oursunthestar Flashcards
Chemical burning
cannot account for the Sun’s luminosity
Gravitational contraction
contradicts Earth’s age
The Sun is not (just) a ball of gas
it is made of plasma
The Sun generates energy via
nuclear fusion reactions
nuclear fusion reactions SOL
Hydrogen (H) is converted into Helium (He) in the core
Mass difference between He & H transformed into energy—>Einstein’s theory: E = mc2
Solar mass will provide enough energy to
shine for 10 billion (b) years
About 5.5b more years to go!
The Sun was born ~4.5b years ago from a
a collapsing gas cloud.
The core became hot & dense enough for nuclear fusion
get very annoying and mathy about sun energy
Ignited fusion produces energy (EFusion) in the Sun’s interior.
Ultimately, most of it is radiated away (EOutputRadiation) & the resulting heat (Efusion–EOutputRadiation) exerts an outward pressure.
This pressure perfectly balances
inward force of gravity. This balance is called gravitational equilibrium (or
hydrostatic equilibrium)
Pressure is largest deep inside the Sun
get very annoying and mathy about sun energy part 2 you nerd
In conclusion, the Sun’s steady behaviour is due tothe SOLAR THERMOSTAT = the complex equilibrium
between:
Outward pressure (due to the difference
between energy generated via fusion and that
radiated away)
The inward push of the gravitational force
Striking a Balance (cont’d)
Composition (weight%): 70% H2, 28% He
+ 2% heavier elements, of which O, C & Fe are the most important
Surface temp.: 5800 K (average) but 4000 K in sunspots
Core temp.: 15×10^6 K = 15mK
Composition of the Sun (and stars in general) is deduced from
spectroscopic measurements.
Notice the presence of black lines in Sun’s spectrum:
absorption lines due the quantized energy levels of the component atoms.
faculae
slightly brighter and hotter areas T ~ 5900K
talk about the layers of the sun, lets go from out to in
photosphere, chromosphere, convection zone, radiation zone, core
Solar Core
Energy generation through nuclear fusion takes place ONLY in the core (just ~10% of total Sun’s mass!)
T = 15 m K, Depth = from centre to 0.25RSun
Density: >100 times of water.
Pressure: 200b times that on Earth’s surface.
Energy produced takes 100,000s years to reach surface!
The solar core is a cosmic crucible in which one chemical element is created from another
.
What is nuclear fusion?
Process by which heavier nuclei are created from combining lighter nuclei. Electromagnetic (EM) force causes nuclei to repel each other. To fuse, nuclei must move very fast to overcome EM force--- > Fusion needs VERY high temperatures & pressures When nuclei touch, nuclear force binds them together.
Hydrogen fusion in the Sun’s core 1
Step 1: 2 protons fuse to form a deuterium nucleus (1 proton + 1 neutron) and emit 1 neutrino (ve) and 1 positron (e+)
- Since a proton is converted into a neutron, total nuclear charge is reduced
- The lost positive charge (for overall balance of charge) is carried off by a positron (antielectron = antimatter particle similar but opposite to a electron)
- Neutrinos are emitted for conservation of lepton
number (nr. of emitted e+ & ve must be the same)
- This step is required twice in the overall reaction
Hydrogen fusion in the Sun’s core 2
A deuterium nucleus fuses with a proton to form the nucleus of a 3He isotope and emit a γ ray photon - This step is also required twice in the overall reaction
Hydrogen fusion in the Sun’s core 3
2 3He nuclei fuse to form a
normal 4He nucleus and release 2 protons
Hydrogen fusion in the Sun’s core - Summary
IN: 6 H
OUT: He, 2 H, 2e+, 2νe , 2γ
Hydrogen fusion in the Sun’s core - Summary 2
The overall reaction needs 6 protons to enter the reaction and
produces 1 He nucleus, neutrinos, positrons and γ radiation, and releases back 2 excess protons.
Effectively 4 H nuclei are converted into 1 He nucleus & energy is released.
Where does the solar energy come from? FUCK
Note that
Mass of He = 99.3% of (Mass of 4 H)
0.7% of mass is lost!
Lost mass converted into energy according to E = mc2.
98% → kinetic energy of particles &
γ-rays → sunlight
2% → neutrinos
600b kg (600
m tons) of H converted to 596m tons of
He every second.
4b kg (4m tons) of matter converted into energy
Negligible since Sun’s mass is 1030 kg (1027 tons = billion billion billion !)
Fusion can also produce other elements if conditions are right (T, p)
The Gradually Brightening Sun
Solar luminosity is stable over the short-term.
But luminosity slowly increases in time over the long-term.
4 H nuclei→ 1 He nucleus
Number of particles in core decreases with time
Core will contract, causing it to heat up
Fusion rate increase to balance higher gravity
New equilibrium reached at higher energy output
Models indicate solar luminosity has increased 30% since itformed 4.5b years ago.
