It sways our moods and grows our foods. A ubiquitous and enigmatic form of energy, light now shines as the tool of the future.
Get a taste of what awaits you in print from this compelling excerpt.
What we call light is really the same thingin a different set of wavelengthsas the radiation that we call radio waves or gamma rays or x-rays. But in practice scientists often use the term light to mean the portion of the electromagnetic spectrum in the vicinity of visible light. Visible light is unlike any other fundamental element of the universe: It directly, regularly, and dramatically interacts with our senses.
Our eyes each have about 125 million rods and conesspecialized cells so sensitive that some can detect a mere handful of photons. About one-fifth of your brain does nothing but try to deal with the visual world around you, says Sidney Perkowitz. The position of the eyes, semiprotected in the case of the skull close to the brain, is testament to the importance of visual data.
Light offers high-resolution information across great distances (you cant hear or smell the moons of Jupiter or the Crab Nebula). So much information is carried by visible light that almost everything from a fly to an octopus has a way to capture itan eye, eyes, or something similar.
Its worth noting that our eyes are designed to detect the kind of light that is radiated in abundance by the particular starthe sunthat gives life to our planet. Visible light is powerful stuff, moving at relatively short wavelengths, which makes it biologically convenient. To see long, stretched-out radio waves, wed have to have huge eyes, like satellite dishes. Not worth the trouble! Nor would it make sense for our eyes to detect light in the near infrared (though some deep-sea shrimp near hot vents do see this way). Wed be constantly distracted, because any heat-emitting object glows in those wavelengths. If we were seeing infrared, physicist Charles Townes told me one day, all of this room would be glowing. The eye itself is infraredits warm. We dont want to detect all of that stuff.
There is also darkness in the daytime—shadows. There are many kinds of shadows, more than you probably realize—certainly more than I realized until I consulted the shadow expert. I found him at the end of a long and winding drive through Topanga Canyon, just up the coast from Santa Monica, California. David Lynch is an astronomer. Hes also the co-author of a book called Color and Light in Nature, in which I discovered something about shadows that Id never thought of before. Lynch points out that a shadow is filled with light reflected from the sky—otherwise it would be completely black. Black is the way shadows on the moon looked to the Apollo astronauts, because the moon has no atmosphere and thus no sky to bounce light into the unlit crannies of the lunar surface. Only the faint glow of earthshine filled the shadowy recesses.
David Lynch is an astronomer. Hes also the co-author of a book called Color and Light in Nature, in which I discovered something
about shadows that Id never thought of before. Lynch points out that a shadow is filled with light reflected from the skyotherwise it would be completely black. Black is the way shadows on the moon looked to the Apollo astronauts, because the moon has no atmosphere and thus no sky to bounce light into the unlit crannies of the lunar surface. Only the faint glow of earthshine filled the shadowy recesses.
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Natures engineering and engineering natureintriguing choices for desktop wallpaper.
In More to Explore the National Geographic magazine team shares some of its best sources and other information. Special thanks to the Research Division.
Did you know that light is now used to define the length of a meter? In 1983 the International Bureau of Weights and Measures (the organization that presides over the metric system) defined the meter as the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. If that number looks familiar, its because the speed of light in a vacuum is 299,792,458 meters per second.
The standard for the meter was not always based on light. The first determination of the meter took place soon after the French Revolution in the 1790s when a platinum bar equal to one ten-millionth of the distance from the Equator to the North Pole represented the standard meter. In 1889 a more accurate prototype was made of platinum-iridium and was not replaced until 1960 when a measurement of electromagnetic radiation replaced an object as the basis for the meter. In 1960 the definition of a meter was determined by a wavelength of
krypton-86 radiation. In 1983 todays standard was instituted based on visible light (the small slice of the electromagnetic spectrum that we can seewavelengths between 400 and 750 nanometers).
Joe McNally Photography
View more of Joe McNallys photographs in a portfolio of his editorial work which includes conceptual and creative portraiture of some well-known personalities.
Sketches of a History of Classical Electromagnetism
A time line of the history of optics, magnetism, electricity, and electromagnetism with links to biographies of the scientists who studied light from Euclid to Einstein.
Galileo and Einstein
Want to learn how the speed of light was determined and why it appears that light slows down as it approaches that limit? Check out Michael Fowlers lectures on Galileo and Einstein. For lectures specifically on light, start with Lecture 18: The Speed of Light.