The Electromagnetic Spectrum
AUTHOR: Candice Vetter

When we think of the spectrum, we think of the rainbow's gradation from red to violet. That is only the visible light portion of the electromagnetic spectrum. The entire spectrum of EM radiation is much larger than what we can see. But how can radiation like visible light and radio waves be connected with electricity and magnetism?

Electricity and magnetism are two components of the electromagnetic force. An electric current produces a magnetic field. Electric charges and magnetic poles both set up energy fields which exhibit lines of force (hence the much-used force field of early SF). Electric and magnetic fields are always together, at right angles to each other, forming a single electromagnetic field. When an electric field changes its magnetic field also changes, causing the electric field to change in response, which affects the magnetic field, and so on. This oscillation makes the electromagnetic field progress outwards in waves. It radiates in waves moving at 300,000 kilometers per second (186,000 miles per second), which happens to be the speed of light.

Coincidence? Hardly.

Light itself radiates in waves, because light IS electromagnetic radiation. EM radiation moves at the speed of light but has a wide range of frequencies. This means some of the waves are very short and frequent. Some are very long and of low frequency.

All these different frequencies form the EM spectrum. That is the entire spectrum of energy particles that travel in wavelengths from the highest to the lowest. The longer the wavelength, the lower the energy content.

Visible light falls in a very small range (380-760 millimicrons) and covers all the colors we see. Violet has a higher frequency than red. Ultraviolet (meaning higher than violet), which we can't see but can feel the effects of in a sunburn (due to its higher energy content) has a still higher frequency. That is, its wavelength is shorter.

The shorter and more frequent the waves, the more damaging they are. So x-rays (which come after UV) are dangerous. The shortest rays, gamma rays, are very dangerous and can kill in seconds. They're produced in stars and nuclear explosions. (But don't confuse gamma rays, which are EM radiation, with alpha and beta radiation, which are also dangerous, and also produced in nuclear explosions, but are highly charged particles of matter, rather than particles of energy.)

At the red end of the spectrum waves are longer and less frequent. Infrared, which is below red, is invisible to us, but we feel those waves as heat. Beyond infrared we have radio waves.

Radio waves range in length from a few millimeters (microwaves) through short wave radio and standard radio, all the way to waves that are kilometers long. These long waves are what are detected by radio telescopes. Which work on the same general principle as visible light telescopes, except they use a radio receiver instead of a lens.


Which shows that light and radio waves are part of the same spectrum, just at different wavelengths. For a real-universe type of proof consider this. Huge jets of energy shot out from the centers of some massive galaxies were never known to exist until x-ray and radio telescopes were built and could detect them. There are stars that barely shine in the visible light but are high in infrared, like a dark hot piece of charcoal (only really, really big).

There are pulsars that only flash their spinning beacons in x-ray. And space is flooded with gamma rays produced by stars.

More discoveries are made with radio telescopes than standard telescopes. We can hear solar flares as static on the radio.

So when your space-faring heroes go beyond our solar system (assuming the problem of faster-than-light travel is solved) they'll need more than a view screen to look through.

Candice Vetter is an amateur astronomer, writer, and event planner (the latter being what keeps food in cupboard), who thinks science is beautiful and not hard to learn.