Chapter Questions
In the model shown in Figure $12-2,$ how much of the sun's mass is hotter than $13,000,000 \mathrm{K} ?$
What is the life expectancy of a 16 -solar-mass star? Of a 50 -solar-mass star?
How massive could a star be and still survive for 5 billion years?
If the sun expanded to a radius 100 times its present radius, what would its density be? (Hint: The volume of a sphere is $\frac{4}{3} \pi R^{3}$.)
If a giant star 100 times the diameter of the sun were 1 pc from Earth, what would its angular diameter be? (Hint: Use the small-angle formula, in Chapter $3 . .$
What fraction of the volume of a 5 -solar-mass giant star is occupied by its helium core? (Hints: See Figure 12 -9. The volume of a sphere is $\left.\frac{4}{3} \pi R^{3} .\right)$
If the stars at the turnoff point in a star cluster have masses of about 4 solar masses, how old is the cluster?
If an open cluster contains 500 stars and is 25 pc in diameter, what is the average distance between the stars? (Hints: What share of the volume of the cluster surrounds the average star? The volume of a sphere is $\left.\frac{4}{3} \pi R^{3} .\right)$
Repeat Problem 8 for a typical globular cluster containing a million stars in a sphere 25 pc in diameter.
If a Cepheid variable star has a period of pulsation of 2 days and its period increases by 1 second, how late will it be in reaching maximum light after 1 year? After 10 years? (Hint: How many cycles will it complete in a year?)