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blackbody radiation; however, other methods of electromagnetic wave generation are known:

Thermal emission from ionized gas: As an ionized gas the electrons are free from the nucleus and thus are in no specific energy level; however, the electrons are accelerated as they come m the vicinity .of other charged particles. These accelerations of electrons cause electromagnetic radiations.

Fig. 4, Synchrotron emission: Free electrons in the arms of a galaxy moving at high speed in a gravity field.

Synchrotron radiation: The first emission which is nonthermal in nature is the synchrotron radiation (Fig- 4). In fact most nonthermal radiation in the universe is produced by this methodSynchrotron radiation occurs whenever high velocity (high energy) electrons are accelerated to near the speed of light by a powerful magnetic field. The energy released by synchrotron mechanism is more intense than that released by thermal emission from ionized gas. As a consequence, this type of radiation is responsible for some of the most powerful sources yet detected.

Spectral lines: As electrons jump from lower to higher or from higher to lower energy levels within the atom, energy is either radiated or absorbed. This energy shows up as spectral lines throughout the electromagnetic spectrum.

Many of the spectral lines fall within the visual portion of the spectrum; however, some elements such as hydrogen are capable of producing spectral lines a considerable distance from visible light.

The most famous spectral line within the radio spectrum is the 1420,3 MHz hydrogen line. This is the spectral line produced by neutral hydrogen.

Evidence of this line is found throughout the universe; it occurs in open space between stars and between galaxies and at various temperature levels.

The above is only a brief survey of the mechanics of electromagnetic wave generation simplified from the book Radio Astronomy by John D. Kraus, Every serious student of the subject should consult Dr, Kraus" book for a more detailed discussion.

This portion of the text of this two-part article series has served to acquaint you with some of the individuals who pioneered radio astronomy as well as some of the technical disciplines involved in the field. Part II of the series will cover details about the radio spectrum of interest and describe basic radio telescope systems.

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