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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
The photosphere is
the visible layer of the
SunGranulation caused by convection
Granulation caused by convection
Sunspots are the most well
known feature on the 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-Check1: 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.
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