The geometry of light: Galileo's Telescope, Kepler's Optics

The Geometry of Light provides readers access to pioneering ideas about light, vision, and the telescope as they appear in Johannes Kepler's book Dioptrice. Kepler's book beautifully illustrates the power of elementary geometry to explain the physical world. But Kepler wrote for fellow mathematicians, not a general audience. The Geometry of Light makes Kepler's ideas accessible to anyone who has studied high school geometry.
Johannes Kepler was a giant of seventeenth-century science. A contemporary of Galileo, Kepler is principally known as a founder of modern astronomy. His work in theoretical astronomy complemented Galileo's observations in promoting the heliocentric model of the solar system.
In 1609, Galileo heard reports of an invention that made distant objects appear close. Galileo proceeded to construct his own telescope, and discovered that four moons rotated around Jupiter. This was a direct refutation of the prevailing belief that all heavenly bodies rotated around Earth.
Inspired by Galileo's use of the telescope, Kepler developed a theory of lenses that served as a basis for rational telescope design. He published this work in a short book titled Dioptrice. Kepler perceived that the telescope produced its effect by means of the refraction of light. In Dioptrice, Kepler explains how the refraction of light results in the magnification of distant objects.
Kepler's geometric approach conveys an intuitive grasp of optics that is hard to obtain using modern methods. In addition, Kepler's theory of lenses has a special charm because it achieves so much with so little. It is truly a breathtaking experience to follow Kepler as he deftly lays the foundations of modern optics using only a few simple principles.