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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.
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 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).
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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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This is a visible light image of Phoenix, Arizona, taken from the GOES satellite. We often use visible light images to see clouds and to help predict the weather. |
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We not only look at the Earth from space but we can also look at other planets from space. This is a visible light image of the planet Jupiter. It is in false color - the colors were chosen to emphasize the cloud structure on this banded planet - Jupiter would not look like this to your eyes. |
