Download Foundation 1 - Discovering Astronomy

Chapter 9
Our Star, the Sun
What do you think?
• What is the surface of the Sun like?
• Does the Sun rotate?
• What makes the Sun shine?
Outer Layers of the Sun’s
Atmosphere
• Photosphere - the 5800 K layer we see
• Chromosphere - the red layer observed
using a hydrogen filter at a million degrees
• Corona - the incredibly thin outer
atmosphere at millions of degrees
Granulation caused by convection
The
photosphere is
the visible
layer of the
Sun
Sunspots are
the most well
known
feature on the
Granulation caused by convection
photosphere
Above the photosphere, the chromosphere is
characterized by spikes of gas called spicules
Supergranuals surrounded by spicules
The corona ejects some of its
mass into space as the solar wind
Monitoring sunspots reveals the
solar cycle and the Sun’s rotation
The daily
movement of
sunspots
reveals that
the Sun’s
rotation takes
about 4
weeks
The annual change in numbers of sunspots reveals
that the Sun experiences an 11-year solar cycle
Maximum
number
Minimum
number
The cyclical change in the latitude of sunspots also
reveals that the Sun experiences an 11-year solar cycle
The Sun’s magnetic fields create sunspots
Zeeman effect - spectral
lines split in regions of high
magnetic fields
Magnetic field lines connect sunspots on the Sun’s photosphere
Babcock’s magnetic dynamo is one possible explanation of the
sunspot cycle where magnetic field lines become complexly
entangled after many solar rotations
Solar magnetic fields also create
other atmospheric phenomena
• plages
• filaments
Solar magnetic fields also create
other atmospheric phenomena
• plages
• filaments
• prominences
Solar magnetic fields also create
other atmospheric phenomena
•
•
•
•
plages
filaments
prominences
solar flares
Solar magnetic fields also create
other atmospheric phenomena
•
•
•
•
•
plages
filaments
prominences
solar flares
coronal holes
Solar magnetic fields also create
other atmospheric phenomena
•
•
•
•
plages
filaments
prominences
solar flares
• coronal holes
• coronal mass
ejections
(CMEs)
Thermonuclear reactions in the core
of the Sun produce its energy
At extremely high temperatures and pressures, 4 Hydrogen
atoms can combine to make 1 Helium atom and release energy
in the process according to E = mc2
4H  He + energy
HYDROGEN FUSION
Solar models
describe how
energy escapes
from the Sun’s
core through
the:
(1) core,
(2) radiative
zone, and the
(3) convective
zone
Helioseismology is the study of solar
vibrations in order to determine the
detailed interior structure of the Sun
Mystery of the Missing Neutrinos
• Current models of the solar interior predict
that 1038 neutrinos are released every second
• Current neutrino detectors on Earth watch for
collisions between perchloroethylene
cleaning fluid (C2Cl4) and neutrinos which
produces radioactive argon.
• Only 1/3 of the expected neutrinos from the
Sun are being detected
• Astronomers do not know why this occurs
What did you think?
• What is the surface of the Sun like?
The photosphere is composed of hot, churning gases.
There is no solid or liquid region in the Sun.
• Does the Sun rotate?
The Sun’s surface rotates differentially. The rate varies
between once every 25 and once every 35 days.
• What makes the Sun shine?
Thermonuclear fusion at the Sun’s core is the source of the
Sun’s energy.
Self-Check
1: Name the three layers of the solar atmosphere and describe
and the relative temperatures and densities in each.
2: Describe flares, spicules, granules, prominences, and sunspots
and identify the layer in the solar atmosphere in which is
found.
3: Indicate what is observed in helioseismology and explain its
value in investigating the Sun.
4: Explain the nuclear fusion process that is the principal energy
source in the solar interior and describe the physical
conditions required for this process to proceed effectively.
5: List and describe the two primary mechanisms for energy
transport in stellar interiors and indicate in which regions of
the solar interior, if any, each is dominant.