Describe the principle of hydrostatic equilibrium as it relates to the internal structure of a star.

For the PP chain 0.7% of the mass participating in nuclear fusion is liberated as energy which produces a star's luminosity. Assume that the core of a main sequence star consists of 10% of its total mass. Hence, estimate the lifetime of a star on the main sequence in terms of its luminosity L/L. Give your answer in years. You may use the observed mass-luminosity relation L x M³.5, where M is the star's total mass. Using typical values, calculate estimates for the main sequence lifetime of a KO star and a 05 star. Describe briefly why your estimate might be more accurate for K stars compared to O stars.

The RR Lyrae stars in a globular cluster have apparent magnitudes of 14. Assuming an absolute visual magnitude of 0.5, calculate how far away is the cluster (in parsecs)? (Hint: Use the Magnitude-Distance Formula: ?=10(??−??+55))

What is the relationship between the color of a reflection nebula and the color of the star that illuminates it?