Output increased
(↑) from 2.9×1026 W to 3.8×1026W
Models indicate solar luminosity has increased 30% since itformed 4.5b years ago.
Output increased
(↑) from 2.9×1026 W to 3.8×1026W
But luminosity slowly increases in time over the long-term.
4 H nuclei→ 1 He nucleus
Number of particles in core decreases with time
Core will contract, causing it to heat up
Fusion rate increase to balance higher gravity
New equilibrium reached at higher energy output
Interior Zones D’SOL
T < 8m K, Depth = 0.25 … 0.999 RSun
Energy transported through the interior.
Two Zones d’sol’d’interior
Radiation zone:
Convection zone:
Radiation zone:
energy moves outward primarily due to
radiative diffusion of photons
Convection zone:
energy travels upward by the rising of
hot fluid & falling of cool fluid (convection)
Boundary: yeah i dont know what this is either
T = 2mK Depth = 0.7 RSun
Methods of Energy Transport
Fusion releases most energy in the form of photons.
Deep in the Sun’s interior, plasma is very dense.
A photon moves less than 1 mm before bumping into a particle
‘Deflected’into a new random direction (actually: absorbed by a particle
and immediately re-emitted)
Bounces around in a haphazard way (random walk)—-> VERY slow outward migration known as radiative diffusion ————–> it takes hundreds of thousands of years!
Very high temperature in radiation zone
(~ 10m K)
Very high temperature in radiation zone dit moi plus
It “cools” towards the surface, reaching ~2m K at the boundary with the convection zone Photons move out primarily by randomly bouncing off particles
Plasma in the convection zone has a
has a lower temperature(<2m K)——————->absorbs photons more readily rather than bouncing them around
Bottom of zone heated
Hot gas rises to top (less dense!), cooler gas (denser) sinks to the bottom
Plasma convection transports energy to photosphere
Photosphere
T = 5,800 K, Depth = 400 km
Photosphere p1
Lowest layer of atmosphere. Density of the plasma becomes so low that photons can escape to space--------> that’s why we see the photosphere as the “surface” of the Sun Appears as a yellow surface, churns like boiling water
Photosphere p2
The convecting gas gives the photosphere the mottled appearance (solar granulation) due to the “bubbling” of the convection cells on the solar surface
AVERAGE temperature is 5,800K, but convection causes the exact value to vary significantly from place to place
This is where sunspots develop
Sunspots
Dark spots on the surface where the
temperature is cooler.
appear dark in photographs.
Sunspots
Sunspots appear dark in
photographs.
Less bright because they are cooler (4,000K) than the surroundings (5,800K).
Sunspots occur in
pairs, which cluster into groups
& rotate with the Sun.
Sunspots are ALWAYS
accompanied by faculae!
what is the length of the cycles that sunspots come and go
11yr
The solar output (total solar irradiance = TSI) does vary during
the solar cycle. Sunspots cause a temporary decrease in
TSI of as much as 0.3%. However, the net effect during periods of
enhanced solar magnetic activity is an increased TSI (with ~0.05%) because sunspots are ALWAYS accompanied by faculae
and when they disappear they transform into faculae, which are hotter ( T ~5900 K) & ‘brighter’ than the average photosphere, larger, and persist longer than the sunspots. (The opposite is true
during periods of decreased/no magnetic activity, when few/no sunspots appear)
Sun’s magnetic field switches polarity every
11 years (AVERAGE value; it
can be between 7…15 years).
Entire cycle repeats every 22
years (solar cycle).
What causes sunspots?
Answer in their spectra lines. Magnetic field is the cause. Magnetic field can alter energy levels in atoms & ions Split spectra lines (Zeeman effect) Spectra lines at sunspot are split in three. Magnetic fields can be mapped by looking for spectral line splitting on solar surface.
Charged particles moving in a magnetic field are trapped in
tight corkscrew-like helical movements around the magnetic field lines.
Magnetic field lines slow down what thing
convection
* Less heat is transported to surface so that part of photosphere is cooler
The Sun does not
rotate as a solid body
Solar equator rotates faster than
the poles
solar region periods
Period of 25 days at the equator
Period of 30~36 days at the pole
Chromosphere
T = 10,000…50,000 K, Depth/Extent = 2,500 km Middle layer of the solar atmosphere Thin layer above photosphere Radiates most of UV light Glows red due to H emission
Corona
T = 1…2m K, Depth/Extent = 600,000 km Outmost layer of Sun’s atmosphere. Hot, ionized gas surrounding the Sun Very low density & emits mostly X-rays (strongest emission right above sunspots)
Gas density in corona & chromosphere is so low that
they are not visible except during total eclipse.
