The Electromagnetic Spectrum header graphic

Visible Light Waves

The visible spectrum from red (at left) to violet (at right).
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.

Image of a rainbow. When white light shines through a prism or through water vapor like this rainbow, the white light is broken apart into the colors of the visible light spectrum.

How do we "see" using Visible Light?

Cones in our eyes are receivers for these tiny visible light waves. The Sun is a natural source for visible light waves and our eyes see the reflection of this sunlight off the objects around us.

The color of an object that we see is the color of light reflected. All other colors are absorbed.

Light bulbs are another source of visible light waves.

Light bulb
This is an photograph taken from the space shuttle of Phoenix, Arizona. Space Shuttle image of Phoenix.D
This is a true-color satellite image of Phoenix, Arizona. Can you see a difference between this image and the photo above it? True-color satellite image D

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.

Here is a false-color image of Phoenix. How does it compare to the true-color and space shuttle images on this page? False-color image of Arizona

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!

Real colors. Rainbow colors

Here's another example - the below pictures show the planet Uranus in true-color (on the left) and false-color (on the right).

True and false-color images of Uranus.

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!

GOES satellite image - visible light. 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.

False color image of Jupiter. 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.