Chemical Compositions
Analyzing the composition of interstellar clouds is achieved by studying electromagnetic radiation that we receive from them. Large radio telescopes scan the intensity in the sky of particular frequencies of electromagnetic radiation which are characteristic of certain molecules' spectra. Some interstellar clouds are cold and tend to give out EM radiation of large wavelengths. We can produce a map of the abundance of these molecules to produce an understanding of the varying composition of the clouds. In hot clouds, there are often ions of many elements, whose spectra can be seen in visible and ultraviolet light.
Radio telescopes can also scan over the frequencies from one point in the map, recording the intensities of each type of molecule. Peaks of frequencies mean that an abundance of that molecule or atom is present in the cloud. The height of the peak is proportional to the relative percentage that it makes up.
Read more about this topic: High Velocity Clouds
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