The above video about the physics of flame is the most recent in the channel. It’s true to its name in terms of run time, but unfortunately, that also means glossing over one of the most satisfying lessons I ever learned about the science of light and color. What actually happens in a flame (or any incandescence) that makes us able to see it?
Between :16 to :26 the video mentions exciting atoms with energy to get them to produce colored light. Electrons orbit around the nucleus of an atom at different energy levels. Visually I think of moons around a planet at different distances. Except that unlike moons, the electrons can jump to a higher energy level. The introduction of energy as heat makes this happen.
So electrons that were at level 1, say, are now at level 2 because they got a boost from heat energy. When the atom cools off, the electrons drop back down to ground level. In doing so, they emit photons. The distance between levels becomes the wavelength of the light. The distances between levels are also unique to each atom, which means the colors they emit -the emission spectrum- when they’re heated are unique (and identifiable).
Of course, deGrasse Tyson’s real point in that tweet, I think, was to express admiration for the manner and clarity which the information is presented, something I’m suddenly self-conscious about looking back on that last paragraph. Wikipedia is more concise:
When the electrons in the atom are excited, for example by being heated, the additional energy pushes the electrons to higher energy orbitals. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon. The wavelength (or equivalently, frequency) of the photon is determined by the difference in energy between the two states. These emitted photons form the element’s emission spectrum.
The frequencies of light that an atom can emit are dependent on states the electrons can be in. When excited, an electron moves to a higher energy level/orbital. When the electron falls back to its ground level the light is emitted.
If you have a better way to explain it, please share.