Johannes (Janne) Robert Rydberg (Swedish: [ˈrŷːdbærj]; 8 November 1854 – 28 December 1919) was a Swedish physicist known for devising the Rydberg formula, in 1888, which is used to describe the wavelengths of photons (of visible light and other electromagnetic radiation) emitted by changes in the energy level of an electron in a hydrogen atom.
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