I.The Solar Spectrum : Sun’s composition and surface temperature II.Sun’s Interior: Energy source, energy transport, structure, helioseismology. III.Sun’s Atmosphere: Photosphere, chromosphere, corona IV.Solar Activity: Sunspots, solar magnetism, solar cycle, prominences and flares. Outline of The Sun (Ch. 10) (Not exactly like the book)

I. Solar Spectrum: Composition and Surface Temperature

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I. Solar Spectrum: How do we know the composition of the Sun?

What type of Spectrum is this?

How do we know this? Surface Temperature: approximately 6,000 K

I.The Solar Spectrum : Sun’s composition and surface temperature II.Sun’s Interior: Energy source, energy transport, structure, helioseismology. III.Sun’s Atmosphere: Photosphere, chromosphere, corona IV.Solar Activity: Sunspots, solar magnetism, solar cycle, prominences and flares. Outline of The Sun (Ch. 10)

What is the source of the Sun’s energy? a) Chemical reactions b) Gravitational contraction c) Nuclear fission (like in nuclear power plants) d) Nuclear fusion Question 1

Why does the Sun shine?

Is it on FIRE? Fuel Rate of burning that fuel

Is it on FIRE? Luminosity ~ 10,000 years Chemical Energy Content

Is it on FIRE? … NO! Luminosity ~ 10,000 years Chemical Energy Content

Is it CONTRACTING?

Luminosity Gravitational Potential Energy Is it CONTRACTING? ~ 25 million years

Luminosity Gravitational Potential Energy Is it CONTRACTING? … NO! ~ 25 million years

E = mc 2 - Einstein, 1905

Is it powered by NUCLEAR ENERGY? Luminosity ~ 10 billion years Nuclear Potential Energy (core)

Is it powered by NUCLEAR ENERGY? … YES! Luminosity ~ 10 billion years Nuclear Potential Energy (core)

What is the source of the Sun’s energy? a) Chemical reactions b) Gravitational contraction c) Nuclear fission (like in nuclear power plants) d) Nuclear fusion Question 1

Fission Big nucleus splits into smaller pieces (Nuclear power plants) Fusion Small nuclei stick together to make a bigger one (Sun, stars)

4 protons  one Helium nucleus + Energy Hydrogen Fusion into Helium in the Sun’s Core

4 protons  one helium nucleus + Energy The mass of the four protons is higher than that of the helium nucleus where did the missing mass go? Hydrogen Fusion into Helium in the Sun’s Core

4 protons  one helium nucleus + Energy The mass of the four protons is higher than that of the helium nucleus where did the missing mass go? The mass became energy, and E=mc 2 so a little mass can produce a lot of energy Hydrogen Fusion into Helium in the Sun’s Core

Proton-proton chain is how hydrogen fuses into helium in Sun

Sun’s interior

Core: Energy generated by nuclear fusion

Radiation Zone: Energy transported upward by photons

Convection Zone: Energy transported upward by rising hot gas

In the Sun, gravity is balanced by outward pressure (due to the outflow of energy)

Solar Thermostat Temperature Restored Temperature Decreases Fusion Rate Decreases Core compresses

Solar Thermostat Temperature Restored Temperature Increases Fusion Rate Increases Core expands

Helioseismology By studying the motion of the Sun’s surface we can learn about its interior in a similar way to the study of Earthquakes.

What have we learned? How does the solar thermostat work? There is a equilibrium between gravity and energy outflow……. How does the energy from fusion get out of the Sun? Energy is produces in the core by nuclear fusion and it gets radiated outward. The convection zone carries energy the rest of the way to the photosphere, where it is radiated into space as sunlight. How do we know what is happening inside the Sun? Helioseismology and other techniques

I.The Solar Spectrum : Sun’s composition and surface temperature II.Sun’s Interior: Energy source, energy transport, structure, helioseismology. III.Sun’s Atmosphere: Photosphere, chromosphere, corona IV.Solar Activity: Sunspots, solar magnetism, solar cycle, prominences and flares. Outline of The Sun (Ch. 10)

Photosphere: Visible surface of Sun T ~ 6,000 K

Chromosphere: Middle layer of solar atmosphere

Corona: Outermost layer of solar atmosphere

Solar Granulation in the Photosphere

Convection (rising hot gas) takes energy to surface

Cloud tops on Earth produced by convection: warm air rises

Sunspots

Sunspots and Solar Rotation

Why do sunspots look dark? a) They are dark clouds b) They are smoke from the Sun’s interior c) They are cooler than the rest of the Sun’s surface d) None of the above Question

Why do sunspots look dark? a) They are dark clouds b) They are smoke from the Sun’s interior c) They are cooler than the rest of the Sun’s surface d) None of the above Question

Loops trace magnetic field lines

Blackbody radiation: The hotter the brighter The hotter the bluer Why do sunspots look dark? They are cooler than the rest of the Sun’s surface Are they redder? Review from Ch 5

Sunspots

Visible during a total solar eclipse Solar Chromosphere

Visible during a total solar eclipse Solar Corona

Coronal mass ejections send bursts of energetic charged particles out through the solar system

I.The Solar Spectrum : Sun’s composition and surface temperature II.Sun’s Interior: Energy source, energy transport, structure, helioseismology. III.Sun’s Atmosphere: Photosphere, chromosphere, corona IV.Solar Activity: Sunspots, solar magnetism, solar cycle, prominences and flares. Outline of The Sun (Ch. 10)

I.Sunspots: main indicator II.Prominences and flares: also indicators of solar activity III.Solar cycle: 11-year cycle IV. Solar Activity

Charged particles streaming from Sun can disrupt electrical power grid and can disable communications satellites

Energetic particles high in Earth’s atmosphere cause auroras (aka Northern Lights)

How does solar activity affect humans? Bursts of charged particles ejected from the Sun during periods of high solar activity can hamper radio communications,disrupt electrical power generation,and damage orbiting satellites. Solar activity can also have a strong impact on Earth’s weather

Sunspot numbers and temperature on Earth: During the mid-to-late 1600s records indicate a very cold period on Earth