Basic purpose of this lecture is to present on Atomic Nucleus. Two ways to rearrange nuclei and get energy. Fission: produces energy by breaking up massive nuclei like Uranium into less massive nuclei like Barium and Krypton; A-bombs; nuclear reactors needs Uranium 235, Plutonium 238. Problem: no Uranium or Plutonium on the Sun. Fusion: produces energy by combining light nuclei like Hydrogen to make more massive nuclei like Helium.