1. Solar structure:

Core

Interior

Convection zone

Photosphere - the solar disk - very thin

5800 degrees (K)

Chromosphere - lower atmosphere, where absorption lines are formed

(transition region)

Corona - upper atmosphere - very hot and tenuous

How is heated?

Energy from magnetic fields?

trends of temperature and density

2. Energy transport

radiation:

free streaming of photons or other energetic particles

convection:

overturning of cells of matter at different temperatures

Solar radiative zones:

most of the interior of the sun

Core

Interior

and, the Photosphere

Convective zones:

outermost layer of the interior before the photosphere

convective cells get smaller at larger radii

(cooler temperatures, lower densities)

3. Solar surface

Due to, or shaped by magnetic fields:

sunspots

slightly cooler regions of photosphere

300-1300 degrees (K) cooler

spicules

prominences

flares

Due to convection:

granules (granulation)

roughly 1000 km in size

super-granules (super-granulation)

roughly 30,000 km in size

4. Sunspot and Solar cycles

11 years - sunspot cycle (minimum and maximum activity)

22 years - solar cycle (orientation of magnetic fields)

Why?

differential rotation

twisting of field lines

5. Solar Guts - Fusion Revisited

Incredible energy production from: fusion +

(i) E = mc²

(ii) total matter and energy are always conserved

The proton-proton chain:

6 protons (6 H nuclei)

2 protons + 2 neutrinos + 2 positrons + He-4

where,

He-4 (Helium-4) = 2 protons + 2 neutrons

neutrinos: almost massless

positrons = anti-electrons

- weigh much less than proton or neutron

Add up input and output mass:

input mass > output mass

Energy MUST be released

Mass difference is primarily due to the difference in the mass of the proton and neutron (neutron is lighter )

mass(proton) > mass(neutron)

6. Solar neutrinos

- a disturbing puzzle

- where are they? (why don't we detect them?)

- neutrino oscillations?

7. Age of the Sun

Per fusion event (4 protons Helium) :

m = mass(proton) - mass(neutron)

2 x m = 4.8 x 10^-29 kg

c² = 9 x 10¹⁶ m² /s²

E = mc² = 2 x m c² = 4.3 x 10^-12 Joules (kg m²/s²)

lifetime = [total mass]

x [energy release per unit mass] / [energy radiated per sec]

radiant energy: 3.9 x 10²⁶ Joules per s

total mass: 2 x 10³⁰ kg

energy per unit mass: 6.4 x 10¹⁴ J per kg

lifetime: about 10 billion years

(a) flares

(b) fusion

(c) sunspots

(d) radiation

(e) spicules

(a) mass and energy are convertible and conserved overall

(b) the neutrino can pass through light-years of lead

(c) fusion drives convection in the outer layers of the sun

(d) the mass of the protons are less than the resulting neutrons

(e) proton-proton interactions conserve angular and linear momentum