The CNO cycle (Carbon Nitrogen Oxygen cycle) is a process carried out in the cores of stars in which four hydrogen nuclei are fused into one helium nucleus with the production of nitrogen and oxygen as intermediate products of the reaction. 12 C acts as an initiating catalyst for the reaction. Within a star, the CNO cycle becomes the dominant energy source once the temperature of the core exceeds about 16 million degrees Kelvin and is the main source of energy for stars with masses greater than about 1.1 solar masses where such temperatures are common. Stars the size of the Sun or smaller are unable to generate the core temperatures required to drive the CNO cycle and at these lower temperatures the proton-proton (p-p) fusion chain predominates. In the Sun, about 10% of the energy comes from the CNO cycle. In both processes 0.7% of the total mass is converted...