The Sun and other stars Flashcards
How can we determine what elements are present in the solar atmosphere?
With a star’s absorption line spectrum
How does the composition of earth compare to the composition of the Sun?
Earth contains the same elements as the Sun but in different proportions
State of matter of the sun
Plasma (hot ionized gas) because it’s so hot that many atoms are stripped of electrons. This also means that there are many free electrons in the sun.
Layers of the Sun beneath the Visible Surface
corona, chromosphere, photosphere, convection zone, radiative zone, core.
Layer of the sun that is the source of all energy
core
Layer of the sun that is the hottest
core
Layer of the sun above the core
radiative zone
Describe the movement of the light transported through the radiative zone
slowly (because of the high density a photon continuously hits matter which causes it to change direction and lose energy)
Outermost layer of the sun
convection zone
Purpose of the convection zone
transports energy from the edge of thee radiative zone to the surface through giant convection cells/, similar to a pot of boiling oatmeal.
Which layer of the sun is visible
photosphere
What is the structure of the photosphere
Granulation
Appearance of Granules
appear as bright area surrounded by narrow, darker (cooler) regions
Lifetime for a granule
5 to 10 min
Why are the outer layers of the sun difficult to observe
- because they are transparent to most visible radiation and emit only a small amount of light
Which is hotter, the chromosphere or the photosphere
chromosphere
Hottest part of the solar atmosphere
corona
Part of the sun where the rapid temperature rise occurs
transition region
Outermost part of the sun
Corona
Why don’t we see the light of the corona until an ecclipse
Because of the intense light of the photosphere
Corona
- outermost part of the sun
- low density
Solar Wind
- stream of charged particles that flow outward from the sun into the solar system
Why does the solar wind exist?
- Because the glasses in the corona are so hat and speedy that they can’t be held back by solar gravity
Describe the density of the solar wind
extremely low
Where does solar wind emerge
The corona has loops, plumes and both bright and dark region. The large dark regions are coronal holes. In these regions, magnetic field lines stretch far out into space away from the sun rather than looping back to the surface.
What protects earth from solar winds
atmosphere
Where does the solar wind come to earth
at the north and south magneticc poles (Here charged particles accelerated by the solar wind can follow the field down into our atmosphere. As the particles strike molecules of air, they cause them to glow, producing beautiful curtains of light called the auroras
Cause of Sunspots
- increased magnetic activity
Why do sunspots look darker
Because they are cooler then then the spots around them
Two parts of developed sunspots
- umbra (inner darker core)
penumbra (surrounding less dark region)
differential rotation
The sun doesn’t rotate at the same rate because it is a gas
The sunspot cycle
The sunspots are much greater at sometimes then others (sunspots maximum) then at other times (sunspots minimum) . The sunspots maxima occurs about every 11 years
How is the solar magnetic field measured
- using a property of atoms called the Zeeman effect
Zeeman effect
- splitting of lines of energy levels in the presence of a magnetic field
Sunspots observed in pairs (or groups containingg two principal spots…
…seek opposite polarities (one seeks north magnetic pole other seeks south). they will switch from cycle to cycle.
Magnetogram
A visual representation of the sun;s magnetic fields
How can we see the relationship between the sunspots and the Sun’s magnetic field
magnetogram
What generates the Sun’s magnetic field
Sun’s dynamo (a dynamo is a machine that converts kinetic energy into electricity)
How does the dynamo turn kinetic energy into electricity
- source of kinetic energy is the churning of turbulent layers of ionized gas within the Sun’s interior that we mentioned earlier. These generate electric currents- moving electrons- which in turn generate magnetic fields
How does the Sun change during each solar cycle
- differential rotation and convection twist and distort magnetic fields so that they grow and decay, regenerating with opposite polarity approximately every eleven years
What explains why the leading and railing sunspots in an active region have opposite polarity
magnetic loops
Why are sunspots cooler and darker then the regions without strong magnetic fields
- forces produced by the magnetic fields resist the motions of the bubbling columns of rising hot gases. Since these columns carry most of the heat from inside the Sun to the surface by the means of convection, and strong magnetic fields inhibit this convection, the surface of the sun is allowed to cool
How do we study changes in the chromosphere during a solar cycle
emission lines
How do we study changes in the corona during a solar cycle
- can be studied by observations of X-rays and UV light and other wavelengths at high energies
plages
- bright regions within the chromosphere that have higher temps and densities in contrast to their surroundings
prominences
graceful loops of plasma
Solar Flare
Rapid erruption on the surface of the sun
When do flares (seem) to occur
When magnetic fields pointing in opposite directions release energy by interacting with and destroying each other
What do sunspots flares and bright regions in the chromosphere and corona thend to have in common
- they have sim longitudes and latitudes but are located at different heights in the atmosphere
A place on the sun where flares are more likely to occur
active region
space weather
- weather due to the effect of the solar storms on earth. When weather is bad, our technology is at risk
3 most common types of space weather (in order of least disruptive to most)
coronal holes, solar flares and CMEs
How do coronal holes cause intense changes in space weather
- they allow solar wind to flow freely from the sun, unhindered by solar magnetic fields. When they reach earth it causes Eart’s magnetosphere to contract and then expand as the solar wind passes by
How do solar flares interact with earth
shower the upper atmosphere of earth with X-rays, energetic particles, and inteense UV radiation. The X-rays and UV radiation can ionized atoms in Earth’s upper atmosphere and the freedom elections can build up a charge on the surface of a spaccraft. When this static charge discharges it can damage electronics in the space craft
How do CMEs damage earth
- When a CME reaches Earth, it distorts Earth’s magnetic field. Since a changing magnetic field induces electrical current, the CME accelerates electrons.
