Alhazen
Alhazen
965 — 1039
Arab mathematician, physicist, and astronomer born in Basra around 965 and died in Cairo in 1039. Considered the father of modern optics, he revolutionized the understanding of light and vision. His major work, the Kitāb al-Manāẓir, profoundly influenced European scholars of the Middle Ages.
Key Facts
- Born around 965 in Basra (present-day Iraq) and died around 1039 in Cairo
- Wrote the Kitāb al-Manāẓir (Book of Optics) around 1011–1021, translated into Latin in the 12th century
- Demonstrated that vision results from light reflected by objects into the eye, refuting Greek theories
- Invented the camera obscura to study the rectilinear propagation of light
- A pioneer of the experimental method, he based his conclusions on observation and experimentation
Works & Achievements
A landmark scientific work in seven volumes that revolutionized the theory of vision and light, demonstrating through experiment that light travels from objects to the eye. Translated into Latin in the 12th century, it profoundly influenced Roger Bacon, Kepler, and Descartes.
A short treatise devoted to the nature of light, in which Alhazen demonstrates that the Moon is a sphere that reflects sunlight, and that every light source emits in all directions.
A treatise on physical astronomy that seeks to reconcile Ptolemy's mathematical models with a physical reality of the celestial spheres, foreshadowing later debates on the structure of the universe.
A treatise reflecting the breadth of Alhazen's interests, in which he also explored music theory in connection with mathematics and acoustics.
A work on statics and the principles of the balance, illustrating the experimental and mathematical approach that Alhazen applied across all areas of physics.
Alhazen measured and analyzed the refraction of light in the atmosphere, estimating its height at approximately 15 km — a value remarkably close to modern measurements.
Anecdotes
Alhazen, hoping to convince the Fatimid caliph Al-Hakim to fund a project to regulate the flooding of the Nile, proposed an ambitious system of dams. But once he arrived in Egypt, he realized the project was technically unfeasible. Fearing the caliph's wrath, he feigned madness for several years until Al-Hakim's death in 1021.
To prove his theory of vision, Alhazen built the first experimental camera obscura in history: a darkened room with a small hole that let light through. He observed the inverted image of the outside world projected onto the opposite wall, demonstrating that light travels in straight lines.
Unlike Greek scholars such as Euclid and Ptolemy, who believed the eye emits rays of light toward objects, Alhazen experimentally demonstrated the opposite: it is light reflected by objects that enters the eye. This conceptual revolution permanently transformed our understanding of vision.
Alhazen was one of the first thinkers to apply a rigorously experimental method to science. He repeated his experiments, varied the conditions, and recorded his observations with precision — an approach that foreshadows the modern scientific method by several centuries, long before Galileo and Descartes.
Primary Sources
Light travels in straight lines from every point of a luminous object in all directions. The eye perceives objects by means of the light rays that emanate from them and enter the eye.
The light of the sun and the light of the moon are of the same nature; the moon merely reflects sunlight. Every luminous body emits its light in all directions in a spherical manner.
Celestial bodies are solid spheres whose movements are regular and circular, and their arrangement can be deduced through reason and observation.
Alhazen measured the density of air and estimated the height of the atmosphere at approximately ten miles, by observing the duration of twilight.
Key Places
Alhazen's birthplace and a major intellectual and commercial center of the medieval Islamic world, where he received his early scientific and mathematical education.
The city where Alhazen spent most of his adult life, near the Fatimid Dar al-Hikma; it was here that he wrote his major works, including the Kitāb al-Manāẓir.
Capital of the Abbasid Caliphate and a world center of learning in Alhazen's era, home to the famous House of Wisdom where Greek and Persian texts were translated and compiled.
Alhazen proposed a flood regulation project on the Nile to Caliph Al-Hakim; after recognizing the technical impossibility of the undertaking, he feigned madness to escape the caliph's wrath.
Gallery
Cosmos, a sketch of a physical description of the universe
Wikimedia Commons, Public domain — Humboldt, Alexander von, 1769-1859. n 80051862 Otté, E. C. (Elise C.) n 87133724 Paul, Benjamin H. (Benjamin Horati
The complete photographer,
Wikimedia Commons, Public domain — Child Bayley, R. (Roger), 1869-
Living pictures : their history, photo-production and practical working, with a digest of British patents and annotated bibliography
Wikimedia Commons, Public domain — Hopwood, Henry V. (Henry Vaux), 1866-1919
Memoirs of the life of Nicholas Poussin
Wikimedia Commons, Public domain — Callcott, Maria, Lady, 1785-1842 Clark, I., fl. 1772-1824 Fénelon, François de Salignac de La Mothe-, 1651-1715 Fry
Visual illusions, their causes, characteristics and applications
Wikimedia Commons, Public domain — Luckiesh, Matthew, b. 1883
Ibn al-Haytham
Wikimedia Commons, CC BY-SA 4.0 — Sopianwar
Hazan
Wikimedia Commons, Public domain — artwork drawn by Adolph Boÿ, engraved by Jeremias Falck
Ibn al-Haytham
Wikimedia Commons, Public domain — unknown, probably Muhammad Atiyya Al-Ibrashi (1897 –1981).
Ibn Al-Haytham portrait
Wikimedia Commons, CC BY-SA 4.0 — Michel Bakni
ImageVI’s - the software that collects the vegetation indices you need - user manual
Wikimedia Commons, CC BY 4.0 — Adriano Aparecido Virgílio, Adriano Rogerio Bruno Tech, Lilian Elgalise Techio Pereira