Human beings' color vision allows us to distinguish both large and subtle differences between objects of similar color. Consider a forest, with its multitude of greens. But objects with similar colors are not necessarily the same, as the jade and seaweed found on some Pacific coast beaches illustrate. Researchers, chemists, criminalists, and many other investigators study and compare objects and learn about their compositions by breaking the light down into its composite colors, a technique called spectroscopy
(pronounced spek-TRAH-skah-pee). Most people are familiar with a natural presentation of the spectrum (plural: spectra) of the Sun: we call it a rainbow.