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 Sun 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 = mc 2 4H  He + energy H YDROGEN F USION

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 neutrinos are released every second Current neutrino detectors on Earth watch for collisions between perchloroethylene cleaning fluid (C 2 Cl 4 ) 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.