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http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html |
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You actually know more about it than you may
think! The electromagnetic (EM) spectrum is just a name that scientists
give a bunch of types of radiation when they want to talk about them as a
group. |
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Radiation is energy that travels and spreads out
as it goes-- visible light that comes from a lamp in your house or radio
waves that come from a radio station are two types of electromagnetic
radiation. |
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Other examples of EM radiation are microwaves, infrared
and ultraviolet light, X-rays and gamma-rays. Hotter, more energetic
objects and events create higher energy radiation than cool objects. Only
extremely hot objects or particles moving at very high velocities can
create high-energy radiation like X-rays and gamma-rays. |
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Radio: yes, this is the same kind of energy that
radio stations emit into the air for your boom box to capture and turn into
your favorite Mozart, Madonna, or Coolio tunes. But radio waves are also
emitted by other things ... such as stars and gases in space. You may not
be able to dance to what these objects emit, but you can use it to learn
what they are made of. |
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Microwaves: they will cook your popcorn in just
a few minutes! In space, microwaves are used by astronomers to learn about
the structure of nearby galaxies, including our own Milky Way! |
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Infrared: we often think of this as being the
same thing as 'heat', because it makes our skin feel warm. In space, IR
light maps the dust between stars. |
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yes, this is the part that our eyes see. Visible
radiation is emitted by everything from fireflies to light bulbs to stars
... also by fast-moving particles hitting other particles. |
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we know that the Sun is a source of ultraviolet
(or UV) radiation, because it is the UV rays that cause our skin to burn!
Stars and other "hot" objects in space emit UV radiation. |
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your doctor uses them to look at your bones and
your dentist to look at your teeth. Hot gases in the Universe also emit
X-rays . |
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radioactive materials (some natural and others
made by man in things like nuclear power plants) can emit gamma-rays. Big
particle accelerators that scientists use to help them understand what matter
is made of can sometimes generate gamma-rays. But the biggest gamma-ray
generator of all is the Universe! It makes gamma radiation in all kinds of
ways. |
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We may think that radio waves are completely
different physical objects or events than gamma-rays. They are produced in
very different ways, and we detect them in different ways. But are they
really different things? The answer is 'no'. Radio waves, visible light,
X-rays, and all the other parts of the electromagnetic spectrum are
fundamentally the same thing. They are all electromagnetic radiation. |
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Electromagnetic radiation can be described in
terms of a stream of photons, which are massless particles each traveling
in a wave-like pattern and moving at the speed of light. |
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Each photon contains a certain amount (or
bundle) of energy, and all electromagnetic radiation consists of these
photons. |
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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, microwaves have a little more
energy than radio waves, infrared has still more, then visible,
ultraviolet, X-rays, and ... the most energetic of all ... gamma-rays |
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Actually, the electromagnetic spectrum can be
expressed in terms of energy, wavelength, or frequency. |
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Each way of thinking about the EM spectrum is
related to the others in a precise mathematical way. |
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Notes
