Review

#01

In order to glow, stars convert mass into energy. They have finite mass, so they have finite lifetimes. Low mass stars live longer than high mass stars.

#02

It is the condition of force balance in a fluid combined with no motion of the fluid.

#03

About 10 billion years.

#06

About 0.4 AU.

#09

The core pressure is electron degenerate. In such a state the pressure does not depend on temperature. When He fusion starts, the temperature rises, fusion becomes more rapid, which makes the temperature go up more, and the whole thing becomes unstable and explosive. This is a runaway condition that lasts until conditions change so that the pressure responds to temperature again, and the core expands to regulate itself.

#13

Planetary nebulae are a stage when a star has cast off its outer atmospheric layers. The ring appearance arises because the emitting gas lives in a spherical shell. Near the apparent limb of the shell, there is more emitting gas along the line-of-sight, giving the limb portion a brighter appearance.

#14

White Dwarfs are electron degenerate stars, the remains of a stellar interior. They will exist in this stay growing steadily cooler and fainter with time.

#18

They look for the main sequence turn-off point. This works, assuming that stars were born about the same time.

#19

Roche Lobe is a term in reference to binary stars. A Roche Lobe is a region in which the gas belongs to a given star.