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# What is the difference between physical and geometrical optics?

Many ancient cultures that worshiped the sun believed that the sudden eclipse of the sun was a terrible occurrence. These events did not happen very often, but when solar eclipses did occur and darkness set in on the area, worshipers would gather and pray, often for days, to the sun gods. During the Zulu War in South Africa Zulu warriors massacred a British battalion. During the afternoon of the battle there was a solar eclipse. The Zulus named the day of the battle, January 22, 1879, the day of the dead moon.

Because eclipses were often either recorded or suggested in ancient myths or documents, solar eclipses can be used to find the date and place of events recorded in these documents. For example, in the sixth century B.C.E., the Medes and Lydian armies were in a war when a solar eclipse occurred. The eclipse halted the battle and helped bring about a peace between the two armies because they thought that the disappearance of the sun was an omen. A candidate eclipse was on May 28, 585 B.C.E., near the Halys River in modern Turkey.

In an Indian epic story, Arjun vowed to kill Jayadrath to avenge Jayadrathâ€™s killing of Abhimanyu. During a solar eclipse Jayadrath came out of hiding to celebrate his survival, but when the sun reappeared Arjun killed him. Eclipses occurred in this region in 3129 B.C.E. and 2559 B.C.E., thus providing two possible dates for the event.

Geometrical optics deals specifically with the path that light takes when it encounters mirrors and lenses. Geometrical optics uses the ray model of light in which an arrow represents the direction light travels. The ray model does not consider the wave nature of light. Ray diagrams trace the path that light takes when it reflects and refracts in different media.

Physical optics, on the other hand, is the division of optics that depends on the wave nature of light. It involves polarization, diffraction, interference, and the spectral analysis of light waves.

Reflection occurs when light bounces off a surface, whether it is a piece of paper or a mirror. Shiny metals and very still water make good reflectors, creating images that resemble objects from which the light is coming.
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