During his time in Benediktbeuern, Fraunhofer made experiments with glass. He discovered very important things about light. One day Fraunhofer was playing with a piece of glass called a "prism" and a telescope in a room full of sun light. When he used the telescope to look at the glass he discovered that he could see all colours of the rainbow. But there were black lines between the colours. Fraunhofer never discovered what the black lines were; he suggested they might be boundaries between different colors. Many years later, scientists discovered that these black spectral lines existed because some materials that exist in the sun and in the sky can absorb parts of the light. Today scientists use a similar technique to discover what chemicals are in stars and planets. The scientists who tried to find out what was happening call this part of science "spectroscopy".