# Chapter 11: Surveying The Stars

### 51 terms by skylerself

#### Study  only

Flashcards Flashcards

Scatter Scatter

Scatter Scatter

## Create a new folder

surveying the stars

### What is the approximate chemical composition (by mass) with which all stars are born?

three quarters hydrogen, one quarter helium, no more than 2% heavier elements

luminosity

### According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

Its apparent brightness will decrease by a factor of 9.

### Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?

Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity.

### If star A is closer to us than star B, then Star A's parallax angle is _________.

larger than that of Star B

### Ten parsecs is about _________.

32.6 light-years.
(1 parsec=3.26 ly)

Star A

OBAFGKM

G (2)

### Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?

The star is a member of a binary star system

### Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?

spectroscopic binary

### The axes on a Hertzsprung-Russell (H-R) diagram represent _________.

luminosity and surface temperature

its size

### On an H-R diagram, stellar radii _________.

increase diagonally from the lower left to the upper right

### On an H-R diagram, stellar masses _________.

can be determined for main sequence stars but not for other types of stars

### How is the lifetime of a star related to its mass?

More massive stars live much shorter lives than less massive stars. (Small stars are fuel-efficient like a Prius)

### What is the common trait of all main sequence stars?

They generate energy through hydrogen fusion in their core.

### Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?

Earth would be inside the supergiant.

### What is a white dwarf?

the remains of a star that ran out of fuel for nuclear fusion.

### What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?

It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age.

### Things we can observe directly:

spectral type, color apparent brightness, parallax angle.

Spectral type

### 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?

-No interstellar gas or dust absorbs or scatters light between us and the star.

-We have measured the star's apparent brightness.

-We have measured the star's distance

### We can measure a star's mass directly if __________.

it is a member of an eclipsing binary system.

### Which of the following must be true if the star's inferred mass is to be accurate?

-We have determined that the star is a main-sequence star.

-We have measured the star's spectral type.

### Supergiants

the very largest and brightest of all stars

### Stars are classified on the basis of their-

spectral type and luminosity class

### Cepheids are examples of ________.

pulsating variable stars.

GIANTS

### Red giant or supergiant stars:

-very cool but very luminous

-found in the upper right of the H-R diagram

### Main-sequence stars:

-the majority of stars in our galaxy

-The Sun

-very hot and very luminous star

### White Dwarfs:

-not much larger in radius than Earth

-very hot but very dim

### Main-sequence stars during their formation process:

Take longer time forming if lower mass (M)

Take shorter time forming if higher mass (O)

blue star

### The age of stars in a cluster can be determined by

determining the main sequence turnoff point

### What correctly states the relationship between the apparent brightness, luminosity, and distance of a star?

apparent brightness= luminosity/4(3.14159) X (distance)^2

### If the distance between us and a star is doubled, with everything else remaining the same, its luminosity

remains the same, but its apparent brightness is decreased by a factor of four.

### Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

mass they are formed with

luminosity

### Parallax angle

The angle subtended by a star to the line between the Sun and the Earth
(the Earth-star-Sun angle)

### Apparent Magnitude

The brightness a star appears to be from the Earth. The brightest star has a magnitude of 1 and a star 100 times dimmer a magnitude of 6

### Absolute Magnitude (Luminosity)

A star's apparent magnitude if it were placed 10 parsecs from the Earth

### Stefan's Law

The total energy per second emitted by a black body is proportional to its surface area and to absolute temperature to the fourth power

1/p

### Inverse-square law: equation?

apparent brightness= (absolute brightness)/d^2

Visual
Spectroscopic
Eclipsing

Visual

Spectroscopic

Eclipsing

Example: