When a star fuses hydrogen into helium, 0.937% of the mass converts to energy. This number determines every star's lifetime, luminosity, and fate. Standard astrophysics treats it as a derived quantity from measured nuclear masses — which are themselves fitted parameters. Pentagon Physics derives it from first principles. The binding energy per nucleon follows the equation b² + b = c, where c is the 600-cell spectral weight per nucleon. This equation has a unique stable fixed point at b = σ = 1/φ. Iron-56 is the element nearest this fixed point. Stars burn toward iron because they are converging toward the axiom's fixed point. The 0.937% efficiency is the energy released per step of that convergence.