Skip to content
SHAXS
Suggest an edit

Al-Saghani

Tenth-century astronomer and mathematician in Baghdad who devised a distinctive projection of the sphere for the astrolabe and worked at Sharaf al-Dawla’s observatory.

Occupation:
Scientist, Mathematician, Astronomer
Real name:
Abu Hamid Ahmad ibn Muhammad al-Saghani al-Asturlabi
Died:
990
Birthplace:
Surkhandarya

Biography

Abu Hamid Ahmad ibn Muhammad al-Saghani al-Asturlabi was a mathematician and astronomer of the tenth century who worked in Baghdad. His by-name al-Asturlabi, “the astrolabe maker”, points to his craft: he built and described that instrument. The nisba al-Saghani ties him to Saghaniyan (Chaghaniyan), a historic region that lay in what is now Uzbekistan’s Surkhandarya Province; Uzbek publications place his homeland around Denau. Other sources, including the Biographical Encyclopedia of Astronomers, name the village of Saghan near Merv as his birthplace. His year of birth is not known.

Almost nothing is recorded about his youth. He is known to have gone to Baghdad, then the greatest centre of learning, to pursue science, and there he studied astronomy and geometry. The thirteenth-century biographer al-Qifti describes him as an expert in geometry and the science of the heavens and a maker of observing instruments, and says he had students.

His principal work is a treatise on projecting the celestial sphere onto the plane of the astrolabe, written for the ruler Adud al-Dawla (977–983). In twelve sections the author sets out a method of his own in which the centre of projection lies not at a pole but at another point on the sphere’s axis, so that the plate carries not only circles and straight lines but ellipses, parabolas and hyperbolas. Al-Biruni explicitly named al-Saghani as the inventor of this projection.

He also wrote a treatise on the hour lines of astrolabe plates (only its first chapter survives), a treatise on constructing a regular heptagon, a three-part work on the distances and sizes of the heavenly bodies, and several geometrical studies. According to al-Biruni, al-Saghani measured the obliquity of the ecliptic and the latitude of Baghdad with a ring divided at five-minute intervals, at a place called Birkat al-Zalzal in the west of the city.

In 988 he was among the astronomers of the observatory that the Buyid ruler Sharaf al-Dawla had set up beside the palace garden in Baghdad; the Sun’s entry into Cancer and Libra was recorded in two documents, and al-Saghani signed them. He died in Baghdad in 990. Al-Biruni, Ibn Iraq and al-Sijzi drew on his measurements, and twentieth-century scholars such as F. Rosenthal, R. Lorch and J. Hogendijk studied his treatises from the manuscripts.

Career

Life path

  1. 10th century
    Birth

    Born in Saghaniyan (Chaghaniyan); the year is unknown. Some sources give the village of Saghan near Merv as his birthplace.

  2. 10th century
    Move to Baghdad

    Went to Baghdad, the leading centre of learning of the age, to study astronomy and geometry, and became an astrolabe maker.

  3. 977–983
    Treatise on projecting the sphere

    Wrote for the ruler Adud al-Dawla a work on a special projection of the celestial sphere onto the plane of the astrolabe.

  4. 984–985
    Measurements in Baghdad

    According to al-Biruni, determined the obliquity of the ecliptic and the latitude of Baghdad at Birkat al-Zalzal in the west of the city.

  5. 988
    Sharaf al-Dawla Observatory

    Counted among the astronomers of the Baghdad observatory; signed the records of the observations of the Sun’s entry into Cancer and Libra.

  6. 990
    Death

    Died in Baghdad.

Works

  • “On the Manner of Projecting the Sphere onto the Plane of the Astrolabe”
    Astrolabe treatise

    A work in twelve sections dedicated to Adud al-Dawla; it sets out a new projection that yields ellipses, parabolas and hyperbolas on the plate.

  • “Treatise on the Hours Marked on Astrolabe Plates”
    Astrolabe treatise

    On the arcs of the hour lines; only the first chapter survives, edited and studied by J. Hogendijk.

  • “Treatise on Constructing a Regular Heptagon in a Circle”
    Geometrical treatise

    On constructing the side of a regular heptagon inscribed in a circle.

  • “On the Distances and Sizes of the Heavenly Bodies”
    Astronomical work

    A three-part work on the distances to the luminaries and their sizes.

  • “Book of the Rules of the Science of Astronomy”
    Astronomical work

    Mentioned by al-Biruni; it reports the author’s own measurements made in Baghdad.

  • “Treatise on the Trisection of the Angle”
    Geometrical treatise

    A study of dividing an angle into three equal parts.

Legacy

Al-Biruni regarded al-Saghani as the inventor of the projection of the sphere onto the astrolabe plane with a centre of projection off the pole, and used his measurements; Ibn Iraq and al-Sijzi drew on his work. Al-Saghani also left some of the earliest reflections on the history of science, comparing the achievements of the “ancients” and the “modern” scholars. His surviving treatises were edited and discussed in the twentieth century (R. Lorch, J. Hogendijk).

Era: Baghdad under the Buyids, tenth century
  • The Sharaf al-Dawla Observatory in Baghdad records its observations; al-Saghani signs the documents (988)
Al-Saghani — Scientist | Shaxs.uz