Absorption spectroscopy – Anders Jonas Ångström – Astronomical spectroscopy – Astronomy – Black body – Blazar – Bremsstrahlung – Caesium – Cherenkov radiation – Color – Diffraction – Digital signal processing – Direct-sequence spread spectrum – Dispersion (optics) – Eigenstate – Eigenvalue – Electromagnetic radiation – Electromagnetic spectroscopy – Electromagnetic spectrum – Electromagnetism – Emission line – Emission spectrum – FM broadcasting – Frequency domain – Frequency hopping – Frequency spectrum – Gamma-ray burst – Hamiltonian (quantum mechanics) – History of radio – Hue – Isotope – Light – Optical brightener – Particle in a spherically symmetric potential – Piezoelectricity – Power spectrum – RADAR – Radio frequency – Radio – Radiocommunications Agency – Redshift – SETI – Spectrogram – Spectrometer – Spectroscopy – Spectrum analyzer – Sunyaev–Zel'dovich effect – Supernova – Telecommunication – Timbre – Very high frequency – Visible light – Visible spectrum – White noise