H-beta

H-beta (Hβ, or H-β) is the second line in the Balmer series of hydrogen spectral lines (after H-alpha). It has a wavelength of 486.1 nm (in air; 486.3 nm in a vacuum) and its color is cyan (a greenish blue). It is within the visible-light atmospheric window, thus observable from the ground and is the Fraunhofer lines F line. Deuterium's H-beta wavelength is about 0.1 nm shorter. An H-beta filter (or hydrogen-beta filter) is a narrow-bandwidth filter centered on the H-beta wavelength. H-beta is one of the lines used for intensity mapping at various redshifts for cosmology research.