1. The problem statement, all variables and given/known data https://dept.astro.lsa.umich.edu/~mmateo/Astr404_W16/WebPage/Assignment_Jan21.pdf [Broken] 2. Relevant equations 3. The attempt at a solution Apologize for the long question. I was able to solve problem a and b. But for problem c, I was confused. I asked my professor and he gave me this explanation: "I give you theta (the temperature) as a function of xi; as I recall, that solution is theta = sin(xi) / xi. And you know too that rho(xi) = rho_c * theta since n=1 for this case. So now you calculate the interior mass by replacing rho(r) with with this expression for rho(xi) and r^2 with xi^2 and dr with dxi. Then integrate from 0 (the center) to values between 0 and pi (3.14159 since the surface of the star corresponds to xi=pi). For example, the integral is from 0 to 1 to get m(xi=1) and so forth. As you will see the integral is analytic, so this is just evaluating a simple function for values of xi between 0 and pi. Then you plot this, normalizing the y axis to go from 0 to 1.0 and you can either leave xi to go from 0 to pi, or define a new varlable xi-prime = xi/pi and plot from 0 to 1 using xi-prime. " so I am confused because xi=alpha*r,why can we substitute r^2 with xi^2? Even if we do this, we get a function with a few constants in it. How can we plot this function?