Objectives: When you have completed this chapter, you will be able to describe several important variables in the media through which the radiation passes and how they affect the particles/waves arriving at the telescope. You will be able to describe atmospheric “windows” and give an example. You will be able to describe the effects of absorbing and dispersing media on wave propagation. You will be able to describe Kirchhoff’s laws of spectral analysis, and give examples of sources of spectral lines. You will be able to define reflection, refraction, scintillation, and Faraday rotation.
Electromagnetic radiation from space comes in all the wavelengths of the spectrum, from gamma rays to radio waves. However, the radiation that actually reaches us is greatly affected by the media through which it has passed. The atoms and molecules of the medium may absorb some wavelengths, scatter (reflect) other wavelengths, and let some pass through only slightly bent (refracted).
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