ASTR 1102-002
2008 Fall Semester
Joel E. Tohline, Alumni Professor
Office: 247 Nicholson Hall
[Slides from Lecture08]
Chapter 16: Our Star, the Sun
Chapter Overview
• The Sun’s Interior
– 16-1: The source of the Sun’s heat and light
– 16-2: How scientists model the Sun’s internal
structure
– 16-3: How the Sun’s vibrations reveal what lies
beneath its glowing surface
– 16-4: How scientists are able to probe the Sun’s
energy-generating core
This is the textbook material on which I will focus.
Figure 16-4
Sun’s Internal Structure
Modeling the Sun’s Interior
1. Hydrostatic Equilibrium
2. Thermal Equilibrium
3. Energy from nuclear fusion (E = mc2)
Modeling the Sun’s Interior
• Hydrostatic Equilibrium
– Gas pressure force (directed outward) balances force
of gravity (directed inward) throughout the interior
– If not balanced, Sun’s structure should change
appreciably in a matter of hours!
Modeling the Sun’s Interior
• Hydrostatic Equilibrium
– Gas pressure force (directed outward) balances force
of gravity (directed inward) throughout the interior
– If not balanced, Sun’s structure should change
appreciably in a matter of hours!
Modeling the Sun’s Interior
• Thermal Equilibrium
– Sun is steadily losing energy at its surface (it’s
shining!); it is trying to “cool off”
– Heat from the Sun’s interior slowly diffuses toward the
surface
– This lost heat can be replenished by slow
gravitational contraction (whenever a gas is
compressed, its temperature rises); this is referred to
as “Kelvin-Helmholtz contraction” (see §16-1)
– If Kelvin-Helmholtz contraction is responsible for
keeping the Sun’s interior hot, the Sun’s structure
should change appreciably on a time scale of ~ 10
million years
Modeling the Sun’s Interior
• Thermal Equilibrium
– Sun is steadily losing energy at its surface (it’s
shining!); it is trying to “cool off”
– Heat from the Sun’s interior slowly diffuses toward the
surface
– This lost heat can be replenished by slow
gravitational contraction (whenever a gas is
compressed, its temperature rises); this is referred to
as “Kelvin-Helmholtz contraction” (see §16-1)
– If Kelvin-Helmholtz contraction is responsible for
keeping the Sun’s interior hot, the Sun’s structure
should change appreciably on a time scale of ~ 10
million years
Modeling the Sun’s Interior
• Thermal Equilibrium
– Sun is steadily losing energy at its surface (it’s
shining!); it is trying to “cool off”
– Heat from the Sun’s interior slowly diffuses toward the
surface
• Radiative diffusion (diffusion of light)
• Convection (“boiling”)
• Timescale: It takes approximately 170,000 years for energy
created at the Sun’s center to travel to and escape from the
surface of the Sun!
Modeling the Sun’s Interior
• Thermal Equilibrium
– Sun is steadily losing energy at its surface (it’s
shining!); it is trying to “cool off”
– Heat from the Sun’s interior slowly diffuses toward the
surface
– This lost heat can be replenished by slow
gravitational contraction (whenever a gas is
compressed, its temperature rises); this is referred to
as “Kelvin-Helmholtz contraction” (see §16-1)
– If Kelvin-Helmholtz contraction is responsible for
keeping the Sun’s interior hot, the Sun’s structure
should change appreciably on a time scale of ~ 10
million years
Modeling the Sun’s Interior
• Thermal Equilibrium
– Sun is steadily losing energy at its surface (it’s
shining!); it is trying to “cool off”
– Heat from the Sun’s interior slowly diffuses toward the
surface
– This lost heat can be replenished by slow
gravitational contraction (whenever a gas is
compressed, its temperature rises); this is referred to
as “Kelvin-Helmholtz contraction” (see §16-1)
– If Kelvin-Helmholtz contraction is responsible for
keeping the Sun’s interior hot, the Sun’s structure
should change appreciably on a time scale of ~ 10
million years
A Problem with Time Scales!
Chemical Elements & Their Isotopes
Courtesy of: http://atom.kaeri.re.kr/
Chemical Elements & Their Isotopes
Hydrogen
Chemical Elements & Their Isotopes
Hydrogen
Chemical Elements & Their Isotopes
Helium
Chemical Elements & Their Isotopes
Helium
Chemical Elements & Their Isotopes
Carbon
Chemical Elements & Their Isotopes
Carbon
Chart of Nuclides
Chart of Nuclides
Chart of Nuclides
Chart of Nuclides
Chart of Nuclides
Chart of Nuclides
Chart of Nuclides
Chart of Nuclides
14
C
Chart of Nuclides
14
6 + 8 = 14
C