Use of appropriate relationships to solve problems relating to luminosity, apparent brightness b, distance between the observer and the star, power per unit area, stellar radius, and stellar surface temperature. (Using the assumption that stars behave as black bodies.)
Knowledge that stars are formed in interstellar clouds when gravitational forces overcome thermal pressure, and cause a molecular cloud to contract until the core becomes hot enough to sustain nuclear fusion, which then provides a thermal pressure that balances the gravitational force.
Knowledge of the stages in the proton–proton chain (p–p chain) in stellar fusion reactions which convert hydrogen to helium. One example of a p–p chain is:
Knowledge that Hertzsprung-Russell (H-R) diagrams are a representation of the classification of stars.
Classification of stars and position in Hertzsprung-Russell (H-R) diagrams, including main sequence, giant, supergiant, and white dwarf.
Use of Hertzsprung-Russell (H-R) diagrams to determine stellar properties, including prediction of colour of stars from their position in an H-R diagram.
Knowledge that the fusion of hydrogen occurs in the core of stars in the main sequence of a Hertzsprung-Russell (H-R) diagram.
Knowledge that hydrogen fusion in the core of a star supplies the energy that maintains the star’s outward thermal pressure to balance inward gravitational forces. When the hydrogen in the core becomes depleted, nuclear fusion in the core ceases. The gas surrounding the core, however, will still contain hydrogen. Gravitational forces cause both the core, and the surrounding shell of hydrogen to shrink. In a star like the Sun, the hydrogen shell becomes hot enough for hydrogen fusion in the shell of the star. This leads to an increase in pressure which pushes the surface of the star outwards, causing it to cool. At this stage, the star will be in the giant or supergiant regions of a Hertzspung- Russell (H-R) diagram.
Knowledge that, in a star like the Sun, the core shrinks and will become hot enough for the helium in the core to begin fusion.
Knowledge that the mass of a star determines its lifetime.
Knowledge that every star ultimately becomes a white dwarf, a neutron star or a black hole. The mass of the star determines its eventual fate.