction, heading, path), used in Arabic astronomical texts to describe the horizontal direction to a celestial body — the angle measured along the horizon from north, moving clockwise. When European scholars translated Arabic astronomical texts into Latin in Spain and Sicily during the eleventh through thirteenth centuries, they routinely carried the Arabic definite article al- (here in the assimilated form as-) into the Latin transcription. The plural of as-samt in Arabic is as-sumūt, which medieval Latin transcriptions rendered as azimuth — the -uth ending being a garbled memory of the Arabic plural. Azimuth thus carries within it the preserved fossil of Arabic grammar.

Arabic astronomy in the medieval Islamic world was not merely a custodian of Greek knowledge but an active and innovative tradition. The House of Wisdom in Baghdad, founded in the early ninth century under the Abbasid caliphate, translated Ptolemy, Euclid, and Aristotle into Arabic and then extended their work substantially. Astronomers such as al-Battani (858–929 CE), who improved Ptolemy's measurements of the solar year and the length of the seasons, and al-Zarqali (1029–1100 CE), who worked in Toledo and designed the saphaea — a universal astrolabe working for any latitude — were producing original astronomical work of the highest quality. The Arabic astronomical terms that entered Latin — azimuth, zenith, nadir, algorism — are the vocabulary of this tradition.

In practical astronomy and navigation, azimuth is one of two coordinates — along with altitude, the angle above the horizon — that together specify the position of any object in the sky as seen from a particular location at a particular time. The pair forms the horizontal coordinate system, which is observer-centered and changes continuously as Earth rotates, making it less fundamental than the equatorial coordinate system (right ascension and declination) for cataloguing stellar positions. But the horizontal system is immediately practical for navigation and for pointing telescopes and instruments: if you know an object's azimuth and altitude, you can point a telescope at it. Military artillery also uses azimuth as the standard bearing reference for targeting.

The word azimuth appears directly in the names of modern instruments and systems. The azimuth drive of a telescope moves the instrument along the horizon; the alt-azimuth mount — the simplest type of telescope mount — moves independently in altitude and azimuth. The Global Positioning System reports azimuth to describe the horizontal direction from your position to a satellite. In architecture and urban planning, solar azimuth analysis determines how sunlight will fall on buildings at different times of year, influencing passive solar design and window placement. The Arabic 'way' or 'path' has become the vocabulary of any discipline that needs to specify horizontal direction: gunnery, navigation, astronomy, architecture, and GPS all use the same word that Baghdad astronomers used to describe how far around the horizon a star had traveled.