Illustration Of Absorption Systems (image) National Institutes of Natural Sciences Share Print E-Mail Caption Calibrator sources have flat radio spectra. Molecules in the intervening gas clouds absorb radio waves at specific frequencies determined by the type of molecules. Credit R. Ando (The University of Tokyo), ESO/José Francisco Salgado Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.