Scattered faint light in corona
become visible
However, X-ray & UV from what can be seen
corona & chromosphere can be seen.
what thing has empty patches
Corona has empty patches called coronal holes → directly related to solar activity
Solar Activity
Solar activity = refers to the sum of all variable (some intermittent, some periodic) and short-lived (but
sometimes extremely intense) EXTERNAL disturbances on the Sun (such as sunspots, prominences, solar flares, etc.), NOT the constant internal processes that characterize its long-term normal behaviour and appearance (e.g. the fusion reactions and generation of energy in the core, the contorted slow random walk of photons through the radiative zone, the mass and energy transfer in the convection zone, the granulation of the photosphere, etc)
Solar Activities:
Prominences & Filaments
Gas in chromosphere & corona trapped in magnetic loops, making giant solar prominences or filaments.
Some prominences rise to heights >100,000 km.
Last for days or even weeks.
Solar Activities: Chromosphere & Corona Heating
Higher temperature above the photosphere explained by magnetic heating.
Magnetic loops shaken at their bases by turbulent motions in convection zone.
Kinked, twisted field loops deposit energy as heat in the solar atmosphere.
Magnetic fields keep the sunspots cool but make the overlying plasma of the chromosphere & corona hot.
Observations confirm connection between magnetic fields & the structure of chromosphere & corona.
Solar Wind
Magnetic field lines in coronal holes ultimately snap out and project out into space like broken rubber bands, allowing particles spiraling along them to escape the Sun altogether.
Solar Wind 2
The particles streaming outward from the corona form the solar
wind = Stream of (plasma consisting of) electrons (e– ), protons ( p + ), He nuclei & other ions flowing out from the Sun (~500km/s).
Solar Wind 3
The solar wind is constantly produced as a result of the normal processes taking place inside & outside the Sun, with intensity variations due to the Sun’s MF periodic reconfiguration and the sunspot cycle, but it is still considered a solar activity due to its outward manifestation and the wild and extreme fluctuations it can have as a direct result of other solar activities with which it is intrinsically correlated and interdependent.
Extends out beyond Pluto (>40 AU)!
Important effects on surface, atmosphere & magnetosphere of planets.
Eventually stopped by pressure of interstellar gas
Solar Activities: flares & CMEs
When a magnetic loop “breaks’’ (snaps), short-lived but intense magnetic storms are produced.
Most dramatic of these storms are solar flares =
tremendous explosions on the surface of the Sun
Release bursts of X-rays & fast-moving charged particles
Coronal mass ejections (CMEs) are huge bubbles of
gas threaded with magnetic field lines that are ejected
from the Sun over the course of several hours.
They disrupt the flow of the solar wind and produce
disturbances that strike the Earth with sometimes catastrophic results: geomagnetic storms, disrupt radio communications & electrical power delivery,
damage satellites
Often associated with solar flares and prominence eruptions but can also occur in the absence of either of these processes.
Their frequency varies with the sunspot cycle.
When a magnetic loop “breaks’’ (snaps),
short-lived but intense magnetic storms are produced.
Most dramatic of these storms are solar flares = tremendous explosions on the surface of the Sun
Release bursts of X-rays & fast-moving charged particles
Coronal mass ejections (CMEs) are
huge bubbles of gas threaded with magnetic field lines that are ejected
from the Sun over the course of several hours.
Coronal mass ejections (CMEs)
They disrupt the flow of the solar wind and produce
disturbances that strike the Earth with sometimes catastrophic results: geomagnetic storms, disrupt radio communications & electrical power delivery, damage satellites
Often associated with solar flares and prominence eruptions but can also occur in the absence of either of these processes.
Their frequency varies with the sunspot cycle
How do we study the Sun?
Motion of sunspots and Doppler shifts
solar rotation.
Satellites observe the Sun in different parts of the spectrum
X-rays, ultraviolet (UV), visible, infrared (IR) (Earth-based or
satellites)
How do we know what is going on INSIDE the Sun?
The Sun’s interior is opaque.
Cannot see underneath its surface with light
Use mathematical models of the Sun.
Models of temperature, pressure & density vs. depth
Values are calculated using known laws of physics
Tested against observable quantities
From solar vibrations measurements.
Observe “sunquakes” in photosphere using Doppler shifts:
helioseismology
Motion of sound waves checked against interior conditions
predicted by models
How do we know what is going on in the Sun? 2
From solar neutrinos.
Trillions of solar neutrinos pass through us every second
Reach us minutes after being produced
Stopping a neutrino requires a slab of Pb >1 light year thick (1 inch of Pb for X-ray stopping)
Very difficult to detect!
VERY large detector to capture just a few.
Solar neutrino problem: initially only 1/3 of the predicted number of neutrinos was captured
Neutrinos are of 3 types. Fusion reactions in the Sun’s core produce only 1 type, but some change in the other 2 types during their trip from the Sun’s core to the Earth
Detection of all types of neutrinos (Sudbury Neutrino
Observatory – Canada) proved fusion in Sun’s core.
