Although you might not think of them in this way, you are in possession of two extraordinary antennas, perfectly tuned to receive a narrow band of electromagnetic radiation. These antennas are not attached to any radio but rather to your brain. They're your eyes, and they receive signals that fall in the range of visible light.

Light, heat, radio transmissions, and medical X-rays may not seem all that similar, yet they are all forms of electromagnetic radiation -- waves moving through space (not just outer space) that have an electric and magnetic component and are delivered by massless particles called photons. The only thing that differentiates one type of electromagnetic radiation from any other is the energy carried by its photons.

There's lots to discover in the electromagnetic spectrum. Here's a tour that begins with radio waves and takes you through microwaves, infrared radiation, light, ultraviolet radiation, and X-rays. The tour ends with gamma rays, the potentially deadly radiation discussed in the program Death Star.