Question

1. when a star is located at the top of the hertzsprung - russell diagram, that means it is ______________. (1 point)

hot in temperature.
a bright star.
a faint star.

1. which element(s) fuse to form new stars? (1 point)

hydrogen
hydrogen and helium
hydrogen, helium, and carbon

1. what causes a star to move off the main sequence? (1 point)

it cools down in temperature.
it becomes too old to be a main sequence star
it uses up all of its hydrogen.

Explanation:

• Question 6: The Hertzsprung - Russell Diagram (H - R Diagram) has luminosity (brightness) on the y - axis. Stars at the top of the H - R Diagram have high luminosity, meaning they are bright stars. Temperature is on the x - axis (hot stars are on the left, cool on the right).
• Question 7: Stars form through the gravitational collapse of clouds of gas and dust. The primary fuel for star formation and the initial fusion process in stars is hydrogen. In the core of a star, hydrogen nuclei fuse (through nuclear fusion) to form helium. But the formation of new stars (from a nebula) mainly starts with the fusion of hydrogen. Helium and carbon fusion occur later in a star's life cycle (for more massive stars, after the hydrogen - burning phase).
• Question 8: Main - sequence stars are in hydrostatic equilibrium, where the inward pull of gravity is balanced by the outward pressure from nuclear fusion (hydrogen fusion in the core). When a star uses up all of its hydrogen fuel in the core, the core contracts (gravity takes over as there is less outward pressure from hydrogen fusion). This change in the core causes the star to move off the main sequence. A star's temperature change (cooling down) is a consequence of moving off the main sequence in some cases, not the cause. And it's not about the star being "too old" in an absolute sense, but rather the depletion of hydrogen fuel.

Answer:

1. a bright star
2. Hydrogen
3. It uses up all of its Hydrogen