Starlight unravels in a prism and reveals its true colors.
Light paints nature in marvelous colors thanks to absorption and reflection. However, we are always surrounded by white light: who would have guessed that it consists of many colors instead? Newton followed his intuition and devised an optical prism that can unravel these hidden colors, called spectrum. Centuries later, scientists used similar ideas to study light emitted by stars. They eventually discovered that the spectrum of a star reveals important information about its chemical composition. In fact, every element absorbs a different frequency, or color, of light. These absorptions can be detected on Earth as dark lines in the color spectrum, revealing the distinctive fingerprint of a star.
How our understanding of light has evolved from the greeks to the 21st century.