April 19, 2005, jebPRELIMINARY
Outline
- Central temperature: 15,000,000 K
- Surface temperature: 6,000 K
- Distance from Earth: 150,000,000 kilometers
(1 Astronomical Unit)
- Size: 1,400,000 kilometer diameter
- Mass: 2 x 10 30 kilograms
(300,000 x the Earth's mass)
- Average density: 1400 kg/m3(1.4 x water)
- Solar energy reaching Earth: 1400 Watts/m2 (solar constant)
- Total Luminosity of the Sun
- equivalent to the energy flow through a
sphere surrounding the Sun
- The surface area of this sphere is 2.8 x 10 23 m2
- So, the total luminosity is:
- 1400 Watts/m2 x 2.8 x 10 23 m2
- = 4 x 10 26 Watts
- Core
- radius = 0 to 200,000 km
- Temperature(inner radius) = 15,000,000 K
- Energy generated by nuclear fusion
- Radiation Zone
- radius = 200,000 to 500,000 km
- Temperature(inner radius) = 7,000,000 K
- Energy transported by electromagnetic radiation
- Convection Zone
- radius = 500,000 to 696,000 km
- Temperature(inner radius) = 2,000,000 K
- Energy transported by convection
- Photosphere
- radius = 696,000 to 696,500 km
- Temperature(inner radius) = 5800 K
- Electromagnetic radiation escapes - visible surface of the Sun
- Chromosphere
- radius = 696,500 to 698,000 km
- Temperature(inner radius) = 4500 K
- Cool lower atmosphere
-
Transition Zone
- radius = 698,000 to 706,000 km
- Temperature(inner radius) = 8000 K
- Temperature rising rapidly
- Corona
- radius = 706,000 km out
- Temperature(inner radius) = 1,000,000 K
- Hot, low-density upper atmosphere
- Solar Wind
- radius = 10,000,000 km out
- Temperature(inner radius) = 2,000,000 K
- Material escaping and flowing through the solar system
The Energy generation of the Sun is tremendous
For about 5 billion years, the Sun has been emitting
- this is about 3 x 10 13 Joules per kilogram
- hydrcarbons -> 40-50 MegaJoules/kilogram
- dynamite -> about 5 MegaJoules/kilogram
- What can possibly be the source of so much energy?
Thermonuclear Fusion
H + H + H + H - ---> He (effectively)
with slight loss of mass
The small amount of lost mass turns into energy
Following Einstein's famous equation:
(hydrogen burning)
(1 million times the energy of TNT per unit mass)
Hydrostatic Equilibrium
- Tremendous weight of the mass of the Sun presses inward under the force
of gravity.
- Enormous pressure (generated by Thermonuclear fusion) inside the Sun pushes back.
- Thermal Equilibrium
- Energy can be transferred by three processes:
conduction, convection, and radiation
- Only convection and radiation are important in
the Sun
- Transport of heat to the Solar surface
- Energy is transported from the core to the Solar surface, through
the Radiation Zone and the Convection Zone
- Transport can take tens of thousands of years
- Radiation Zone
- Radiation passes freely through the Radiation Zone to the base
of the Convection Zone
- Convection Zone
- Circulation of Solar mass moves heat outward
-
Photosphere
- Layer from which most
visible light comes
-
- radius about 700,000 km
- temperature about 6000 K
-
absorption lines
reveal the composition of the Sun
- tens of thousands of spectral lines have been observed and catalogued
- 67 elements have been identified
- Ten most common elements:
- Hydrogen (91.2 % of atoms)
- Helium (8.7% of atoms)
- Oxygen (0.078%)
- Carbon (0.043%)
- Nitrogen (0.0088%)
- Silicon (0.0045%)
- Magnesium (0.0038%)
- Neon (0.0035%)
- Iron (0.0030%)
- Sulfur (0.0015%)
-
Chromosphere
-
- Above the Photosphere
- about
2,000 km thick
- dominated by emission lines
- Corona
-
-
Outermost region
- millions of kilometers thick
- temperature about
1,000,000 K
- very "thin" ionized gas
Sun
"rings" like a bell
Measuring vibrations on the surface is a link to the interior
-
Photosphere
-
-
"granules" - giant bubbles at top of convection zone
- Chromosphere
-
-
"spicules" - spears of gas spurting out 10,000 km
- Corona
-
- heated tremendously (1,000,000 K at inner radius) by magnetic fields
- beautifully visible during
solar eclipse
- Solar Wind
-
- outflow of material, captured in the magnetic field
Neutrinos are produced in
nuclear reactions
- Nuclear reactors on Earth
- Thermonuclear Fusion in the Sun
- Supernova explosions
- Particle Accelerators in Laboratories
Observations of Solar Neutrinos passing through the Earth
Properties of Neutrinos
- carry no charge
- carry very little (if any) mass
- Interact
hardly at all
(neutrinos from the Sun usually pass through the entire Earth freely!)
Fewer neutrinos are detected than are expected from our model of the Sun
- We now understand this as a change in the properties of neutrinos
- Our Model of the Sun appears OK
