Johannes Rydberg, commonly known as Janne Rydberg, (November 8, 1854 - December 28, 1919), was a Swedish physicist mainly known for devising the Rydberg formula, which is used to predict the wavelengths of photons (of light and other electromagnetic radiation) emitted by changes in the energy level of an electron in an atom.

The physical constant known as the Rydberg constant is named after him. Excited atoms with very high values of the principal quantum number, represented by n in the Rydberg formula, are called Rydberg atoms, and a crater on the moon is also named Rydberg in his honour.

He was active at Lund University for all of his working life.

See also

• Rydberg formula
• Rydberg constant