This page contains a Flash digital edition of a book.
bigger than its brain. Tat’s true. Pigeons have better color vision than most animals on Earth. Tat’s also true. Most hamsters only blink one eye at a time. True. Dolphins can move each eye independently and can process two different images at once. True again. Geckos can see colors about 350 times better than a human can, even in dim lighting. Also true! Animals depend on their eyes. Eyes help


True


animals make sense of the world around them. Animal eyes come in many shapes, sizes, colors, and even quantities. Yet they all do the same job. Tey all catch light. With help from the brain, eyes turn light into sight. A person’s eyes work in the same way.


A person’s sense of sight is one of the most important senses in the body. Sight provides an estimated two-thirds of all the information a human brain takes in. Te eye is oſten compared to a camera. Both


an eye and a camera have a lens that brings an image into focus. Both have lens openings that can adjust to different levels of light. Te eye transmits a constant stream of images to the brain by electrical signals, just as a camera stores images. Te eye, however, is more complicated than a camera. And the eye can see nothing without the help of light.


EYES IN ACTION


From the outside in, eyes are built to turn light into sight. Take a closer look at the human eye. The cornea, iris, pupil, and lens work together to catch and focus light. They send light to the retina in the back of the eye. The retina sends the information to the brain, which interprets what the eye sees.


18 NATIONAL GEOGRAPHIC EXPLORER pupil


or false? An ostrich’s eye is


The Rules of Light Light is a form of energy, such as heat or sound. It can come from natural sources, such as the sun, or artificial sources, such as a lamp. Light is super speedy. In fact, it’s the fastest


known thing in the universe. It travels in waves and nearly straight lines. Light can travel 299,800 kilometers per


second. It zips from the sun to Earth in just over eight minutes! Light doesn’t always travel so fast, though. Water or glass can slow it down, but just a bit. Light may seem hard to explain. Yet, there


are some rules that light always follows. Light reflects, or bounces off objects. It also


refracts, or bends. And it can be absorbed, or soaked up, by objects. Tese rules of light affect what, and how, the eye sees. For example, objects that absorb all the light


rays appear black. Tose that reflect all the rays appear white. Colored objects absorb some and reflect others.


iris iris


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24