A hydrogen atom that has gained or lost an electron, and thus has an electric charge. The positive hydrogen ion, H⁺, has lost its only electron and therefore consists of a single proton. A nebula containing H⁺ ions is known as an H II region. The negative hydrogen ion, H⁻, has gained a second electron. H⁻ ions are found in the outer layers of stars such as the Sun. Most of the light received from the Sun actually originates from the formation of H⁻ ions.