1. (a) State what is meant by the following two terms:
- i** The luminosity of a star
- ii The apparent brightness of a star
2. (b) The apparent brightness of the Sun is about 1.3 kWm−2 , and its luminosity is 3.8×1026 W . Calculate how far the Sun is from the Earth.
3. (c) Another main sequence star has the same luminosity as the Sun, but its surface temperature is half that of the Sun. Determine the ratio of the radii of the two stars, rstarr⊙ .