Question: Several of your articles about ALMA refer to millimeter-wavelength signals received by the radio telescope as “light.” I understand that these signals exhibit many of the characteristics of light such as diffraction, but at wavelengths longer than infra-red, is it really correct to refer to them as light, or is this just an oversimplification intended to help the public understand? — Scott
Answer: You are right. We use the term “light” as a generalization of the more correct yet less widely understood “electromagnetic radiation”. The customary definition of “light” is usually applied to wavelengths from 4000 to 7000 Angstroms, or 0.0004 to 0.0007 millimeters, where ALMA operates at wavelengths from about 0.3 to 4 millimeters.