What is Color?
The color of a star is related to the color of light that it gives off.
Light is a wave - a cycling motion that travels through empty space. When a star
emits a light wave, the wave can travel across empty space to the Earth, where we
see the star's light.
Light waves, like waves in water, can be described by the distance between two
successive peaks of the wave - a length known as the wavelength. Different
wavelengths of light appear to our eyes as different colors. Shorter wavelengths
appear blue or violet, and longer wavelengths appear red.
The animation at the right shows a schematic drawing of a wave. The white line
represents the wavelength. Move the slider to explore how the color of a beam
of light changes with its wavelength.
The order of colors in light, arranged from shortest wavelength to longest,
is called the visible spectrum of light. The image below shows light's visible spectrum,
which runs from violet to red. You might recognize the spectrum as the order of colors
in a rainbow. The wavelengths of light are marked on the visible spectrum in Angstroms;
1 Angstrom = 10-10 meters.
But light waves can also have wavelengths lower or higher than the wavelengths
in the visible spectrum, and many familiar types of radiation are just light waves
with other wavelengths. Ultraviolet light and x-rays have wavelengths shorter than
violet light, and infrared (heat) and radio waves have wavelengths longer than
red light.
The full range of wavelengths for light is called the "electromagnetic
spectrum." The image and table below show which wavelength ranges in the electromagnetic
spectrum correspond to which types of light.
 |
Type of Light |
Wavelengths |
Radio waves |
> 30 cm |
Microwaves |
1 mm - 30 cm |
Infrared |
700 nm - 1 mm |
Visible light |
350 nm - 700 nm |
Ultraviolet |
10 nm - 350 nm |
X-rays |
0.01 nm - 10 nm |
Gamma rays |
< 0.01 nm |
1 nm = 10-9 m |
| 
