National Aeronautics and Space Administration

If we could see only X-rays, we could see things that either emit X-rays or halt their transmission. Our eyes would be like the X-ray film used in hospitals. When you get an X-ray taken at the hospital, X-ray sensitive film is put on one side of your body, and X-rays are shot through you. Because your bones are dense and absorb more X-rays then your skin does, dark silhouettes of your bones are left on the X-ray film while your skin appears transparent.

When the Sun shines on us at a certain angle, our shadow is projected onto the ground. Similarly, when X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film. To the right is the first X-ray image ever taken. Wilhelm Conrad Roentgen, who discovered X-rays in 1895, took this X-ray of his wife's hand. The shadows of her finger bones and wedding ring are all visible.