1. a** Outline what is meant by *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 *main sequence*.
4. d** Indicate where you would expect to find the following stars:
- i** Our Sun, T=5700 K
- ii** Vega, T=9600 K
- iii** Betelgeuse, a red supergiant of T=3500 K
- iv** Sirius B, a white dwarf of T=25000 K