page_title: Astronomical spectroscopy
section_title: Background
hierarchical_section_title: Astronomical spectroscopy / Background
context_page_description: Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the spectrum of electromagnetic radiation, including visible light and radio, which radiates from stars and other celestial objects. A stellar spectrum can reveal many properties of stars, such as their chemical composition, temperature, density, mass, distance, luminosity, and relative motion using Doppler shift measurements. Spectroscopy is also used to study the physical properties of many other types of celestial objects such as planets, nebulae, galaxies, and active galactic nuclei.
context_section_description: Astronomical spectroscopy is used to measure three major bands of radiation: visible spectrum, radio, and X-ray.  While all spectroscopy looks at specific areas of the spectrum, different methods are required to acquire the signal depending on the frequency.  Ozone (O₃) and molecular oxygen (O₂) absorb light with wavelengths under 300 nm, meaning that X-ray and ultraviolet spectroscopy require the use of a satellite telescope or rocket mounted detectors.  Radio signals have much longer wavelengths than optical signals, and require the use of antennas or radio dishes. Infrared light is absorbed by atmospheric water and carbon dioxide, so while the equipment is similar to that used in optical spectroscopy, satellites are required to record much of the infrared spectrum.
caption: Electromagnetic transmittance, or opacity, of the Earth's atmosphere