Chapter 11

Question 1

you know that surface temperature is a stellar property that we infer indirectly. What must we measure directly so that we can infer a star’s surface temperature?

Answer 1

spectral type

Question 2

Which of the following must be true if we are to infer (calculate) a star’s luminosity directly from the inverse square law for light?
We have measured the star’s apparent brightness.
We have measured the star’s spectral type.
No interstellar gas or dust absorbs or scatters light between us and the star.
The star must be a member of a binary system.
We have measured the star’s distance.

Answer 2

We have measured the star’s apparent brightness.
No interstellar gas or dust absorbs or scatters light between us and the star.
We have measured the star’s distance.

Question 3

we can measure a star’s mass directly if __________.

Answer 3

it is a member of an eclipsing binary system

Question 4

Before we can use parallax to measure the distance to a nearby star, we first need to know __________.

Answer 4

The Earth-Sun difference

Question 5

Which of the following is a valid way of demonstrating parallax for yourself?

Answer 5

Hold up your hand in front of your face, and alternately close your left and right eyes.

Question 6

What is the cause of stellar parallax?

Answer 6

Earth’s orbit around the Sun

Question 7

The more distant a star, the __________.

Answer 7

smaller its parallax angle

Question 8

Approximately what is the parallax angle of a star that is 20 light-years away?

Answer 8

.16 arcseconds

Question 9

If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would

Answer 9

get smaller

Question 10

What do we need to measure in order to determine a star’s luminosity?

Answer 10

apparent brightness and distance

Question 11

What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?

Answer 11

the time between eclipses and the average distance between the stars

Question 12

Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.

Answer 12

less luminous, cooler, smaller, and less massive

Question 13

Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

Answer 13

cooler and larger in radius

Question 14

Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

Answer 14

hotter and smaller in radius

Question 15

Which of these stars has the coolest surface temperature?

Answer 15

a K star

Question 16

Which of these stars is the most massive?

Answer 16

a main sequence A star

Question 17

Which of these stars has the longest lifetime?

Answer 17

a main sequence M star