How do we know what stars are made of?

How do astronomers know what stars are made of when those stars are light years away from Earth? These demonstrations by Dr Francisco Diego reveal the colors of light that are produced from sodium chloride, rubidium chloride, and copper sulfate, hinting at how we identify the chemical compositions of those distant stars. File under astronomical spectroscopy:

Newton used a prism to split white light into a spectrum of color, and Fraunhofer’s high-quality prisms allowed scientists to see dark lines of an unknown origin. It was not until the 1850s that Gustav Kirchhoff and Robert Bunsen would describe the phenomena behind these dark lines—hot solid objects produce light with a continuous spectrum, hot gasses emit light at specific wavelengths, and hot solid objects surrounded by cooler gasses will show a near-continuous spectrum with dark lines corresponding to the emission lines of the gasses. By comparing the absorption lines of the sun with emission spectra of known gasses, the chemical composition of stars can be determined.

via @AlomShaha.