This led him to suggest that vision occurs in the brain, rather than the eyes and that it is, therefore, subjective. He likened it to a camera obscura, a pinhole camera, and so suggested that images must also be inverted in the eye. Vision occurs when the Sun’s rays are reflected from objects and into our eyes.Īl-Haytham experimented with the laws of reflection and refraction using different shaped mirrors and lenses, and he accurately described how the eye functions as an optical instrument. Al-Haytham stated that light consists of tiny particles of energy that travel in straight lines and emanate from the Sun at a large but finite velocity. The Iraqi mathematician Ibn al-Haytham (also known as Alhazen) was the first person to correctly describe how perception occurs in about 1021 when he proved that light enters, but is not emitted by, the eye. Ī plot showing sin( θ), cos( θ), and tan( θ). Sin, cos, and tan waves could not be represented graphically until after the invention of the Cartesian coordinate system by Descartes and the French mathematician Pierre de Fermat in 1637. Hipparchus’ work was referenced by Ptolemy over 250 years later, and so it’s not known why he didn’t derive the sine law of refraction himself.

The ancient Greek astronomer Hipparchus created the first documented table of sine functions before 125 BCE. Tan( θ) = opposite length / adjacent length In the triangle above, sin( C) would equal length c / length c, which equals 1.

The sine of 90° is 1 because the opposite length will also be the longest, the hypotenuse. In Figure 2.3, sin( A) = length a / length c The sine of an angle ( θ) equals the ratio of two lengths - the length opposite the angle, and the longest length, the hypotenuse. The sine function shows how the angle inside a triangle changes as the lengths of its sides change. Reflection, Refraction, and DiffractionĢ0.

Angle of reflection diagram