English: A depiction of the atomic structure of the helium atom. The darkness of the electron cloud corresponds to the line-of-sight integral over the probability function of the 1s atomic orbital of the electron. The magnified nucleus is schematic, showing protons in pink and neutrons in purple. In reality, the nucleus (and the wavefunction of each of the nucleons) is also spherically symmetric and 1s, and the four particles, each with a different quantum number, like the electrons in the helium atom, are all most likely to be found in the same space, at the exact center of the nucleus. (For more complicated nuclei this is not the case.Thanks to Åke Back.)