Chapter 13 Flashcards
What is apparent brightness?
The brightness of a star as it appears in our sky
What is luminosity?
The total amount of energy radiated by a star per second
What percentage of the time is the spectroscopic parallax accurate?
10%
Which parallax is useful for smaller distances and which one is useful for longer distances?
Trigonometric parallax is useful for smaller distances and Spectroscopic parallax is useful for longer distances
What information can you obtain from stellar spectra?
- Composition from absorption/emission lines
- Motion from Doppler effect
- Temperature from peak wavelength
What is the way an animal’s brain combines the different information from its two eyes to perceive the distances to objects around it?
Stereoscopic vision
What is a parallax?
Its the apparent shift in the position of a nearby object as we move
How is trigonometric parallax used to measure the distance to nearby stars?
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.
Why can the trigonometric parallax technique be used only for nearby stars?
The parallax angle of distant stars is too small, so we can’t accurately measure it
What unit of measurement do Astronomers use to measure the distance to stars and galaxies?
Parsec
How many light years is a parsec?
3.26 light years
What is “parsec” short for?
Parallax arcsecond
What is parsec?
It is the distance to a star with a parallax of 1 arcsecond
What is the equation to find brightness?
Luminosity/ 4πd^2
d = distance
How can we tell the surface temperature of a star?
We can tell by looking at its color
What are spectral types?
The groups that stars are classified under
What was the initial classification of the spectra of different stars based on?
The strength of their hydrogen lines
What is the modern classification of the spectra of different stars based on?
Surface temperature
From hottest to coolest, what is the order of letters for spectral classes?
O, B, A, F, G, K, M
Oh Boy, An F Grade Kills Me
Is B0 or B2 hotter?
B0
What spectral class is the Sun?
G2
Because different spectral lines are formed at different temperatures, what can astronomers use to measure a star’s temperature?
Absorption lines
What is spectroscopic parallax?
Its the distance to a star measured using the spectral type and luminosity class
What are heavy elements?
Any element that is more massive than helium
Which element is found the most in the sun?
Hydrogen
What two things do we use to determine the size of a star?
Luminosity and temperature
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
1/4
Recall that Luminosity = Radius^2 x Temperature ^4
What are binary stars?
A system in which two gravitationally bound stars orbit around their common center of mass
(Think about the teeter totter)
What is the balancing point in a binary system?
The center of mass
What is a visual binary system?
A binary system in which the two stars can be seen individually from Earth
What are eclipsing binary systems?
It is a system where one star passes in front of another star, which blocks the other star’s light
What kind of information can we get from an eclipsing binary system?
The size (and temperature) of the two stars
What are spectroscopic binaries?
They are systems whose spectrums can’t be determined visually
How is the stellar spectra of a spectroscopic binary system determined?
By using spectroscopic studies
What is the Hertzsprung-Russell diagram?
It is the diagram that is used to study stars by comparing their luminosity and their temperature
What is the x-axis on the H-R diagram?
Surface temperature
What is the y-axis of the H-R diagram?
Luminosity
Are hotter stars more towards the left side or the right side of the diagram?
Left
Are the more luminous stars more towards the bottom or the top?
Top
Where are each type of star found on the diagram:
- Giant
- Supergiant
- White dwarf
- Upper right
- Upper left
- Lower left
Draw and label the H-R Diagram
Page 377
The most accurate values for distance are those based on measurements of the parallax of about 100,000 nearby stars made by which satellite?
The Hipparcos satellite
What percentage of stars lie in the main sequence?
90%
What information does the H-R diagram contain?
The stellar evolution, sizes, and masses of stars
What distincts stars in the main sequence to other stars?
They are burning hydrogen and helium in their core
What determines where on the main sequence a star will lie?
It’s mass
What is the mass-luminosity relationship?
It’s the relationship between the luminosity and mass of main sequence stars
Why are massive stars more luminous?
They are hotter, which causes fusion to be faster. A faster fusion makes more energy
List of H-R diagram groups
- Supergiants
- Giants
- White Dwarfs
- Red Dwarfs
- Brown Dwarfs
Why do we need to know the luminosity of a star?
We need it in order to find the distance of a star
What properties does the luminosity depend on?
Radius and temperature
What is the equation in order to find luminosity using radius and temperature?
R^2 x T^4
The composition from absorption/emission lines, the motion from Doppler effect, and the temperature from peak wavelength can all be obtained from what?
The Stellar Spectra
What is a double star?
They are a pair of stars that can only be seen as separate stars through an optical telescope
What is a optical double?
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)
How do you find the mass of a star?
By finding the ratio and sum of masses
What does the H-R in H-R diagram stand for?
Hertzsprung-Russell
Why are massive stars hotter?
They need more thermal pressure to hold themselves up against gravity
