Objectives: Upon completion of this chapter, you will be able to describe the difference between thermal and
non-thermal radiation and give some examples of each. You will be able to distinguish between
thermal and non-thermal radiation curves. You will be able to describe the significance of the
21-cm hydrogen line in radio astronomy.
If the material in this chapter is unfamiliar to you, do not be discouraged if you don’t understand everything the first time through. Some of these concepts are a little complicated and few non-scientists have much awareness of them. However, having some familiarity with them will make your radio astronomy activities much more interesting and meaningful.
What causes electromagnetic radiation to be emitted at different frequencies? Fortunately for us, these frequency differences, along with a few other properties we can observe, give us a lot of information about the source of the radiation, as well as the media through which it has traveled.
Electromagnetic radiation is produced by either thermal mechanisms or non-thermal mechanisms.
Examples of thermal radiation include
Continuous spectrum emissions related to the temperature of the object or material.
Specific frequency emissions from neutral hydrogen and other atoms and molecules.
Examples of non-thermal mechanisms include
Emissions due to synchrotron radiation.
Amplified emissions due to astrophysical masers.
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