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Spectroscopy is the study of the interaction between light and matter. Spectrometry is the measurement of these interactions and an instrument which performs such measurements is a spectrometer or spectrograph. A plot of the interaction is referred to as a spectrum. Historically, spectroscopy referred to a branch of science in which visible light was used for the study of the structure of matter and for qualitative and quantitative analyses. Recently, however, the definition has broadened as new techniques have been developed that utilise not only visible light, but many other forms of radiation. Spectroscopy is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from or absorbed by them. Spectroscopy is also heavily used in astronomy and remote sensing. Most large telescopes have spectrometers, which are used either to measure the chemical composition and physical properties of astronomical objects or to measure their velocities from the red shift of their spectral lines.