"Our sun is the greatest source of energy available to us
and the simplest to obtain.
We have the means and the technology to do this.
Currently we use other sources of energy most of which are finite,
polluting and most importantly could be put to the better use of
From a "value added" economic perspective fossil fuel resources would
be much better utilised in making much more valuable plastics,
chemicals, lubricants... in the long term.
The long term interests of humanity offset by the short
term interests of the few. Repeated lessons in history not
Yet in the western democracies easily resolved by the simple casting
of an informed vote."
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
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
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
Granulation: Provide evidence of convection below solar
Diagram of convection. Sunspots:
Regions of intense magnetic fields.
Temperature ~ 4200 K cooler than photosphere, which makes them appear as
Can be used to measure solar rotation (25 days at equator, 31 days at
Umbra - dark inside, Penumbra - lighter outside
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.
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.
Occasionally, kinks and stresses occur on magnetic field lines discharging
amounts of energy (known as Solar Flares). The amount of energy
released is equivalent to a 2 billion megaton bomb. 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
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
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:
Total gravitational 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
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 energy 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 The Sun?
Einstein, getting energy from hydrogen fusion, came up with the
following equation that explains it all:
E = mc2
E = Energy, m = mass, c = speed of
Fundamental Structure Of The Atom:
P+ Proton (charge: +, mass: 1.67 × 10-24 g)
n Neutron (charge: Ø, mass: 1.67 ×
e- Electron (charge: -, mass: 9 × 10-28 g)
The Proton-Proton Chain: Nuclear Fusion:
High Temperatures Are Needed For Fusion. Why? Recall that like
High temperatures (energy) are required in order to overcome this
repulsion.Actual details require descriptions provided by Quantum
Mechanics. 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
Why doesn't the Sun collapse under its own weight, or blow itself apart
because of nuclear fusion?
Core nuclear processes produce outward pressure.
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 Sun:
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:
Numerically it is ~ 2 calories/cm2/minute.
Models suggest that a 1% change will result in a 1º-2º change in Earth's
During the last ice age (~20,000 years ago), Earth was ~5º cooler than
A 10% (~10º) change would result in an ice covered Earth.
1.Magnetic field: term that describes regions of space modified by
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.
Differential rotation and convection twist interior magnetic fields and
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 cross