What harm does CME do to earth
- these electrons can penetrate deep into satellites and harm or destroy them.
- affects our technology
- exposes us to more radiation
How do we minimize effects of solar storms
- advanced warning (relate changes in the appearance of small active regions and changes in local magnetic fields on the sun to subsequent eruptions.
Marauder minimum
prolonged sunspots minimum
Why Is the energy output from the Sun during a solar cycle so high only vary about 0.1% yet there are global temperature changes
The level of solar activity may have other effects (ie the sun’s total energy output may only vary about 0.1% during the time of the cycle but its extreme UV light is 10x higher at a max then a min)
What does the increased amount of UV light at the time of a solar max affect?
The chem and temp structure of the upper atmosphere. One effect might be a reduction in the ozone layer and a cooling of the stratosphere near the Earth’s poles. This in turn could change the circulation patterns of winds aloft and hence, the tracks of storms. T
What does the equation E=mc^2 mean?
Conversion of matter into energy
What is the source of the Sun’s heat and light?
Conversion of mass into energy
What are the fundamental components of atoms?
proton, neutron and electron
For each particle there is a corresponding…
antiparticle. If the particle carries a charge, its antiparticle has the opposite charge.
What is the anti particle to the electron
positron (same mass but positively charge)
What happens when an antiparticle comes in contact with it’s corresponding particle
The original particles are converted into energy
Where is antimatter created
In the core of stars
Why did Wolfgang Pauli suggest there might be another type of elementary particle
Bcuz energy seemed to disappear when certain types of nuclear reactions took place, violating the law of conservation of energy
Neutrino
- perhaps a so far undetected particle (given the name neutrino) carries away “missing energy”
Why are neutrinos hard to detect
- they are transparent to most thingss.
How are particles held together
strong nuclear force
What happens if particles come together under the strong nuclear force and unite to form an atomic nucleus
some of the nuclear energy is released (energy released is called binding energy of nucelus)
What happens when binding energy is released
the resulting nucleus has slightly less mass than the sum of the masses of the particles that come together to form it
Which atoms is binding energy the greatest for?
Atoms with a mass near that of the iron nucleus (with a combined number of protons and neutrons that equal to 56) and less for both the lighter and heavier nuclei
Fusion
joining atomic nuclei
Fission
breaking up atomic nuclei into lighter ones
How is energy in the sun created
“roll” some nuclei together and join them via nuclear fusion. This will cause them to lose some of their mass, which then turns into energy. However, every nucleus beyond simple has two or more
Most protons have two or more protons and sense like charges repel how do they get together
If they get within striking distance of the nuclear force they will then come together with a much stronger atraction
How do protons get within striking distance
extreme heat makes them move faster and therefore fuse
Step one in three step process that takes four H nuclei and fuses them together to form a single helium nucleus
- 2 protons combine to make a deuterium nucleus (an isotope) In effect, one of the original protons converts into a neutron. Electric charge has to be conserved in nuclear reactions, and it is conserved in this one. A positron emerges from the reaction and carries away the positive charge originally associated with one of the protons
Step two in three step process that takes four H nuclei and fuses them together to form a single helium nucleus
proton proton chain
2 positrons collide and one turns into a neutron releasing a positron and a neutrino
The neutron produced in the first step combinds with a proton, forming deuterium (isotope of hydrogen)
Another proton collides with the deutrium nucleas
Why was the Sun’s energy source a major mystery?
