A Self-Guided Tour of the Electromagnetic Spectrum
Can you feel the heat? (Well, imagine that you can.) You're in the infrared section of the electromagnetic spectrum. This part of the spectrum is also called radiant heat.
From people to planets, from incense candles to ice cubes, all objects give off infrared radiation. This radiation comes from the thermal motion of molecules. Naturally, the warmer an object is, the more infrared radiation it emits. An object that absorbs more infrared radiation than it releases becomes warmer.
Not all forms of heat are radiant heat. The heat directly above a fire, for example, comes mainly from air molecules that the fire has heated. The heat from a radiator, on the other hand, emits heat in the form of electromagnetic radiation.
If a radiator were to continue to heat up, the wavelengths of some of its radiation would shorten (become more energetic) and start to become visible light—the radiator would begin to glow red.
Infrared radiation can also be used for communication. Take a remote control, for instance. Within the remote is a light-emitting diode (LED) that sends out infrared light. We can't see this light because our eyes aren't equipped to sense infrared. But a TV or VCR is. When you press a button on the remote, the LED emits a series of flashes that the TV or VCR can "see" and read. Incidentally, a video camera can usually see the infrared light from a remote. Try this at home!
This is the constellation Orion, as viewed in infrared wavelengths. The bright stars that you usually see when you look at Orion are difficult to detect at this wavelength. What you can clearly make out in this image are infrared emissions that come mainly from dust and gas.
Betelgeuse, Orion's brightest star, is in the upper center of this image. The faint ring in the upper right of the image is a supernova remnant.