Spectroscopy is the study of the absorption and emission of light by atoms and molecules, and how this relates to the wavelengths of light. It is a science of the spectrum, a set of energy bands of varying wavelengths (colours) produced by electromagnetic radiation. It is typified for a visually oriented species like humans by the rainbow band of colours that emerges when you pass white light through a prism (or sunlight through raindrops). This property of light became the domain of Isaac Newton in the late 17th century. In his 1704 masterpiece of theoretical dualism, Opticks, Newton defined many of the ground rules 200 years before spectroscopy was first seriously applied.
It’s amazing how progress in astronomy has followed in huge leaps upon the development of new observational technology. The Middle Eastern scholars of the first five hundred years AD gave us the basis for mapping the sky when they devised the concept of degrees of arc—the novel idea that cycles can be represented by circles, quantitatively divided up into equal segments we today call degrees. They also invented the astrolabe, an instrument for measuring celestial angles. This technology carried us through the revelations of Copernicus, the eye-watering accuracy of Tycho Brahe’s observational catalogues, and subsequent analysis by Johann Kepler which resulted in our understanding of orbital motion and which led ultimately to Newton’s laws of motion and gravitation.