Transcript: The first law of thermodynamics states that energy can change forms, but the total amount of energy in a system is always conserved. This is the familiar statement of the conservation of energy familiar for example in gravitational physics with the situation in an orbit where gravitational potential energy is continually trading off between kinetic energy, but the sum or the total is always constant. It seems as if we get starlight for free from nowhere, but in fact starlight comes from the creation of radiant energy from the binding energy of the atomic nucleus. Essentially stars are fusion factories steadily converting mass into energy according to E = mc2.