Chapter 15

Question 1

Luminosity

Answer 1

Amount of power a star radiates (energy per second = watts)

Question 2

Apparent Brightness

Answer 2

Amount of starlight that reaches Earth (energy per second per square meter)

Question 3

Area of a Sphere

Answer 3

4pi(radius)^2

Question 4

The relationship between apparent brightness and luminosity depends on distance:

Answer 4

Brightness = Luminosity/4pi(distance)^2

Question 5

We can determine a star’s luminosity if we can measure its distance and apparent brightness:

Answer 5

Luminosity = 4pi(distance)^2 x (brightness)

Question 6

How would the apparent brightness of Alpha Centauri change if it were three times farther away?

Answer 6

It would be only 1/9 as bright

Question 7

Parallax

Answer 7

The apparent shift in position of a nearby object against a background of more distant objects.

Question 8

Most luminous stars

Answer 8

10^6 Lsun

Question 9

Least luminous stars

Answer 9

10^-4 Lsun

Question 10

Thermal Radiation

Answer 10

The energy emitted by an object as a result of its temperature

Question 11

Properties of Thermal Radiation

Answer 11

Hotter objects emit more light per unit area at all frequencies.

Hotter objects emit photons with a higher average energy.

Question 12

Whats the temp of the Hottest Stars?

Answer 12

50,000k

Question 13

What the temp of the Coolest Stars?

Answer 13

3,000 K

Question 14

Whats the temp of the Sun’s surface?

Answer 14

5,800 K

Question 15

Level of ionization also reveals

Answer 15

A star’s temperature

Absorption lines in star’s spectrum tell us its ionization level.

Question 16

Spectral Type

Answer 16

(Hottest) O B A F G K M (Coolest)

Question 17

Which kind of star is hottest?

Answer 17

A star

Question 19

Types of Binary Star Systems

Answer 19

Visual binary
Spectroscopic binary
Eclipsing binary
About half of all stars are in binary systems.

Question 20

Visual Binary

Answer 20

a gravitationally bound binary star system that can be resolved into two stars

Question 21

Spectroscopic Binary

Answer 21

We determine the orbit by measuring Doppler shifts.

Question 22

Eclipsing Binary

Answer 22

We can measure periodic eclipses.
We measure mass using gravity.

Direct mass measurements are possible only for stars in binary star systems.

Question 23

Need Two out of Three Observables to Measure Mass

Answer 23

Orbital period (p)
Orbital separation (a or r = radius)
3. Orbital velocity (v)

Question 24

Most massive stars

Answer 24

100 Msun

Question 25

Least massive stars

Answer 25

0.08 Msun

Question 26

What is a Hertzsprung-Russell Diagram?

Answer 26

An H-R diagram plots the luminosity, temperature, color, spectral type of stars

Question 27

Main Sequence

Answer 27

a series of star types to which most stars belong, are fusing hydrogen into helium in their cores like the Sun.

Question 28

Giants and SuperGiants

Answer 28

They are stars with lower T and higher L than main- sequence stars must have larger radii. larger and redder after exhausting their core hydrogen

Question 29

White Dwarfs

Answer 29

Stars with higher T and lower L than main-sequence stars must have smaller radii. small and white after fusion has ceased

Question 30

A star's full classification includes spectral type (line identities) and luminosity class

Answer 30

I - supergiant II - bright giant III - giant IV - subgiant V - main sequence

Question 31

Luminous main-sequence stars are

Answer 31

Hot (Blue)

Question 32

Less luminous ones are

Answer 32

Cooler (Yellow or Red)

Question 33

The mass of a normal, hydrogen-burning star determines

Answer 33

Luminosity and spectral type

Question 34

Core pressure and temperature of a higher-mass star

Answer 34

Need to be larger in order to balance gravity.

Question 35

Higher core temperature boosts fusion rate leading to

Answer 35

Larger luminosity

Question 36

Luminosity (star)

Answer 36

From brightness and distance

Question 37

Temperature (star)

Answer 37

Room color and spectral type 3000 K–50,000 K

Question 38

Mass (star)

Answer 38

From period (p) and average separation (a) of binary star orbit

Question 39

Sun's life expectancy

Answer 39

10 billion years

Question 40

Life expectancy of 10Msun star

Answer 40

10 times as much fuel, uses it 10^4 times as fast

Question 41

Life expectancy of 0.1MSun star

Answer 41

0.1 times as much fuel, uses it 0.01 times as fast

Question 42

Main-Sequence High-Mass Star

Answer 42

High Luminosity Short-lived Larger Radius Blue

Question 43

Main-Sequence Low-Mass Star

Answer 43

Low luminosity Log-lived Small radius Red

Question 44

Off the Main Sequence

Answer 44

Those that have finished fusing H to He in their cores are no longer on the main sequence

Question 45

Globular cluster

Answer 45

Up to a million or more stars in a dense ball bound together by gravity about 13 billion years old

Question 46

The Pleiades cluster

Answer 46

Now has no stars with life expectancy less than around 100 million years