Chemical and gravitatonal energy sources could not explain how the Sun could sustain
its luminosity for more than about 25 million years
Why does the Sun shine?
The Sun shines because gravitatonal equilibrium keeps its core hot and dense enough
to release energy through nuclear fusion.
What is the Sun’s structure? -From inside out, the layers are:
- Core
- Radiaton Zone
- Convecton Zone
- Photosphere
- Chromosphere
- Corona
How does nuclear fusion occur in the Sun?
-The core’s extreme temperature and density are just right for nuclear fusion of hydrogen to
helium through the proton-proton chain
-Sun releases energy by fusing four hydrogen nuclei into one helium nucleus
- Gravitatonal equilibrium acts as a thermostat to regulate the core temperature because fusion
rate is very sensitve to temperature
How does the energy from fusion get out of the Sun?
- Randomly bouncing photons carry it through the radiaton zone
- Rising of hot plasma carries energy through the convecton zone to photosphere
How do we know what is happening inside the Sun?
Mathematcal models agree with observatons of solar vibratons and solar neutrinos
What causes solar actvity?
Stretching and twistng of magnetc feld lines near the Sun’s surface causes solar
actvity
Solar actvity is like “weather”:
Sunspots, Solar Flares, Solar Prominences
Sunspots :
- r cooler than other parts of the Sun’s surface (4000 K); Are regions with strong
magnetc felds - Magnetc actvity causes solar fares that send bursts of X-rays and charged partcles into space.
- Magnetc actvity also causes solar prominences that erupt high above the Sun’s surface. Corona
appears bright in X-ray photos in places where magnetc felds trap hot gas
How does solar actvity afect humans?
Bursts of charged partcles from the Sun can disrupt communicatons, satellites, and
electrical power generaton
How does solar actvity vary with tme?
Actvity rises and falls with an 11-year period
Luminosity:
Amount of power a star radiates (energy per second = wats)
Apparent brightness:
- Amount of starlight that reaches Earth (energy per second per square meter)
- Luminosity passing through each sphere is the same
- Area of sphere: 4π (radius)2 ; Divide luminosity by area to get brightness:
The relationship between apparent brightness and luminosity depends on distance
luminosity= 4 pi (distance)^2 x brightness
what does p symbolize
parallax angle
d (in light years) is equal to how many p’s
(come back to this)
Propertes of Thermal Radiaton
- Hoter objects emit more light per unit area at all frequencies.
- Hoter objects emit photons with a higher average energy.
Hotest stars:
50,000 K;
Coolest stars:
3,000 K
Sun’s temp
Sun’s surface is 5,800 K
Lines in a star’s spectrum correspond to a spectral type that reveals its temperature
(Hotest) O B A F G K M (Coolest)
How do we measure stellar luminosites?
- If we measure a star’s apparent brightness and distance, we can compute its luminosity with
the inverse square law for light - Parallax tells us distances to the nearest stars
How do we measure stellar temperatures?
A star’s color and spectral type both refect its temperature
How do we measure stellar masses?
Newton’s version of Kepler’s third law tells us the total mass of a binary system, if we can
measure the orbital period (p) and average orbital separaton of the system (a
An H-R diagram plots the:
luminosity and temperature of stars:
What is a Hertzsprung-Russell diagram?
An H-R diagram plots stellar luminosity of stars versus surface temperature (or color or spectral
type)
What is the signifcance of the main sequence?
Normal stars that fuse H to He in their cores fall on the main sequence of an H-R diagram
– A star’s mass determines its positon along the main sequence (high-mass: luminous and blue;
low-mass: faint and red)
H-R diagram depicts
Temperature
Color
Spectral Type
Luminosity
Radius
A star’s full classifcaton includes :
spectral type (line identtes) and luminosity class (line shapes, related
to the size of the star):
Main sequence correlation of luminosity and temp
Luminous main-sequence stars are hot (blue)
Less luminous ones are cooler (yellow or red)
Which are massive? Hot blue stars or cool red ones?
Mass measurements of main-sequence stars show that the hot, blue stars are much more massive than
the cool, red ones
The mass of a normal, hydrogen-burning star determines:
its luminosity and spectral type!
How can you find Luminosity:
from brightness and distance
How can you find Temperature:
from color and spectral type 3,000 K - 50,000 K
How can you find Mass:
from period (p) and average separaton (a) of binary-star orbit
0.08 MSun - 100 MSun
