Spectroscopy studies light to determine properties of objects by examining colors, reflecting energy states. It is used in chemistry, astronomy, and has many sub-disciplines. X-ray spectroscopy determines elements and chemical bonds. Astronomical spectroscopy observes continuous and discrete spectra to determine composition of celestial bodies. Discrete spectra identify atoms and their energy levels.
Spectroscopy is the study of light as it breaks down into its constituent colors. By examining these different colors, any number of properties of the object under study can be determined, since the colors of light reflect energy states. More technically, spectroscopy examines the interaction between any matter and radiation. It is used to analyze compounds in chemistry, to determine which different elements make up something, and it is also used in astronomy to obtain information on both the composition and velocity of astronomical bodies.
One can divide spectroscopy into many sub-disciplines, depending on what is being measured and how it is being measured. Some major divisions include mass spectrometry, electron spectroscopy, absorption spectroscopy, emission spectroscopy, X-ray spectroscopy, and electromagnetic spectroscopy. However, there are many other types of spectroscopy as well, including those that look at sound as it scatters or at electric fields.
In X-ray spectroscopy, for example, X-rays bombard a substance. When they strike it, the electrons in the inner shells of the atoms are excited and then de-energized, giving off radiation. This radiation comes out at different frequencies, depending on the atom, and there are slight variations depending on the chemical bonds present. This means that the radiation can be examined to determine what elements are present, in what quantities, and what chemical bonds exist.
In astronomy, spectroscopy can be used to determine a wide variety of things about the composition of stars and other celestial bodies. This is because light is a wave and different energies have different wavelengths. These different wavelengths are related to different colors, which can be observed using telescopes. Spectroscopy involves looking at different colors and using what is known about the energies of different processes and elements to build a map of what is happening thousands of millions of light-years away.
There are two main spectra of light that are observed in astronomical spectroscopy: continuous and discrete. A continuous spectrum has a large range of colors that are relatively continuous. A discrete spectrum, on the other hand, has certain peaks of very bright or very dark lines at specific energies. Discrete spectra that have bright peaks are called emission spectra, while those that have dark peaks are called absorption spectra.
Continuous spectra are emitted by things like stars, as well as things on earth like fires, animals, or light bulbs. Because the energy is released across the wavelength spectrum, it appears rather continuous, although there may be peaks and troughs within the spectrum. Not all of this light, of course, is visible to the naked eye—much of it exists in the infrared or ultraviolet range.
Discrete spectra, on the other hand, are usually caused by something happening to a particular atom. This is because, due to some rules of quantum mechanics, electron clouds have a very specific energy, depending on the associated atom. Each individual element has only a handful of energy levels it can have, and nearly all of them are easily identifiable. At the same time, these elements always want to get back to these base energy levels, so if they get excited in any way, they put out the extra energy in the form of light. That light has the exact wavelength you would expect for that atom, allowing astronomers to visualize the peak of light and recognize which atoms are involved, helping to unlock the secrets of the universe’s composition.
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