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Astronomy > Chapter 13 > Flashcards

Chapter 13 Flashcards

1
Q

What is apparent brightness?

A

The brightness of a star as it appears in our sky

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2
Q

What is luminosity?

A

The total amount of energy radiated by a star per second

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3
Q

What percentage of the time is the spectroscopic parallax accurate?

A

10%

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4
Q

Which parallax is useful for smaller distances and which one is useful for longer distances?

A

Trigonometric parallax is useful for smaller distances and Spectroscopic parallax is useful for longer distances

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5
Q

What information can you obtain from stellar spectra?

A
  1. Composition from absorption/emission lines
  2. Motion from Doppler effect
  3. Temperature from peak wavelength
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6
Q

What is the way an animal’s brain combines the different information from its two eyes to perceive the distances to objects around it?

A

Stereoscopic vision

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7
Q

What is a parallax?

A

Its the apparent shift in the position of a nearby object as we move

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8
Q

How is trigonometric parallax used to measure the distance to nearby stars?

A

As the Earth moves around the Sun, the apparent positions of nearby stars changes more than the apparent positions of more distant stars. We can determine the distance using the amount of this apparent shift and geometry.

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9
Q

Why can the trigonometric parallax technique be used only for nearby stars?

A

The parallax angle of distant stars is too small, so we can’t accurately measure it

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10
Q

What unit of measurement do Astronomers use to measure the distance to stars and galaxies?

A

Parsec

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11
Q

How many light years is a parsec?

A

3.26 light years

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12
Q

What is “parsec” short for?

A

Parallax arcsecond

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13
Q

What is parsec?

A

It is the distance to a star with a parallax of 1 arcsecond

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14
Q

What is the equation to find brightness?

A

Luminosity/ 4πd^2

d = distance

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15
Q

How can we tell the surface temperature of a star?

A

We can tell by looking at its color

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16
Q

What are spectral types?

A

The groups that stars are classified under

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17
Q

What was the initial classification of the spectra of different stars based on?

A

The strength of their hydrogen lines

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18
Q

What is the modern classification of the spectra of different stars based on?

A

Surface temperature

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19
Q

From hottest to coolest, what is the order of letters for spectral classes?

A

O, B, A, F, G, K, M

Oh Boy, An F Grade Kills Me

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20
Q

Is B0 or B2 hotter?

A

B0

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21
Q

What spectral class is the Sun?

A

G2

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22
Q

Because different spectral lines are formed at different temperatures, what can astronomers use to measure a star’s temperature?

A

Absorption lines

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23
Q

What is spectroscopic parallax?

A

Its the distance to a star measured using the spectral type and luminosity class

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24
Q

What are heavy elements?

A

Any element that is more massive than helium

25
Q

Which element is found the most in the sun?

A

Hydrogen

26
Q

What two things do we use to determine the size of a star?

A

Luminosity and temperature

27
Q 
If star A has twice the surface temperature of the Sun but has the same luminosity as the Sun, the diameter of star A must be \_\_\_\_\_\_\_  the diameter of the Sun:
A. 16 times
B. 4 times
C. 1/2
D. 1/4
A

1/4

Recall that Luminosity = Radius^2 x Temperature ^4

28
Q

What are binary stars?

A

A system in which two gravitationally bound stars orbit around their common center of mass
(Think about the teeter totter)

29
Q

What is the balancing point in a binary system?

A

The center of mass

30
Q

What is a visual binary system?

A

A binary system in which the two stars can be seen individually from Earth

31
Q

What are eclipsing binary systems?

A

It is a system where one star passes in front of another star, which blocks the other star’s light

32
Q

What kind of information can we get from an eclipsing binary system?

A

The size (and temperature) of the two stars

33
Q

What are spectroscopic binaries?

A

They are systems whose spectrums can’t be determined visually

34
Q

How is the stellar spectra of a spectroscopic binary system determined?

A

By using spectroscopic studies

35
Q

What is the Hertzsprung-Russell diagram?

A

It is the diagram that is used to study stars by comparing their luminosity and their temperature

36
Q

What is the x-axis on the H-R diagram?

A

Surface temperature

37
Q

What is the y-axis of the H-R diagram?

A

Luminosity

38
Q

Are hotter stars more towards the left side or the right side of the diagram?

A

Left

39
Q

Are the more luminous stars more towards the bottom or the top?

A

Top

40
Q

Where are each type of star found on the diagram:

  1. Giant
  2. Supergiant
  3. White dwarf
A
  1. Upper right
  2. Upper left
  3. Lower left
41
Q

Draw and label the H-R Diagram

A

Page 377

42
Q

The most accurate values for distance are those based on measurements of the parallax of about 100,000 nearby stars made by which satellite?

A

The Hipparcos satellite

43
Q

What percentage of stars lie in the main sequence?

A

90%

44
Q

What information does the H-R diagram contain?

A

The stellar evolution, sizes, and masses of stars

45
Q

What distincts stars in the main sequence to other stars?

A

They are burning hydrogen and helium in their core

46
Q

What determines where on the main sequence a star will lie?

A

It’s mass

47
Q

What is the mass-luminosity relationship?

A

It’s the relationship between the luminosity and mass of main sequence stars

48
Q

Why are massive stars more luminous?

A

They are hotter, which causes fusion to be faster. A faster fusion makes more energy

49
Q

List of H-R diagram groups

A
  1. Supergiants
  2. Giants
  3. White Dwarfs
  4. Red Dwarfs
  5. Brown Dwarfs
50
Q

Why do we need to know the luminosity of a star?

A

We need it in order to find the distance of a star

51
Q

What properties does the luminosity depend on?

A

Radius and temperature

52
Q

What is the equation in order to find luminosity using radius and temperature?

A

R^2 x T^4

53
Q

The composition from absorption/emission lines, the motion from Doppler effect, and the temperature from peak wavelength can all be obtained from what?

A

The Stellar Spectra

54
Q

What is a double star?

A

They are a pair of stars that can only be seen as separate stars through an optical telescope

55
Q

What is a optical double?

A

A chance alignment of two stars that appear to be close to one another, but they actually lie at different distances and aren’t gravitationally bound
(An optical illusion)

56
Q

How do you find the mass of a star?

A

By finding the ratio and sum of masses

57
Q

What does the H-R in H-R diagram stand for?

A

Hertzsprung-Russell

58
Q

Why are massive stars hotter?

A

They need more thermal pressure to hold themselves up against gravity

Astronomy (10 decks)

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