Electromagnetic Radiation | Universe Today

Written by Jean Tate

Electromagnetic radiation, or EM radiation, takes its name from electromagnetism; it is self-propagating waves of electric and magnetic fields … the electric field varies as a sine wave, and that creates a magnetic field at right angles to it (in the plane at right angles – perpendicular – to the direction of propagation), also varying as a sine wave, which sustains the varying (oscillating) electric field, which … you get the idea.

"Radiation" is sometimes used to refer to something other than EM radiation; for example, "ionizing radiation" may be alpha particles (helium nuclei) or beta particles (electrons) from a radioactive substance … and it may also be gamma radiation (which is EM radiation!), from the same substance.

Because it's a wave, EM radiation can be described by its wavelength, or frequency; the two are related … the wavelength times the frequency is c, the speed of light.

From shortest to longest wavelength, EM radiation has the following names: gamma, x-ray (these two overlap somewhat), ultraviolet (UV), (visible) light (astronomers call this part optical, or visual EM radiation; it usually includes part of the UV and part of the IR too), infrared (IR), terahertz radiation (which overlaps with the IR and microwaves; it is called 'submillimeter' by astronomers), microwaves, and radio (these last two overlap somewhat too). For more details on this, see the Universe Today's Guide to Space entry Electromagnetic Spectrum.

James Clerk Maxwell developed a concise description of classical electromagnetism (classical because it does not incorporate quantum mechanics; when it is incorporated, EM radiation is described in terms of its constituent photons) that are today called Maxwell's equations (many of the equations were known before Maxwell, and the equations actually exist in several forms, not all of them developed by Maxwell!), in the 1860s. One of the things which follows from these equations is the self-propagation of oscillating electric and magnetic fields (thousands of physics students remember the day when they first grasped the beauty of this solution as one of the most eye-opening of their course), and as the speed of propagation is c, Maxwell concluded that light is EM radiation. Maxwell worked this out in 1873, and Hertz confirmed it in 1887, using radio waves (though the word radio wasn't used for this EM radiation for another decade).

More? Try this SEGway (Science Education Gateway) website.

Because almost all astronomy depends on the detection of EM radiation, nearly every astronomy Universe Today story is about EM radiation! Some particularly interesting ones are New Insights on Magnetars, Black Holes Might Obscure Earliest Times, and Could Ghost-Like Object Found by Chandra Be Another 'Voorwerp'?.

Astronomy Cast has a whole series of episodes on astronomy based on each kind of EM radiation: Radio Astronomy (which also covers microwaves), Submillimeter Astronomy (which covers terahertz radiation), Infrared Astronomy, Optical Astronomy, Ultraviolet Astronomy, X-Ray Astronomy, and Gamma Ray Astronomy.

Filed under: Astronomy

Tags: electromagnetic radiation, electromagnetic spectrum, electromagnetic waves