| MadSci Network: Astronomy |
Spectroscopy is the technique of analyzing light by separating it into different wavelengths. A prism, which separates visible light into a rainbow of colors, is an example of spectroscopy.
Spectroscopy provides much more information than measuring the total amount of light arriving from an object in space. Indeed, almost all modern astronomy involves spectroscopy one way or another. For example, if we just see how bright a star is in the blue and yellow, we can derive an approximate temperature. If we divide the light very finely in a spectrograph, we can get an accurate temperature, measure how fast it is moving away from us or towards us, determine its composition and magnetic field, how fast it is rotating, and many other aspects.
The main disadvantage is that spectroscopy is much slower and more expensive than just taking a picture of an object. The more finely a spectrograph spreads out the light, the longer it takes to get a good measurement. Most of the time it is worth it, since spectroscopy provides so much more information. Still, the faintest objects in the universe are too faint for spectroscopy. That is one reason why astronomers are always eager to build bigger and bigger telescopes, which gather more light and enable us to take spectra of fainter objects. There is nothing dangerous about doing spectroscopy.
Spectroscopy can be done at any wavelength of light, from X-rays to the ultraviolet to the visible to the infrared to radio.
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