Magnetosphere distortion
1st effect of the interaction between solar wind & Earth/ANY planet
Magnetosphere:
The Earth’s magnetic field reaches 36,000
miles into space and would
normally look like this — . . —
Magnetosphere: , 2
However, due to the constant bombardment and pressure at which is subjected to by the solar wind, it actually looks like this —-> looks like a spider on spiderman’s shirt lol
The magnetic storms + Northern & Southern Lights on Earth are also caused by
magnetic reconnection: magnetic field lines breaking
and reconnecting with each other. This process can explosively convert magnetic energy to heat and kinetic energy
Aurora:
:
2nd effect of the interaction between solar wind & Earth
Why and how are aurorae generated?
Earth’s mgn. field is distorted by the solar wind: compressed on the sunfacing side (bow shock) and drawn out on the opposite side
(magnetotail).
The solar wind can even cause the sudden breaking and rearranging of
the magnetic field lines (magnetic reconnection).
The charged particles of solar winds are either deflected around the
Earth or captured by the Earth’s mgn. field —-> in the latter case, they travel along the field lines —>
Currents of charged particles within the magnetic fields travel toward both poles (focused at polar cusps)
—–> This is why there are simultaneous auroras in both hemispheres. These currents are called Birkeland currents
The solar wind can even cause the
sudden breaking and rearranging of the magnetic field lines (magnetic reconnection).
Earth’s mgn. field is distorted by the solar wind:
: compressed on the sunfacing side (bow shock) and drawn out on the opposite side (magnetotail).
Currents of charged particles within the magnetic fields travel toward both poles (focused at polar cusps)
This is why there are simultaneous auroras in both hemispheres. These currents are called Birkeland currents.
Why and how are aurorae generated? (cont.d)
Descending e− currents hit air molecules (oxygen & nitrogen ions)
→ their energy is transferred to these ions
this causes e− within these ions to become excited (i.e. move from low-energy to high-energy orbitals)
-> excited ions relax (i.e. e− return to low energy orbitals) by radiating the excess the energy as light. This light makes up the aurora.
The different colors come from light radiated from downward transitions (de-excitation) between different energy levels of various atoms/ions.
Descending e− currents hit air molecules (oxygen & nitrogen ions)
→ their energy is transferred to these ions
this causes e− within these ions to become excited (i.e. move from low-energy to high-energy orbitals)
-> excited ions relax (i.e. e− return to low energy orbitals) by radiating the excess the energy as light. This light makes up the aurora.
The different colors come from light radiated from downward transitions (de-excitation) between different energy levels of various atoms/ions.
What are the van Allen radiation belts?
They are 2 regions of radiation that encircle the Earth.
The two belts are not static but of variable size: they expand and shrink.
Result from Earth’s magnetic field interaction with the solar wind: The magnetic field traps particles, accelerating them and forming belts of radiation.
When e− currents travel along the field lines, they pick up more energy due to a resonant-like process: trapped lower-energy e− radiate energy as radio waves at just the right frequency to hit a newly coming trapped particle each time it comes around, at just the right time, so after each cycle it goes increasingly faster & faster. Eventually, these e− approach relativistic speeds!—->This mechanism also creates the van Allen radiation belts
Whene− currents travel along the field lines, they pick up more energy due to a resonant-like process:
trapped lower-energy e− radiate energy as radio waves at just the right frequency to hit a newly coming trapped particle each time it comes around, at just the right time, so after each cycle it goes increasingly faster & faster. Eventually, these e− approach relativistic speeds!—->This mechanism also creates the van Allen radiation belts
What are the van Allen radiation belts?
well there’s an outer one and an inner one
Both belts are filled with plasma but the composition
differs between the 2 belts and also is affected by solar radiation.
The inner belt has a relatively stable composition. It contains mostly protons.
The outer radiation belt varies in size and shape and consists almost entirely of accelerated e− .
A 3rd, temporary belt, was discovered very recently just before being dispersed by shockwaves from the Sun.
What causes solar activity?
The dislocation, stretching, twisting and snapping open of magnetic field lines at the Sun’s surface (flares) or massive eruptions of matter (CMEs).
How does solar activity affects/interacts with Earth?
Distorts Earth’s magnetosphere.
Causes aurorae (northern & southern polar lights).
Gives rise to the radiation belts around the Earth.
How does solar activity affect humans?
Unshielded humans in space are seriously affected by the solar wind as its high-energy particles have ionizing properties that damage living matter and cause radiation poisoning.
Humans on Earth are unaffected: we are (usually) shielded by Earth’s magnetic field.
The bursts of charged particles from the Sun can disrupt communications, satellites, and even electrical power generation.
How does solar activity vary with time?
Activity rises and falls in 11-year cycles
