Exploring the Universe with Spectroscopy
While astronomers were starting to use photography to capture light from celestial objects, they were also learning how to analyze light itself. They found that an object's spectrum, the rainbow of colors that forms when light passes through a prism, could tell them what the object was made of and how it moved. By the late 1920s the use of spectroscopy, creating and studying spectra, produced an amazing discovery: the Universe of galaxies was expanding.