State one difference between

(i)     a main sequence star and a planet.

(ii)     a stellar cluster and a constellation.

State how

(i)     it is known that main sequence stars are made predominantly of hydrogen.

(ii)     a main sequence star remains in equilibrium despite it having a great mass.

The graph shows the variation with wavelength of the intensity of a main sequence star.

Calculate the surface temperature of this star.

(i) stars, and not planets, have cores undergoing fusion;

stars have much greater mass/luminosity/absolute magnitude/temperature than planets;

planets reflect starlight rather than emit;

planets in our solar system can show retrograde motion, stars cannot;

Allow other sensible answers.

(ii) stars in a stellar cluster are close to each other/kept together by gravitation, the stars in a constellation are not;

(i)     the lines in the (absorption) spectrum of the star (correspond to hydrogen wavelengths);

(ii)     the gravitational force that tends to collapse the star is balanced by a force due to radiation pressure;

peak wavelength is at 400 (nm); (accept answers in the range of 380 to 420 (nm))

\(T = \left( {\frac{{{\text{2.9}} \times {\text{1}}{{\text{0}}^{ - 3}}}}{{{\text{400}} \times {\text{1}}{{\text{0}}^{ - 9}}}} = } \right){\text{ 7250 (K)}}\); (accept answers in the range of 6900 to 7600 (K))

Award [2] for a bald correct answer.