What is Color?

Light is a wave - a cycling motion like waves in the ocean. But unlike ocean waves, which travel through water, light waves travel 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 ocean waves, can be measured 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