This star will never reach the point where it will fuse Helium. As a star lives out its main sequence lifetime, the composition and structure of the core changes. A star like the Sun began its lifetime with a core of almost pure Hydrogen, but its core today contains a mix of Hydrogen and Helium. Draw a simple diagram of the Sun's core, showing how the Hydrogen and Helium are distributed, then explain why the Hydrogen and Helium are distributed this way. An interstellar cloud is slowly rotating in pressure equilibrium with its surroundings.
Some outside force disturbs the cloud, causing it to compress and begin to collapse.
Below is the spectrum of a star as viewed through two separate interstellar clouds, both along the line of sight to the star. The two clouds have the same composition, but different temperatures. No explanations are required for this problem. If the cool cloud is stationary with respect to the Earth, describe the motion of the warm cloud. Once stars leave the main sequence and begin burning Helium in their cores, their outer appearance changes dramatically.