A Radio Wave is not a Gamma-Ray, a Microwave is not an X-ray...
or is it?
We may think that radio waves are completely different physical
objects or events than
They are produced in very different ways, and we detect them in different
ways. But are they really different things? The answer is 'no'.
X-rays, and all the
other parts of the
spectrum are fundamentally the same thing. They are all
Electromagnetic radiation can be described in terms of a stream of massless
particles, each traveling in a wave-like pattern and moving at the
light. Each massless particle contains a certain amount (or bundle) of
energy. Each bundle of energy is called a photon, and all electromagnetic
radiation consists of these photons. The only difference between the various
types of electromagnetic radiation is the amount of energy found in the
photons. Radio waves have photons with low energies,
a little more energy than radio waves,
still more, then visible,
X-rays, and... the most energetic of all... the gamma-rays.
Actually, the electromagnetic spectrum can be expressed in terms of energy,
way of thinking about the EM spectrum is
related to the others in a precise mathematical way. So why have three
ways of describing things arisen, each with a different sets of physical units?
After all, frequency is measured in cycles per second (which is called a
is measured in
meters, and energy
is measured in
The answer is that scientists don't like to use big numbers when they
don't have to. It is much easier to say or write "two
kilometers or 2
km" than "two thousand meters or 2,000 m". So generally,
scientists use whatever units are easiest for whatever they are working with.
astronomers tend to use wavelengths or frequencies. This is
because most of the radio part of the EM spectrum falls in the range from a
about 1 cm to 1 km, and 1 kilohertz (kHz) to 1 megahertz (MHz). The radio is a
very broad part of the EM spectrum. Infrared astronomers also use wavelength
to describe their part of the EM spectrum. They tend to use microns (or
millionths of meters) for wavelengths, so that they can say their part of the
EM spectrum falls in the range 1 to 100 microns. Optical astronomers use
wavelengths as well. In the older "CGS" version of the metric
system, the units used were angstroms. An angstrom is equal to 0.0000000001
meters (10-10 m in
notation)! In the newer
of the metric system, we think of visible
light in units of
nanometers or 0.000000001 meters (10-9 m). Then we have the
violet, blue, green, yellow, orange, and red light we know so well having
wavelengths between 400 and 700 nanometers. This is a very tiny part of the
EM spectrum. By the time you get to the ultraviolet, X-ray, and gamma-ray
regions of the EM spectrum, lengths have become too tiny to think about any
more. So scientists usually refer to these photons by their energies, which
are measured in the tiny unit of electron volts. Ultraviolet radiation falls
in the range from a few electron volts (eV) to a about 100 eV. X-ray photons
have energies in the range 100 eV to 100,000 eV (or 100 keV). Gamma-rays then
are all the photons with energies greater than 100 keV.