Final answer:
A spectrograph is used in astronomy to measure the spectrum of celestial objects, providing details about composition, temperature, and motion. Through spectroscopy, astronomers interpret the interaction of light with matter, deducing various characteristics of stars and galaxies from collected data.
Step-by-step explanation:
A spectrograph is usually used in astronomy to measure the spectrum of celestial objects, which can reveal important information about their composition, temperature, motion, and many other characteristics. Spectroscopy, the method by which a spectrograph operates, deals with how light interacts with matter. By analyzing the absorption and emission lines within the spectrum, astronomers can identify the chemical elements present. This has been a fundamental aspect of astronomical research since it was first used to link the spectral lines in the Sun with the known elements on Earth. The use of spectrographs has significantly progressed since the pioneering work of nineteenth-century scientists like Joseph Fraunhofer and Sir William Huggins, making spectroscopy a cornerstone in understanding physical properties of celestial entities.
Furthermore, spectra variations due to atmospheric pressure can hint at a star's size, and shifts in spectral lines caused by the Doppler effect can provide information about a star's radial velocity and rotational velocity. Such data are vital, given that astronomers cannot interact with stars and galaxies directly and must rely on light to study these distant objects. Modern technology has greatly enhanced the efficiency of measuring spectra as exemplified by the Sloan Digital Sky Survey's automated process, a leap from the tedious, manual methods of the past.