Spectrometers are used in spectroscopic analysis to identify materials. Spectroscopes are used often in astronomy and some branches of chemistry. Early spectroscopes were simply a prism with graduations marking wavelengths of light. Modern spectroscopes, such as monochromators, generally use a diffraction grating, a movable slit, and some kind of photodetector, all automated and controlled by a computer. The spectroscope was invented by Gustav Robert Georg Kirchhoff and Robert Wilhelm Bunsen.