Download Lecture07

ASTR 1102-002
2008 Fall Semester
Joel E. Tohline, Alumni Professor
Office: 247 Nicholson Hall
[Slides from Lecture07]
Chapter 16: Our Star, the Sun
Chapter Overview
• The Sun’s Surface & Atmosphere
– 16-5: Why the gaseous Sun appears to have a sharp
outer edge
– 16-6: Why the upper regions of the solar atmosphere
have an emission spectrum
– 16-7: The relationship between the Sun’s corona and
the solar wind
– 16-8: The nature of sunspots
– 16-9: The connection between sunspots and the
Sun’s magnetic field
– 16-10: How magnetic reconnection can power
immense solar eruptions
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
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.
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,
but first, let’s skim through the material in sections
16-5 through 16-10.
Figure 16-7
16-5: The Sun’s Photosphere
Figure 16-9
Granulation of the Photosphere
Figure 16-9
Granulation of the Photosphere
A high-resolution photograph of the Sun’s surface reveals a blotchy pattern called
granulation.
Figure 16-9
Granulation of the Photosphere
A high-resolution photograph of the Sun’s surface reveals a blotchy pattern called
granulation; this is evidence of heat convection (the surface is boiling).
16-8: Sunspots
Figure 16-7
(low-temperature regions in the photosphere)
16-8: Sunspots
Figure 16-17
(Tracking the Sun’s Rotation)
16-8: Sunspots
(Tracking the Sun’s Rotation)
Figure 16-17
The Sun rotates
once in about
4 weeks.
16-8: Sunspots
(The Sunspot Cycle)
Figure 16-18
16-8: Sunspots
(The Sunspot Cycle)
Figure 16-18
The number of sunspots on the Sun varies with a period
of about 11 years; most recent maximum in year 2000.
Figure 16-11
16-6: The Sun’s Chromosphere
16-7: The Solar Corona
Figure 16-13
(visible light)
16-7: The Solar Corona
Figure 16-15
(ultraviolet light)
Figures 16-27 & 16-28
16-10: Coronal Prominences
16-9: Sun’s Magnetic Field
• The Sun contains a magnetic field with a fairly
complex structure
• “Coronal loops” (see Fig. 16-25) and “prominences”
often outline the magnetic field’s complex
structure
• Sunspots appear to be associated with regions
on the Sun’s surface where the magnetic field is
especially strong
• The north and south magnetic poles of the Sun
reverse every 11 years!
16-9: Sun’s Magnetic Field
• The Sun contains a magnetic field with a fairly
complex structure
• “Coronal loops” (see Fig. 16-25) and “prominences”
often outline the magnetic field’s complex
structure
• Sunspots appear to be associated with regions
on the Sun’s surface where the magnetic field is
especially strong
• The north and south magnetic poles of the Sun
reverse every 11 years!
NOTE (see §9-4): The Earth’s own magnetic field reverses direction on an irregular
schedule ranging from tens of thousands to hundreds of thousands of years!
Relevance to Other Stars…
• If the Sun is a “typical” star, think about
how all these surface phenomena may be
relevant to our studies of all other stars
– Intrinsic brightness can be variable
– Mass of a star may decrease over time
– Magnetic fields may be important
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
– 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!