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Visible Light Waves
Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light.
When white light shines through a prism, the white light is broken apart into the colors of the visible light spectrum. Water vapor in the atmosphere can also break apart wavelengths creating a rainbow.
Each color in a rainbow corresponds to a different wavelength of electromagnetic spectrum.
How do we "see" using Visible Light?
There are two types of color images that can be made from satellite data -
true-color and false-color.
To take true-color images, like this one, the satellite that took it used
sensors to record data about the red, green, and blue visible light waves
that were reflecting off the earth's surface. The data were combined
later on a computer. The result is similar to what our eyes see.
A false-color image is made when the satellite records data about
brightness of the light waves reflecting off the Earth's surface.
These brightnesses are represented by numerical values - and these values
can then be color-coded. It is just like painting by number!
The colors chosen to "paint" the image are
arbitrary, but they can be chosen to either make the object look realistic,
or to help emphasize a particular feature in the image. Astronomers can even
view a region of interest by using software to change the contrast and
brightness on the picture, just like the controls on a TV! Can you see a
difference in the color palettes selected for the two images below? Both images
are of the Crab Nebula, the remains of an exploded star!
Here's another example - the below pictures show the planet Uranus in
true-color (on the left) and false-color (on the right).
The true-color has been processed to show Uranus as human eyes would see it from the vantage point of the Voyager 2 spacecraft, and is a composite of images taken through blue, green and orange filters. The false color and extreme contrast enhancement in the image on the right, brings out subtle details in the polar region of Uranus. The very slight contrasts visible in true color are greatly exaggerated here, making it easier to studying Uranus' cloud structure. Here, Uranus reveals a dark polar hood surrounded by a series of progressively lighter concentric bands. One possible explanation is that a brownish haze or smog, concentrated over the pole, is arranged into bands by zonal motions of the upper atmosphere.
What does Visible Light show us?
It is true that we are blind to many wavelengths of light. This
makes it important to use instruments that can detect
different wavelengths of light to help us to study the Earth and the
Universe. However, since visible light is
the part of the electromagnetic spectrum that our eyes can see, our whole
world is oriented around it. And many instruments that detect visible light
can see father and more clearly than our eyes could alone. That is why we use
satellites to look at the Earth, and telescopes to look at the Sky!
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NASA Official: Ruth Netting
Last Updated: March 27, 2007