When a substance emits light, it is because an electron "jumps" from one to another, which is closer to the core. An electron energy-stage is quantized. This means that it can only absorb very specific energy levels. When an electron absorbs energy (usually light), "jump" it out in a second shell. One must have an energy-stage. When an atom is in such a state is called excited or estimated. This condition is not natural for the atom to be using more energy to maintain the electron is in a higher energy stage. Therefore "fall" electron back again after some time during the emission of energy (usually light). The energy emitted by the emissions are merged the same, which is absorbed.
You send light from a chemical element through a lattice, the waves will be deflected, and you will see some obvious points. Depending on the element will be different colors. Sodium emits only one wavelength, while the mercury emits six. The distinct lines are where there is constructive interference. For there is constructive interference, the waves have shifted a whole wavelength.
Light rays do not have the same wavelength. Whether the electron takes the detour or the direct route, it sends out totally the same amount of energy. The energy can be absorbed by the outermost electron and the energy released when the electron falls back, is attached to the element. One each element emits its own light colors or frequencies. This frequency or wavelength can be measured both by hand or using a computer. Some elements emit light mixed with several different frequencies. Here one can measure afbøjningsvinklen of all different frequencies.
Mercury is an example of such an element. It emits light with six different frequencies. If you make spectral lines, for example, the sun, you will find that they do not fit with one element, but more elements combined. The sun is composed primarily of helium and hydrogen. This is evident in a spectrum of the sun.
In this way one can determine the elemental stars and remove celestial composed. This is useful because it is impossible to obtain samples of stars that are many light years away. In this way the spectral lines are very useful for astronomers and physicists in general.
