Sun – chapter 16

Composition, Energy source, Structure, “normal life” changes

Goals & Outcomes• Explain how electromagnetic radiation and astronomical

instruments are used to reveal the properties of stars and galaxies.

• Diagram the process of nuclear fusion.• Learn about some problems astronomers and astrophysicists

are trying to solve, and understand the methods scientists are using to try to solve these problems.

• Develop a sense of what scientists know about the overall universe, its constituents, and our location

• Diagram and explain radiative transport in the Sun. Explain the causes of surface features on the Sun.

Major Sun facts

• What’s a star?– _______________________– ________, so it must ___________________.

Must protect your body if in space!• Which ___________________?

– ____________________________________– Other: O=1%, C=0.4%, Fe=0.14%, N=0.1%,

Si, Mg, Ne, S 0.040.1%.• How do we know these numbers?

Sun’s Age

• Easy to measure: ___________________• Can figure out ______________• __________________ tell us age must be

____________________________• _________________ tell us ___________• What can make the Sun shine so bright for

so long?

Sun

The picture shown to the right is taken using the Hydrogen 3 2 transition (red colored, called H-alpha

• This is discussed on page _________.• ____________________________________• ____________________________________• ____________________________________• Until 1920, ___ idea _____________________.

– _____________________________________• _______________. (Do humans use _______?)• ______________________________________

– (For more details, see figure 14.7 – not on test)

– Every sec: ________tons ___ into ________tons __.– Can do this for a total of _______________ years– How old is Sun. How much time left?

• Review: what’s H atom made of? He atom?

Power Sources and how long Sun could shineSee common misconception__________

Why is fusion difficult for people & Sun?• What is nuclear fusion? What’s in the nucleus?• Why would they be ____________________?

– Fig 14.6, top

• What must happen to ___________________?• _____________ “turns on” when ___________

– Fig 14.6, bottom

• Why ________________________________?• How do you overcome this?• Where are conditions right?

– ____________________________________ water• Humans use more energy than fusion releases,

with current technology. Wait 30 years!

At what temperature does helium fuse with another helium?

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0 1. Also at 15 million K2. Less than 15 million K3. More than 15 million K

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Calif. Elementary School Science Standards for nuclear processes

• From California Science Standards, high school

– Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome the electromagnetic repulsion between the protons

– Students know the energy release per gram of material is much larger in nuclear fusion or fission reactions than in chemical reactions. The change in mass (calculated by E = mc2 ) is small but significant in nuclear reactions.

– Students know the Sun is a typical star and is powered by nuclear reactions, primarily the fusion of hydrogen to form helium.

Structure & evolution of the Sun

• Start with a clicker question.

Star lives – a constant struggleFigure _________, page _______

• Gravity tries to ____________________• Shrinking wins until …• Some source of _____________________

– What is the Sun? (What is any star?)– Big sphere of _________________________.– ____________________________________

_____________________________.• Think of an example of balls of gas in your

everyday life.• What do you do to _________________________

(i.e. _________________________)?

Gravity & Pressure imbalance(pp. __________) Figure 14.8

• If _________________ than gas pressure, what happens?– Gas ___________ and becomes _____ when

it _________________.– Fusion in the core will _________. Star _____

• If ______________________ than gravity, what happens?– Gas ___________ and becomes _____ when

it _____________.– Fusion in the core will _________. Star _____

Review question: Does the mass of the Sun change over its lifetime?

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0 1. Yes2. No

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Review question: How does the mass of the Sun change over its lifetime?

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1. Not at all2. A little bit, but not noticeable3. The Sun’s mass changes noticeably

Sun’s structure – radiation transport

• See figure _______, page ______.• ___________________________

– ______________________ K• ______________ – where energy carried by ______• _______________ – energy carried by ____________• ________________ – ________________________• ______ – ______________________ – see pic above

– How could we see this?• _________________ comes off the Sun.

– _______________________________________.– Causes ____________________ (aurora borealis/australis).– Affect atmospheres, magnetism

Radiation & Convection Zones• Core is hot – thermal emitter• __________________________________

– _____________________________________________• _____________________________________. Figure ___________

– “_________________ photons”• Takes __________________________ to “walk” from core

outside• ___________________________________

– Outer layers are ________________, stuff gets _________– Photons get “_______________”– ______________. _______________. _________________– Movement is visible through ECC scopes!– See figure ____________

• ___________________________– __________________________. Outside temp: _______ K.– Quick review question: how long does it take light to get here

once it leaves the Sun?

Evil scientist magically turns off fusion. Would you notice after 6

minutes?

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0 1. Yes2. No

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Evil scientist magically turns off fusion. Would you notice after 10

minutes?

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0 1. Yes2. No

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The amount of Helium in the Sun is:

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0 1. Increasing2. Decreasing3. Staying the same

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What’s happening to the number of particles in the Sun’s core?

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0 1. Increasing2. Decreasing3. Staying the same

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Slow evolution of the Sun

• What happens to core gas pressure as a result of ________________________________?

• What happens to the core? It _____ and _____.• That causes what?• Balance restored!• What happens to fusion rate?• What happens to the Sun’s luminosity?

Studying Sun’s interior

• Helio__________________________– See figure 14.11– ____________________ tell us about insides– Strongest clues about interior of the Sun– Figure 14.12 shows results

Solar Neutrinos• ________________(turning proton into neutron).

– 3% of Sun’s energy in neutrino form. 97% light.• ________________________________________

– _________________________________________• _________________they interact with stuff

– ___________. See figure 14.14 page 506– 60 billion/cm2/sec. New million ton detectors “see” ___

neutrinos per day. [New versions: looking for dark matter!]

• We saw 1/3 to ___________________from fusion• HUGE puzzle• Solution (May 2001): neutrinos _______________

– ____________________weren’t detectable in past.

Another neutrino detector

• Japanese - Super Kamiokande

• filled with 50,000 tons of water

• 13,000 light detectors(seen on wall)

Link to Earth - spots

• What are the spots?

• Hotter or colder than the rest of the photosphere?

• Like ___________ ______________, they’re _________ _______________

______________________

• ____________________:–_____________________–______________________–___________________ (probably)

• _________ Rotation: figure _____

Solar _____________

• Sunspots go through _________________ – few spots to many back to few.– 2007 “Solar _______________________”– When is the next “Solar maximum”

• Cycle isn’t a perfect clock• Some cycles stronger than others• Figures 14.22 & 14.23• There might be a link to _______________ /

_____. But __________________________.

Summary• We know the Sun fuses based on its age• Fusion energy source & productS• Composition (general)• Why fusion is difficult (repulsion, strong force)• Gravity vs. pressure. How currently balanced?• Different “layers” of Sun, a little about each• Neutrinos – what, where, problem?• Magnetic fields• Solar Cycle – time, observable results• A PUZZLE: north pole is warmer than south pole by

80,000K all the time. (Does not flip when magnetic field does.) Stay tuned.