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Learn about planets outside our solar system through Exoplanets and Alien Solar Systems by Tahir Yaqoob, Ph.D., a book in our online store book collection.
The human eye has developed the ability to see best in the type of light given off by the Sun. Our eyes are most sensitive to the colors from yellow through green.
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Visible Light

Visible light is one way energy uses to get around. Light waves are the result of vibrations of electric and magnetic fields, and are thus a form of electromagnetic (EM) radiation. Visible light is just one of many types of EM radiation, and occupies a very small range of the overall electromagnetic spectrum. We can, however, directly sense light with our own eyes, thus elevating the role of this narrow window in the EM spectrum because of its significance to us.

Light waves have wavelengths between about 400 and 700 nanometers (4,000 and 7,000 ). Our eyes perceive different wavelengths of light as the rainbow hues of colors. Red light has relatively long waves, around 700 nm (10-9 meters) long. Blue and purple light have short waves, around 400 nm. Shorter waves vibrate at higher frequencies and have higher energies. Red light has a frequency around 430 terahertz, while blue's fequency is closer to 750 terahertz. Red photons carry about 1.8 electron volts (eV) of energy, while each blue photon transmits about 3.1 eV.

Visible light's neighbors on the EM spectrum are infrared radiation on the one side and ultraviolet radiation on the other. Infrared radiaiton has longer wavelength waves than red light, and thus oscillates at a lower frequency and carries less energy. Ultraviolet radiation has waves with shorter wavelengths than do blue or violet light, and thus oscillates more rapidly and carries more energy per photon than visible light does.

Light travels at the incredible speed of 299,792.458 kilometers per second (about 186,282.4 miles per second). At this amazing speed, light could circle Earth more than seven times in one second! The lowercase letter "c" is often used to represent the speed of light in equations, such as Einstein's famous relation between energy and matter: "E = mc2". All forms of electromagnetic waves, including X-rays and radio waves and all other frequencies across the EM spectrum, also travel at the speed of light. Light travels most rapidly in a vacuum, and moves slightly more slowly in materials like water or glass.

Last modified July 13, 2005 by Randy Russell.

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Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, as well as books on science education!

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA