Core: Central energy producing region
Thermonuclear fusion occurs here. Energy
transport by radiation.
Temperature: ~16 x 106 K
Density: ~160 g/cm3
large region of
interior photons scattered on the way to the solar
Temperature: ~8 x 106 K
Density: ~20 g/cm3
Convective Zone: Transition region between interior
and surface. Energy transport by convection.
Temperature: ~5 x 105 K
Density: ~0.01 g/cm3
Photosphere: Visible surface of the Sun.
Convective "bubbles" from below visible
Granulation. Location of Sunspots.
Temperature: ~5.8 x 103 K
Density: ~4 x 10-7 g/cm3
Chromosphere: Beginning of solar "atmosphere".
Location of prominences and solar flares.
Temperature: ~5 x 104 K
Density: ~8 x 10-8 g/cm3
Transition Region: Region between corona and chromosphere.
Temperature changes from ~50,000 K in chromosphere to ~2 x 106 K in corona over
a few tens of kilometers!!!!
Corona: Hot, thin, large solar "atmosphere". Coronal holes are source of the solar
Temperature: ~2 x 106 K
Density: ~1 x 10-14 g/cm3
Diagram of convection.
Regions of intense magnetic fields.
Temperature ~ 4200 K cooler than photosphere, which makes them appear as dark spots.
Can be used to measure solar rotation (25 days at equator, 31 days at poles).
Chromosphere contains many dark, brush-like spikes that protrude upward. These are called spicules.They are "jets" of gas surging away from the sun at 20 km/s.
They attain heights of ~7000 km .
Huge, arching columns of gas often appearing above sunspots. Prominences are regions along a magnetic field line where conditions are right for light to be emitted.
Flares release large numbers of particles into the corona.
There are three ways in which energy can be transported from one place to another:
Energy is transported by photons.
Energy loss by scattering and absorption by atoms.
Very efficient mechanism in stars (also efficient on cloudless evenings very chilly nights).
Energy transported by bulk motion of mass.
Important mechanism in stars.
Very poorly understood process.
Energy transport by atoms colliding with one another, gaining and releasing energy.
Efficient mechanism in solids, but not in stars.
Examples of Energies:
Energy to lift a sheet of paper 1 cm: ~ 1 erg
Chemical energy in a barrel of oil: ~ 1017 ergs
Nuclear energy in a gram of water: ~ 7 x 1019 ergs
Total energy emitted by Sun in its lifetime: ~ 1050 ergs
Total energy emitted by single supernova: ~ 1051 ergs
There are 3 types
of energy of concern to us here:
Energy resulting from the motion of matter when interacting with other matter.
Energy resulting from, a change in the electron structure of atoms when bonding with other atoms. "Burning".
Energy resulting from changes in the nuclear structure of atoms.
Gravitational Energy As A Source Of Solar Energy:
energy ÷ Luminosity = How long sun could be powered.
(1 × 1048 ergs) ÷ (4 × 1033 ergs) = Could power the sun for about 100 million years.
Chemical Burning As A Source Of Solar Energy:
Total chemical energy ÷ Luminosity = How long sun could be powered.
(1 × 1046 ergs) ÷ (4 × 1033 ergs) = Could power the sun for about 10,000 years.
Until the late 1800s, gravitational energy was thought to be sufficient, since it was not thought that the Universe was that old.
However, for two
reasons it was later thought that something more than gravitational
powered the sun:
Darwin (1809-1882): Theories of evolution required much longer than 108 years for evolution to
proceed.Geological dating of rocks indicated that the Earth was several x 109 years old.
So What Powers
Einstein, getting energy from hydrogen fusion, came up with the following equation that explains it all:
E = Energy, m = mass, c = speed of light
Fundamental Structure Of The Atom:
P+ Proton (charge: +, mass: 1.67 × 10-24 g)
n Neutron (charge: Ø, mass: 1.67 × 10-24 g)
e- Electron (charge: -, mass: 9 × 10-28 g)
The Proton-Proton Chain:
High Temperatures Are Needed For Fusion. Why? Recall that like charge repel.
Temperature required for the p-p chain: T ~ 107 K
Temperature is found in the Sun's core, where density is ~ 160 g/cm3 .
Even at this density, reaction probability is very low.
Single proton takes ~ 7 x 109 years before reacting.
Large number of protons make up for low probability.
Why doesn't the Sun collapse under its own weight, or blow it
self apart because of nuclear
Gravitational forces produce inward pressure.
When the two pressures are equal (but opposite
directions) the star (Sun) is stable against collapse -
Energy Output Of
The total amount of energy, in a given time, over a given area above the Earth's atmosphere,
that reaches us from the Sun is called: Solar Constant.
Numerically it is ~ 2 calories/cm2/minute.
Models suggest that a 1% change will result in a 1º-2º change in Earth's temperature.
During the last ice age (~20,000 years ago), Earth was ~5º cooler than today.
A 10% (~10º) change would result in an ice covered Earth.
Is The Solar Constant, Constant?
The Sunspot Cycle:
The number of sunspots observed on the Sun varies in an 11 year cycle called the Sunspot Cycle.
1.Differential rotation winds up the magnetic field.
2.Field becomes tangled and breaks through the surface sunspot
3.After 11 years, field decays.
4.Differential rotation winds up the magnetic field.
5.Newly organized field is reversed.
moving electrical charges.
2.Magnetic fields around planets/Sun resemble those around bar
3.Lines indicating direction of the magnetic field are called magnetic
4.Planetary and solar magnetic fields are thought to arise in a fluid,
5.Magnetic fields arise from circulating electrical currents generated by
the object's rotation.
The Sunspot Cycles:
One theory that attempts to explain the cycle is the
bring them to the surface.
Magnetic fields appear as sunspot pairs.
Magnetic fields decay and switch polarity.
Charged particles move along magnetic field lines - they cannot
holes are regions
where magnetic field lines are open, that is, they do not return to
surface. Charged particles can, therefore, escape the Sun in the form