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These are the spectral lines of burning sodium atoms, as measured by a light spectrometer. When heated, sodium atoms always emits spectral lines at the same frequencies; the electromagnetic "barcode" unambiguously demonstrates the presence of the element.
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Spectrometers are also used with non-optical telescopes, including radiotelescopes. Radio spectrometers allow researchers to examine the spectral lines that characterise molecules, such as hydrogen cyanide or HCN,
a molecule commonly found in space.
Unlike sodium gas which is comprised of atoms, HCN and other molecules exhibit spectral lines that fall within the radio portion of the electromagnetic spectrum. The peaks in the radio emissions define the spectral lines of such molecules.
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Molecules, on the other hand, can display spectral lines linked not only to energy changes in their constituent atoms, but also to their molecular motions . For example, HCN produces spectral lines corresponding to changes in how fast it rotates or vibrates. As molecules gain energy, their internal motions or vibrations increase. This energy is released as electromagnetic radiation possessing characteristic spectral lines. As energy is lost, the molecular motions and vibrations slow down.
But what causes the changes in energy associated with spectral lines? A variety of processes operate here. These include collisions between atoms and molecules, their interactions with electromagnetic radiation at different wavelengths, and with different types of charge particles found in space. Such particles are accelerated by powerful electrical and magnetic fields prevalent near some stars, particularly when they are born or dying.
Aside from yielding much information about structure, composition and changes in energy, spectroscopy also reveals the motions relative to Earth of a host of astronomical objects. Stars, galaxies and giant molecular clouds for example. By studying how their spectral lines are shifted by their motions with respect to Earth, scientists can determine not only their characteristic motions but also estimate the forces responsible, particularly gravity.
Finally, since spectral lines reveal the presence of specific atoms and molecules in space, these same components can serve as tracers of the physical conditions in their surroundings, particularly those of temperature, density, and pressure.
All this from barcode? Amazing.
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