The American Scholar - Science Frictions
Let It ShinePrint
Light, from the Southwest’s high desert to the surface of Mars
By Priscilla Long
In Taos, New Mexico, in July, the sky morphs its blues as if a painter were at work. One day last summer the sky was lapis lazuli with clouds so white they couldn’t be real. To the north, Pueblo Peak rose jagged and hazy green. This is high desert: sagebrush, ferric red dirt pocked with prairie dog pitfalls. On black asphalt, a pile of sand on a crack crawled with red ants. I stayed at the Sagebrush Inn—thick adobe and old brick walkways—while teaching at the Taos Summer Writers’ Conference. Georgia O’Keeffe painted in one of these rooms. She traveled to Taos for the uncanny quality of the light.
And just what is this light and just what are these colors?
Color is a form of light, and light enters our eyes in waves. Different wavelengths cause us to see different colors. Red arrives in long light waves, blue in short. But the light spectrum is much wider than we can perceive. The shorter the wave the faster it moves and the more energy it carries. Shortest and fastest are gamma rays. Following gamma rays are x-rays; then ultraviolet light; then the visible light spectrum starting with the shorter waves we see as violet and ending with the longer waves we see as red; then, infrared; and finally, radio waves, long and slow. (Yes. Radio waves are light waves. Your radio converts light into sound.) The range from infrared to radio is sometimes referred to as microwaves.
Telescopes work due to the tremendous amount of information that light carries. Any given substance, whether your purple shirt or the red planet Mars, absorbs some wavelengths and reflects others. The reflected light waves give the object color. For example the element iron absorbs shorter wave lengths and reflects longer (red) waves, giving Mars that red look. My lapis lazuli ring absorbs long light waves and reflects shorter ones—blue.
In a vacuum, light travels at the rate of about 186,000 miles per second (at, by definition, the speed of light). But what is light? It’s both a particle (a thing, like a baseball) and a wave (a pattern). Light comes in pieces, called photons. And photons exhibit both wave behavior and particle behavior.
A particle is simple, but what’s a wave? An ocean wave is not water moving. Instead, it is energy moving through water. The energy vibrates the water molecules, which pass the energy to the next water molecules. When you toss a pebble into a pond, the ripples ripple, while the leaf floating on the surface merely bobs up and down. Energy is moving through the water, bobbing the leaf as it passes, different from water passing through.
Light is an electromagnetic wave.
Consider the concept of a field. A field is associated with a force that affects particles. We have gravitational fields, magnetic fields, and electric fields (areas surrounding charged particles such as electrons or protons). Magnetic and electric fields are linked. When charged particles vibrate they create electromagnetic fields, and these fields transport “electromagnetic radiation”—that is to say, light. In the words of my astronomy book, “Light waves are vibrations of both electric and magnetic fields, caused by the motions of charged particles.”
All of which explicates, but fails to capture, the intense blue—both thick and pale—of the Taos sky.