Infrared is a form of light that is invisible to our eyes but which we can feel as heat. Infrared telescopes detect heat associated with star formation inside dark cosmic clouds.

There are many forms of light that we can’t see with just our eyes, from gamma rays emitted by nuclear reactions to radio waves that we use in wireless communications. In the middle of this range is visible light.

Why does infrared light penetrate cosmic dust clouds? Infrared light has a longer wavelength that travels through dust easily, while shorter wavelength visible light is scattered by interstellar dust.

For more on infrared astronomy, including the complete "Infrared Zoo",
visit Cool Cosmos at the SIRTF Science Center.