<P> The emission spectrum of atomic hydrogen is divided into a number of spectral series, with wavelengths given by the Rydberg formula . These observed spectral lines are due to the electron making transitions between two energy levels in an atom . The classification of the series by the Rydberg formula was important in the development of quantum mechanics . The spectral series are important in astronomical spectroscopy for detecting the presence of hydrogen and calculating red shifts . </P> <P> To a good approximation, a hydrogen atom can be thought of as consisting of an electron orbiting its nucleus . The electromagnetic force between the electron and the nuclear proton leads to a set of quantum states for the electron, each with its own energy . These states were visualized by the Bohr model of the hydrogen atom as being distinct orbits around the nucleus . Each energy state, or orbit, is designated by an integer, n as shown in the figure . </P> <P> Spectral emission occurs when an electron transitions, or jumps, from a higher energy state to a lower energy state . To distinguish the two states, the lower energy state is commonly designated as n ′, and the higher energy state is designated as n . The energy of an emitted photon corresponds to the energy difference between the two states . Because the energy of each state is fixed, the energy difference between them is fixed, and the transition will always produce a photon with the same energy . </P>

What is the longest wavelength line in the paschen series for hydrogen