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.
Therefore, much of the radiant energy in the Universe is found in the infrared. The only way to peer into the obscured cocoons of star formation and into the heart of dusty galaxies is through infrared eyes. The resulting IR spectral features are important diagnostic tools for understanding physical conditions and processes in planetary atmospheres, interstellar clouds, and in distant galaxies.