Atomic Spectra There's another neat way to understand what happens when an electron changes its state in an atom and a photon is created or destroyed. When a photon is emitted, it has a definite wavelength. This wavelength can be calculated if you know the difference in the electron's energy after and before the photon comes out. The bigger the energy difference, the shorter the wavelength. In the experiment below, a line appears at the wavelength of the emitted photon when the electron changes its energy (and state) in the Bohr model of the hydrogen atom. That kind of information is called the spectrum of the emitted radiation. Click on an orbit to make the electron jump energy levels. Why is it called a spectrum? I thought a spectrum is what you get when you put a prism in the path of white light. The prism spreads the light out into a rainbow of colors. That's right! We see each of the different wavelength photons in the visible range of radiation as a different color. The lines you see in the spectrum diagram for the hydrogen atom also include radiation at wavelengths that are outside the range of visible colors. What do you think the rainbow spectrum of sunlight looks like if you study it really carefully (with a physicist's spectrometer or grating, for example)? Oh, I get it now; those bands of colors that seem to be continuous are really just a bunch of photon lines packed close together. Right again. They come from changes in the energy states of electrons in atoms in the sun -- including hydrogen and other, heavier atoms. Now I can tell you more about photon emission from heavy atoms, or we can skip to the story of how x-rays are produced in heavy atoms.