Electromagnetic Radiation

Electromagnetic radiation is a self-propagating wave in space with electric and magnetic components. Electromagnetic radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Electromagnetic radiation carries energy and momentum, which may be imparted when it interacts with matter. Electromagnetic radiation with a wavelength between approximately 400 nm and 700 nm is detected by the human eye and perceived as visible light.

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How It Pertains To Astronomy

As the electrons descend to lower energy levels, a spectrum is emitted that represents the jumps between the energy levels of the electrons. This is manifested in the emission spectrum of nebulae. Today, scientists use this phenomenon to observe what elements a certain star is composed of. It is also used in the determination of the distance of a star, using the so-called red shift.

Sources

<http://en.wikipedia.org/wiki/Electromagnetic_radiation>