Visualisation of the structure of the proton. The proton is a constituent of all atomic nuclei. It is made of three quarks (called valence quarks), two up quarks and one down quark. The quarks are held together by the strong nuclear force, seen as the exchange of gluons (straight lines). The three valence quarks are hidden in the corners of a triangular cloud of virtual quarks, anti quarks and gluons which are spontaneously created within the proton. All of these contribute to the interaction between the proton and its neighbours in the nucleus. The colours represent the strong force charges: red, green and blue for particles; cyan, magenta and yellow for antiparticles.