Most astronomical phenomena emit at least some infrared light. Nevertheless, some wavelengths are better suited for studying certain objects than others. Thermal infrared radiation measures relatively cool astronomical phenomena, corresponding roughly to room temperature or lower. These phenomena include planets, comets, and dust in the interstellar medium of galaxies. Infrared light is useful for examining dusty regions that have been warmed by newborn stars, and for studying discarded shells of matter from dying stars.
Most interstellar dust is made of silicates, the same molecular materials as sand.
Some smaller interstellar dust particles are carbon-based molecules. The silicate dust particles absorb ultraviolet and visible light emitted by nearby stars and re-radiates the light as infrared radiation. Many of the fundamental mysteries of astronomy are best studied in the infrared. Hence, IR observations can probe the Universe as it was when it was only a fraction of its present age. Dust is a very effective absorber and re-radiator of optical and ultraviolet light.