7. The Nature of Energy Received from the Sun: Figuring out What Light Really is

Light has many peculiar properties, some with analogs in water waves, some with analogs in sound waves, and some that are unique. It was discovered that ‘white’ light passing though a glass prism is split into a spectrum showing all of the colors of the rainbow. These can be recombined to make white light. Some thought that light traveled instantaneously through space, but measurement of its speed, already close to the modern value, was made in the Seventeenth Century. It was discovered that there was invisible radiation coming from the Sun, beyond the red (infrared) and violet (ultraviolet) ends of the spectrum. Light had many strange properties: reflection, refraction, dispersion, diffraction, and polarization. It was discovered that the colors travel at different speeds through media like minerals or glass. While investigating the relation between electricity and magnetism, James Clark Maxwell realized that light was an electromagnetic wave. It was thought to be moving through the ‘luminiferous æther’ that filled all of space. But attempts to detect the ‘æther’ failed. Empty space was truly empty!