The nucleus of an atom is the region found in the center of the atom. It consists of the protons and neutrons. The nucleus makes up the majority of an atom's mass; the other part making up the atom's mass is the outer electron clouds surrounding the nucleus.
The nucleus was discovered in 1911 by Hans Geiger and Ernest Marsden, under the guidance of Ernest Rutherford. The study of the atomic nucleus is called nuclear physics. This branch of physics covers the composition and forces that bind the atom together. The word nucleus is derived from the Latin word "nucleus," which refers to the kernel found inside a fruit.