Correction: A previous version of this article incorrectly said that the sky is blue because gas molecules in the atmosphere do not absorb the wavelength of light corresponding to the color blue. That wavelength of light is absorbed by atmospheric molecules and then radiated in different directions. As a result, the scattered light is seen coming from everywhere, giving the sky a blue color. This version has been corrected.


(istockphoto)

The recent warm weather has me dreaming of summer and has me longing to visit the farmers market that’s a few blocks from my house. The vendors there sell the most delicious-looking strawberries I have ever seen. Last summer, I popped one in my mouth without washing it. (Sorry, Mom.) The strawberry tasted even better than it looked.

Don’t get nervous — today’s article is not about the benefits of eating fruits and vegetables. Whew! But it is about your senses, the ones that made me appreciate those strawberries.

Humans have five senses: hearing, vision, touch, smell and taste. We have these senses because our nervous system is able to recognize specific physical properties in the world around us.

Sound is a perception certain animals experience when air molecules vibrate, thereby moving their eardrums. When an eardrum moves, nerve impulses from the inner ear are transmitted (sent) to the brain, causing the “sound” to be heard. But, for example, earthworms do not have ears and therefore cannot hear. They can sense vibrations around them, however, which may come in handy if a bird lands outside their burrow, hopping around waiting for breakfast.

There is a famous question that explores the concept of hearing. “If a tree falls in the forest and no one is there to hear it, does it make a sound?” People have been debating this question for hundreds of years. When I was in college, my physics professor said the answer was no. His reasoning went like this:

If a tree falls in a forest and no one is nearby, air molecules vibrate as it crashes to the ground. However, if no eardrums were around to respond to the event, the vibrating air molecules did not create a sound. No eardrums, no sound.

The part of the eye that transmits visual information to the brain is called the retina. The retina has two types of cells that enable this amazing function to occur: rods and cones. Rods process black-and-white images. Cones are responsible for color images.

Of course, this brings up the question: Why do objects have color in the first place? If you’ve ever seen a prism or a rainbow, you know that light can be separated into a fabulous array of colors called the light spectrum. Each color has a different wavelength (size), which is a type of measurement scientists use to describe how things including radio waves, light waves and infrared (heat) waves travel through space.

Which brings me to another famous question Why is the sky blue? People don’t seem to argue about the answer to this question as much as they do about the tree in the forest. As light passes from the sun to the Earth, it is absorbed by molecules in the atmosphere and then radiated in different directions. As a result, the scattered light is seen coming from everywhere, giving the sky a blue color. Of course, the sky isn’t always blue. On cloudy days, it can be gray; at sunset it can be purple, orange and red. That’s because different wavelengths of light are being absorbed and creating a kaleidoscope of color.

Bonus Question Why is a strawberry red? Because when light strikes the strawberry, the fruit absorbs all of the wavelengths of light except red, and that’s what your eye sees.

Howard J. Bennett

Bennett is a Washington pediatrician. Check out his Web site, www.howardjbennett.com, for past KidsPost articles and other cool stuff.