In doing so, they give up some of the energy that was imparted by the colliding electron and emit it in the form of the colored lights peculiar to each element. The aurora is produced by a process entirely similar to that which occurs inside laboratory discharge tubes. The pressures are roughly the same, and the electric current for the creation of the aurora is supplied by a continuous flow of electrons from the sun. One problem that Angstrom encountered was trying to identify the element that produced the typically greenish-white light observed in the aurora. It was not until 1925 that two Canadian scientists identified atomic oxygen as being the agent responsible.
Atomic oxygen consists of only one oxygen atom, and is rare in the lower atmosphere.
A complex set of interactions occurs when the electrons from the sun enter the earth's outer atmosphere. This produces an emission in the ultraviolet range which is invisible to the naked eye. The ejected electron and the one that knocked it out of the nitrogen molecule then travel further down into the atmosphere, bumping into more atoms and molecules as they go. Thus the aurora appears brighter near its lower border at an altitude of around 70 miles as the atmosphere gets denser and the energetic electrons are slowed down and experience more collisions. The greenish-white light observed here is produced primarily by atomic oxygen.