1). A star has six times the radius of the Sun (Appendix C) and a temperature of 2000 K. Find its luminosity. Compare that to the actual luminosity of the Sun. Stars have an emissivity of 0.95.

What percentage of the energy we use comes from the sun?   25%   50%      More than 90%     Less than 10%

-According to appendix C: radius of the sun is 7 x 10^8 m

c) Derive the Schwarzschild criterion for the onset of convection in an ideal gas, namely d ln T d ln P 7-1 Y Explain all steps in your derivation, and justify any assumptions that you make. d) In a region of convective instability near the surface of a solar-type star of total mass M, the temperature and pressure are related approximately by the expression P KT5/2. Show that the temperature gradient for an ideal gas in hydrostatic = equilibrium in this convection zone is given by dT dr 2Gm(r)μ 5Rr² Further, assuming that the mass in the convection zone is small compared to M, show that at a depth h measured from the top of the convection zone, the temperature is approximately given by T = Ts + 2GMμ -h₂ 5RR² when his small compared to R, and Ts is the temperature at the top of the convection zone.

Explain why the presence of spectral lines of a given element in the solar spectrum tells you that element is present in the sun, but the absence of the lines would not necessarily mean the element is absent from the sun.