Announcements
•Exam 1 Results—average 77%
Grades Histogram
The Sun
• How is energy transported in the
Sun?
• What are sunspots?
• What is the solar neutrino
problem?
Reminder of the Sun’s Structure
Energy Transport: Radiative Diffusion
Energy
in
Hot
Core
proton
electron
Energy
out
Convection
Zone
Radius increasing outward, temperature decreasing
Photons “diffuse” outward, trying to distribute themselves evenly
Energy Transport: Convection
Photosphere
Gas rises & cools
Gas is heated
Gas releases its energy,
Radius
cools & drops
increases,
temperature
decreases
Radiative Zone
Moving outward: T drops, ionization decreases, H- forms
⇒ continuum opacity
Energy Transport: Convection
We can see the convection! The granules are ~1000 km
across.
Fig. 15.14b
Solar convection movie
Concept Question: Convection
Which of these processes is convection?
A) The gas motions that cause astronomical
seeing and mirages
B) A fan blowing air
C) The smell of a chocolate dessert wafting
through your kitchen
Concept Question: Convection
Which of these processes is convection?
A) The gas motions that cause
astronomical seeing and mirages
B) A fan blowing air
C) The smell of a chocolate dessert wafting
through your kitchen
Quiz Question 1: Solar Granules
Which energy transport mechanism leads to the
granulation of the solar surface?
A) Radiative Diffusion
B) Convection
Quiz Question 1: Solar Granules
Which energy transport mechanism leads to the
granulation of the solar surface?
A) Radiative Diffusion
B)Convection
Quiz Question 2: Solar Structure
Which of the following is the correct ordering of layers
of the Sun moving from the center to the outside?
A) corona, radiative zone, core, convective zone
B) convective zone, radiative zone, corona,
photosphere
C) core, radiative zone, photosphere, corona
D) convective zone, radiative zone, corona,
photosphere
Quiz Question 2: Solar Structure
Which of the following is the correct ordering of layers
of the Sun moving from the center to the outside?
A) corona, radiative zone, core, convective zone
B) convective zone, radiative zone, corona,
photosphere
C) core, radiative zone, photosphere, corona
D) convective zone, radiative zone, corona,
photosphere
How do we know so much about the
interior of the Sun?
Fig. 15.09
Fig. 15.10b
•Mathematical models (e.g., gravitational equilibrium,
nuclear physics) with observational constraints (e.g., mass,
composition, energy generation rate)
•Helioseismology (sunquakes):
Sunspots: Magnetic Storms
Fig. 15.15a
Sunspots: Magnetic Fields
Charged particles (electrons) orbit magnetic field lines
N
Plasma and
field lines
are tied
together
S
Small test
magnet, like
in a compass N
S
e-
“Lines of force”, like rubber bands, indicate the alignment and
strength of the magnetic field
Sunspots: Differential Rotation
The Sun has a magnetic field and rotates differentially: a 27
day period at the equator and longer at the poles.
Fig. 15.22
1st SOHO Movie
Sunspots: Temperature
Sunspots appear dark because they are cooler than their
surroundings
Fig. 15.17a&b
Concept Question: Sunspots
If a sunspot were transplanted to the Earth’s surface, from
space it would appear
A) dark and invisible on the night side.
B) bright and would stand out against the surroundings.
Concept Question: Sunspots
If a sunspot were transplanted to the Earth’s surface, from
space it would appear
A) dark and invisible on the night side.
B) bright and would stand out against the
surroundings.
Sunspots are ~4,500 K, whereas the Earths’s surface
is ~300 K.
The Sunspot Cycle
The number of sunspots cycles with a period of 11 years, and
the magnetic polarity of the Sun flips every 22 years, yielding a
total period of 22 years for the cycle.
In the latter
1600’s, there was
a minimum in
sunspot number,
the Maunder
minimum.
Auroras
Coronal mass ejections occur, especially during sunspot
maximum, ejecting charges particles into space. These cause
auroras.
Solar Neutrinos from the PP Chain
Net Result
Detailed Reaction
γ
ep
p
γ
e+
pn
ν
γ
ppn
p
ppn
Key to new particles:
ν = neutrino
γ = gamma ray
e+ = positron
p
ppnn=4He
p
c.f. Fig. 15.7
Detection of Solar Neutrinos
The detection of solar neutrinos is direct evidence
for nuclear reactions in the Sun.
•Neutrinos don’t easily interact with matter: it
takes a light year of lead to stop a typical neutrino
•Neutrino experiments have detected neutrinos
(such as using Cl + ν → Ar)
•Detection rate is only ~1/3 of what it should be
⇒Either our “standard solar model” is
incomplete, or neutrinos can change form
(neutrino oscillations)
Concept Question: Solar Neutrinos
Do as many solar neutrinos pass through your body at
night as during the day?
A) Yes
B) No
Concept Question: Solar Neutrinos
Do as many solar neutrinos pass through your body at
night as during the day?
A)Yes
B) No