4 a) A blue star will always be hotter than the red star, independent of relative radius of the stars, because the stars have the same radius, the blue star would be more luminous than red star, since the Stefan-Boltzmann law says hotter stars will emit more radiation per unit surface area than cooler stars.

b) If a reddish and a bluish star have the same luminosity, then the reddish star must be larger than bluish star. This again due to the Stefan-Boltzmann law; since the cooler, red star must have more surface area than hot blue star to produce the same luminosity.

8 a) Because it is luminous but cool. The star in the upper right corner of the diagram will be the largest.

b) Because it has the lowest luminosity. But is also hottest, the star in the lower left corner of the diagram would be the smallest.

c) The star in the lower right corner of the diagram would be both small and cool.

d) The star in the upper left corner of the diagram would be large and hot.

e) The stars in the upper left and lower right corner of the diagram would be on the main sequence.

f) The stars in the upper right and upper left corners would have the highest luminosity , and thus be visible to the greatest distance.

Chpt 13

9 a) Stars with masses from 0.1 solar mass to few times the mass of the sun will eventually become white drawfs.

b) Stars with mass in the range of few to roughly 10 solar masses will become neutron stars.

c) Stars with masses greater than roughly 10 solar masses will eventaully become black holes. The sun would eventually become a white drawf.

10. A B3 star has about 10 times the mass of the sun, but few thousand times the luminosity. Thus, it will take such a star roughly 10/few thousand = 1/few hundred as much time as the sun to exhaust its fuel.

8. The main sequence of the open cluster will extend too much brighter stars than globular cluster. The H-R diagram for the open cluster may have red super-giants, while globular cluster would have red gaints.