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Astronomy Midterm #3
Inverse square law-sun's interior
58
Astronomy
Undergraduate 2
11/13/2012

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Term
apparent brightness
Definition
How bright a star appears- affected by its distance from us
-closer stars=larger apparent brightness
-apparent brightness decreases according to distance^2
**Distance and luminosity
Term
Luminosity
Definition
total amount of light the sun emits in all directions [watts]
- greater luminosity=greater apparent brightness
Term
Inverse square law for light
Definition
Specifies the relationship between apparent brightness, distance, and luminosity
b= L/4piD^2
b=apparent brightness
d=distance
L=luminosity
Term
If 2 stars are the same distance away, the star with a higher luminosity will have a _____________ apparent brightness
Definition
higher
Term
If two stars have the same luminosity, the star with the _______ distance will have a larger apparent brightness
Definition
smaller
Term
Why does the apparent brightness of a star not tell us the distance?
Definition
Luminosity
Term
Stellar Parallax
Definition
small shift in the sky that is caused by Earth's orbital motion
Term
A star that has a smaller distance from from us wil have a _______ stellar parallax
Definition
Larger
Term
Formula of relationship between a stars parallax and its distance
Definition
d= 1arcsec*pc/p
d=distance to the star
p=stellar parallax of star
Term
Closest star to Earth
Definition
Proxima Centauri
Term
Can only use stellar parallax method to determine the distances of stars within _____pc because if they are farther away their parallaxes are too small to detect
Definition
100
Term
Electrons charge
Definition
Negative
Term
What holds an atom together
Definition
The opposing charges of the protons and neutrons
Term
Short wavelength of light has _____ of energy
Definition
a lot
Term
The amount of energy that an electron loses determines the __________ of light emitted
Definition
wavelength
Term
If the North Star moves 2x closer how does its luminosity change?
Definition
Does not change.
Term
If the north star moves 2x closer, how will its apparent brightness change?
Definition
It will get 4x larger
Term
What causes a star to have a certain luminosity?
Definition
distance away from us and its apparent brightness
Term
What part of an atom has most of the mass?
Definition
nucleus
Term
What causes specific spectra?
Definition
Different combinations of temperature and density
Term
Emission Spectrum
Definition
Emitted by an object that is hot and low density -> see through it
-Dark with some visible wavelengths of light
- only see specific wavelengths
Term
Continuous spectrum
Definition
-emitted by an object that is hot and high density
-see everything
Term
Blackbody
Definition
an object that emits a continuous spectrum
-emits all wavelengths of light because atoms in the object are so crowded that they affect how nearby atoms emit and absorb light
Term
Absorption spectrum
Definition
2 conditions must be met:
1. must be a blackbody emitting a continuous spectrum
2. blackbody's light must pass through a cooler, low density material
-the cooler, low density material absorbs some of the light passing through it, so the light that we observe is missing some wavelengths
-see continuous spectrum with specific wavelengths missing

Light--> cool gas--> absorption spectrum
Term
The spectrum of the sun
Definition
Continuous
Term
Can you determine the composition of an object if it emits a continuous spectrum?
Definition
NO, there are no spectral lines
Term
Composition of the sun
Definition
73% hydrogen, 25% helium, 2% heavier elements
Term
Why are the sun and the stars different colors?
Definition
Stars are all made of the same material - not based on composition
Term
Is a red star hot or cool?
Definition
cool
Term
If a star's surface temperature is large, then each part of the star emits ______ light, so its luminosity is _________
Definition
1. more
2. large
Term
If two stars have the same surface temp, then the star's ________ determines luminosity
Definition
radius
Term
Which is more luminous, a red star, or a blue star?
Definition
blue star
Term
If two stars have the same parallax what else is true?
Definition
same distance
Term
Wien's Law
Definition
Calculate a star's surface temperature
T= 2.9 * 10^6 knm/max wavelength
Term
Stefan-Boltzmann Law
Definition
Calculate star's radius
L=4piR^2constantT^4
Term
If 2 stars have the same radius, but one star has 2x the surface temp of the other star, then the hotter star will have _____ x the luminosity
Definition
2^4 = 16x ... stefan-boltzmann law
Term
if two stars have the same surface temp, but one star has 2x the radius of the other then the bigger star will have _____x the luminosity
Definition
2^2= 4 ... stephan-boltzmann law
Term
White Dwarfs
Definition
extremely small radii and low surface temp and dim
Term
Echo and Foxtrot have same luminosity. Echo's surface temp is 5x larger than Foxtrots. How do their radii compare?
Definition
Foxtrots's radius is 25x larger than echos sqrt (5^4) =25
Term
Transverse Velocity
Definition
Star's velocity through the sky across our line of sight
Term
radial velocity
Definition
a star's velocity directly toward or away from us
Term
Doppler Effect
Definition
a change in the wavelength of a light wave caused by the motion of the emitting object or the observer
-the star's radial velocity affects the light we receive from it through doppler effect
-stars motion toward or away from the earth affects the light we receive
Term
Redshift
Definition
object moving away (towards red end of spectrum) Increased wavelength
Term
blueshift
Definition
object moving towards us (closer to blue end of spectrum) decreased wavelength
Term
Use doppler effect to determine ___________
Definition
radial velocity
Term
The bigger the shift of the absorption spectrum, the ______ the velocity
Definition
faster
Term
Thermonuclear fusion
Definition
2 nuclei combine to form one heavier nucleus
-Only happens when two protons are moving so quickly that they fuse before they can repel each other
Term
Which gas can fuse at lowest temperatures
Definition
hydrogem
Term
Proton-proton chain
Definition
sequence of fusion reactions that happens in the sun's core
-4 hydrogen nuclei (protons) are needed at the beginning of the chain of reactions
-some mass is released as radiative energy
-4 hydrogen=1 helium
Term
Why does the sun's core have the necessary conditions for fusion?
Definition
- core temp is hot
-core is highly dense= protons are close together
Term
neutrinos
Definition
sub-atomic particles that have no charge and very tiny masses
-pass directly through solid matter
-leave sun during proton-proton chain
Term
helioseismology
Definition
the study of vibrations in the sun
Term
What can the sun's vibrations tell us about the sun?
Definition
Sun's temp and density
Term
sun's core
Definition
-makes up 25% of suns radius
-hottest
-densest
Term
radiation zone
Definition
-50% of sun's radius
-dense enough that light can't travel in a straight line, bounces from particle to particle = can take a wave of light 100,000 years to travel through the radiation zone
Term
convection zone
Definition
25% of suns radius
-heated by light from radiation zone=gas has convection
Term
photosphere
Definition
top of the convection zone
=visible surface of the sun
Term
can we use helioseismology to study other stars?
Definition
no, they are too far away to see vibrations
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