copyright © 2012 pearson education, inc. radius: 6.9 10 8 m (109 times earth) mass: 2 10 30 kg...

Copyright © 2012 Pearson Education, Inc.

Radius:

6.9 108 m

(109 times Earth)

Mass:

2 1030 kg

(300,000 Earths)

Luminosity:

3.8 1026 watts

Our Star – The Sun


The Sun

• Why does the Sun shine?

• What is the Sun’s structure?

• What is the 11-year solar cycle?


Why does the Sun shine?


Is it on FIRE?


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?


Is it CONTRACTING?

Luminosity

Gravitational Potential Energy~ 25 million years


Is it CONTRACTING? … NO!

Luminosity

Gravitational Potential Energy~ 25 million years


ALL STARS are powered by NUCLEAR ENERGY!

Luminosity~ 10 billion years

Nuclear Potential Energy (core)

E = mc2

—Einstein, 1905


Nuclear Fusion in the Sun(and All stars)


Weight of upper layers compresses lower layers.


Gravitational equilibrium:Gravity pulling in balances pressure pushing out.

Energy balance:Thermal energy released by fusion in core balances radiative energy lost from surface.


Gravitational contraction…

provided energy that heated the core as the Sun was forming.

Contraction stopped when fusion started replacing the energy radiated into space.


How does nuclear fusion occur in the Sun?


Fission

Big nucleus splits into smaller pieces.

(Nuclear power plants)

Fusion

Small nuclei stick together to make a bigger one.

(Sun, stars)


High temperatures enable nuclear fusion to happen in the core.


The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus.

The new He nucleus is less massive than the original 4 Hydrogen atoms.


Proton–proton chain is how hydrogen fuses into helium in the Sun.


IN4 protons

OUT4He nucleus

2 gamma rays2 positrons2 neutrinos

Total mass is 0.7% lower.


Thought Question

What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?

A. The core would expand and heat up slightly.B. The core would expand and cool.C. The Sun would blow up like a hydrogen bomb.


Solar Thermostat

Decline in core temperature causes fusion rate to drop, so core contracts and heats up.

Rise in core temperature causes fusion rate to rise, so core expands and cools down.


How does the energy from fusion get out of the Sun?


Energy gradually leaks out of the radiation zone in the form of randomly bouncing photons.


Solar Structure and Solar Activity


The Sun goes through periods of relative activity and inactivity (X-ray images)


The Sun’s interior has three layers:(1) core(2) radiative zone (3) convective zone

Energy generated in the core of the Sun propagates outward through these different layers, and finally, through the atmosphere of the Sun. This process takes tens of thousands of years or more.


The Sun’s atmosphere also has three layers…

• Photosphere - the layer we see, 5800 K

• Chromosphere - the red layer observed using a hydrogen filter, 10,000 K

• Corona - the incredibly thin outer atmosphere, 1,000,000 K


The photosphere is the visible layer of the

SunGranulation caused by convection

http://www.whfreeman.com/universe6e - Seething Granules around a Sun Spot


Sunspots are the most well known feature in the photosphere. Monitoring sunspots reveals the

Sun’s rotation.

http://www.whfreeman.com/universe6e - the motion of a small sun spot


The movement of

sunspots reveals that the Sun’s

rotation takes about …

4 weeks


Maximum number

Minimum number

The annual change in numbers of sunspots reveals that the Sun experiences an 11-year Sun Spot cycle


Magnetic field lines connect sunspots on the Sun’s photosphere


Solar magnetic fields also create other atmospheric phenomena

• prominences

• solar flares


The corona, the outermost part of the Sun’s atmosphere, is characterized by its high

temperature and low density

The Sun also ejects a stream of charged particles into space known as the solar wind


Solar magnetic fields also create other atmospheric phenomena

• prominences

• solar flares• coronal mass ejections

(CMEs)


http://www.spaceweather.com/

http://www.spaceweather.com/images2002/18mar02/cme_c3_big.gif


The most powerful solar flare in 14 years, .. erupted from sunspot 486 in late October of 2003. The explosion hurled a coronal mass ejection almost directly toward Earth, which triggered bright auroras when it arrived on Earth.


The Earth’s magnetic field is caused by movement of material in Earth’s interior


Sun’s Magnetic Field Effects The Earth


The Earth’s magnetic field produces a magnetosphere that deflects and traps

particles from the solar wind protecting Earth


Relevance of Earth’s protective magnetosphere

• Protects against Solar Flares - violent explosions on the Sun releasing large burst of charged particles into the solar system

• Protects against Solar Wind - dangerous stream of charged particles constantly coming from the Sun

• Northern Lights (Aurora Borealis) – Caused by the solar wind interacting with the

magnetosphere.


Northern Lights (Aurora Borealis)

As the charged particles from the Sun interact with the magnetic field around Earth, the particles collide with the nitrogen and oxygen atoms in the atmosphere and excite those atoms to emit light

See Mastering Astro animation


Aurora as seen from space

copyright © 2012 pearson education, inc. radius: 6.9 10 8 m (109 times earth) mass: 2 10 30 kg...

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