Chapter 14 in the 4th edition of Bennett et al.
The Sun
Introduction
The Sun is big (Size comparison)
The Sun is hot
The Sun is bright
Why the Sun is bright:
Nuclear burning in the Sun's core
Nucleus = protons + neutronsOvercoming electric repulsionThe Reaction in action
Problem:
The Sun produces 3.8 x 1026 Joules/second. This is
generated
by converting mass into energy. How much mass is converted
to energy every second?
Is that the same as the amount of hydrogen converted to helium
every second? Fusion =/= Fission
Nuclear burning only happens in the Sun's core (1/4 Sun's radius):
The pressure is greatest in the core and decreases with radius
(called hydrostatic equilibrium or gravitational equilibrium)
Weight of material above causes compression of material below
and pressure of material below bears the weight of the material above
cartoon of pressure countering weight of material aboveFish example of forces in balance
Pressure = density * constant (k) * Temperature
Temperature and density are highest in center (plots)
Energy "made" in the center moves from the core to the surface:
"Random walk"through the core and radiation zone
Spectrum changes -> gamma rays to wide range of photons
Radiation Zone = from 1/4 radius to 2/3 radius of Sun
Continuing outward: The convection zone
"Cool" enough to absorb photons (Temperature plot)
"bottom" of convection zone rises buoyantly
"top" of convection zone sinks
So, moves thermal energy outwards by convection
Schematic of Sun
Simulated view of top of convection zone
Photosphere (visible surface of the sun)
Photons emitted here can leave sun
Appears granulated (due to the activity in the convection zone)
Has Sunspots: image
Chromosphere
(
Schematic of Sun)
Corona (X-ray image)
How the Sun was Born:
Cloud of gas was pulled together by gravity
Cloud became smaller, denser, and hotter
Center became hot and dense enough for nuclear burning
That is when our cloud became a star, our Sun
That was 4.6 billion years ago
Our sun has enough fuel for another 5 billion years
Solar Thermostat
How we learn about the interior of the Sun:
Mathematical models
Sun Quakes:
compare observations with models made from T, P, density
Solar Neutrinos
