At the average density of a star-forming molecular cloud, about 10^6 atoms per cm^3, determine how large a sphere you would need to encompass mass equal to that of the Sun? Enter the radius of this sphere in light-years. (HINTS: 10^6 atoms per cm^3 correspond to a density of 1.77×10^-18 kg/m^3; the mass of the Sun is 2×10^30 kg)