18 (3)

Question 1

the main sequence makes sense. The most massive stars have the most gravity and can thus compress their centers to the greatest degree. This means they are the hottest inside and the best at generating energy from nuclear reactions deep within. As a result, they shine with the greatest luminosity and have the hottest surface temperatures.

Answer 1

R 2

Question 2

What about the other stars on the H–R diagram—the giants and supergiants, and the white dwarfs?

Answer 2

these are what main-sequence stars turn into as they age

Question 3

Because stars spend much less time in these later stages of their lives, we see fewer stars in those regions of the H–R diagram.

Answer 3

R 2

Question 4

The faint, red, main-sequence stars are not the stars of the most extreme densities, however. The ……… …….., at the lower-left corner of the H–R diagram, have densities many times greater still.

Answer 4

white dwarfs

Question 5

The first white dwarf star was detected in 1862. Called ……………, it forms a binary system with ………………., the brightest-appearing star in the sky.

Answer 5

Sirius B / Sirius A