Laser absorption spectroscopy
Spectroscopy is the analysis of interaction between portion of the electromagnetic spectrum and matter. Spectroscopy involved the visible spectrum of light, but where the gamma, x-ray, and UV spectroscopy also are valuable techniques. It involves in any interaction between light and matter, including absorption, emission, scattering, etc.
Spectroscopy helps astronomers to detect the composition, temperature, density, and motion of an object. Infrared spectroscopy helps in identifying the atoms and molecules in the object. The red shift or blue shift in a spectral line tells how fast the object is receding from Earth or coming toward it