Figure 3-52The Absorption and Emission of an Hα Photon This schematic diagram of hydrogen’s four lowest allowed orbits shows what happens when a hydrogen atom absorbs or emits an Hα photon, which is red and has a wavelength of 656.3 nm. The spectral lines created by such events are also shown. (a) A photon is absorbed by the electron, causing the electron to transition from orbit n = 2 up to orbit n = 3. (b) A photon is emitted as the electron makes a transition from orbit n = 3 down to orbit n = 2.