Answer the following about the Hertzsprung–Russell diagram:
(1) (a) Outline what is meant by a Hertzsprung–Russell diagram.
(2) (b) Sketch a Hertzsprung–Russell (HR) diagram, showing an approximate scale for the two axes.
(3) (c) Indicate what is meant by the main sequence.
(4) (d) Indicate where you would expect to find the following stars: (i) the Sun, T=5700K; (ii) Vega, T=9600K; (iii) Betelgeuse, a red supergiant of T=3500K; (iv) Sirius B, a white dwarf of T=25000K.