Why is the Sun Important to Us? LAST TIME - Formation of ...neffj.people.cofc.edu/ASTR129/Notes/lec14.pdf · 1! Lec 14: 12 OCT 11 Chapter 16 - The SUN! LAST TIME - Formation of the

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Lec 14: 12 OCT 11 Chapter 16 - The SUN LAST TIME - Formation of the Solar System TODAY - The “Quiet” Sun

•  Why is it important? What can it tell us about other stars, planetary systems, etc.

•  Why does it “shine”? •  What is it made of? Internal Structure.

How do we know? In Lab This Week - The “Active” Sun

Next: “Debris” in the Solar System Read Chapter 14-9, 14-10, and 15 for next week!

Why is the Sun Important to Us? •  contains nearly all the mass

in the solar system; everything in s.s. orbits Sun

•  provides energy (heat) through electromagnetic radiation ==>Source of life

•  produces particles and magnetic field that interact with planetary magnetospheres, atmospheres, and surfaces

Next semester: “Rosetta Stone” to understand stars

Some Facts About the Sun •  ordinary star: middle age, middle size, middle

temperature, middle brightness, etc. One of 100 billion in our galaxy!

•  not a binary •  huge, nearly constant output of energy; we only

receive a tiny portion of it

4 x 1026 Watts

1365 W/m2 rotation period: 24 days (at equator)

Almost all of the energy used on the Earth comes originally from the Sun

How Does The Sun Generate Energy? How Much Energy Does the Sun Produce? •  Sun is in a steady-state and in balance

–  not varying (much) –  not expanding or contracting (much)

•  And it has been for a very long time (4.6 billion years)

Energy Emitted = Energy Produced

Luminosity = 4 x 1026 Watts

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•  Remember how solar system formed. Most of material ended up in the center.

•  Gravitational collapse -> temperature increases.

•  Once begun, the fusion reactions generated energy which provided an outward pressure.

•  This pressure perfectly balances the inward force of gravity at all levels

•  This balance is called hydrostatic equilibrium

What Keeps It From Blowing Itself Apart? How Does it Do It? •  gravitational contraction provided initial heat

source (along with accretion energy) •  could only “fuel” present output of Sun for

~100,000 years! •  of all known energy sources, only FUSION can

provide this energy at this rate for > 5 billion years

•  fusion (of light nuclei into heavier nuclei) requires high temperature and high pressure to begin and to sustain; why?

The Sun’s energy is produced by hydrogen fusion, a sequence of thermonuclear reactions in which four

hydrogen nuclei combine to produce a single helium nucleus. This is known as the proton-proton chain.

The net effect is:���

4H 1He + Energy

•  The mass of the 4 Hydrogen nuclei is greater than the mass of the 1 Helium nucleus

•  The mass difference is converted to energy.

E = mc2 600 million tons of Hydrogen to Helium per second for 10 billion years

•  The Sun’s interior is opaque, we can not see directly into it •  We can construct mathematical computer models of it.

•  grids of temperature, pressure, & density vs. depth •  these values are calculated using known laws of physics •  they are tested against the Sun’s observable quantities

•  We can indirectly measure sound waves moving through the interior

•  these can be used to probe conditions in the interior of the Sun

“Observing” the Solar Interior •  Helioseismology is the

study of how the Sun’s “surface” vibrates up and down

•  These vibrations have been used to infer pressures, densities, chemical compositions, and rotation rates within the Sun

•  There might be another way to see all the way into the core … neutrinos!

Helioseismology

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Neutrinos •  produced in fusion reactions •  “little neutral” particles;

energetic (fast) •  don’t interact with atoms,

molecules, nuclei, very well •  therefore fly straight out of

the Sun in all directions •  almost impossible to stop, but

a tiny fraction can be caught in a detector

•  only about 1/3 as many as expected!

•  Core •  1.5 x 107 K 0.25 R

•  Radiation Zone •  > 2 x 106 K 0.70 R

•  Convection Zone –  < 2 x 106 K 0.85 R

•  Photosphere •  5.8 x 103 K 400 km thick

•  Chromosphere •  1– 5 x 104 K 2,500 km thick

•  Corona •  2 x 106 K 600,000 km thick

•  Solar Wind •  > 106 K beyond the Kuiper Belt

Layers of the Sun Temperature Depth

Energy Transfer in Sun •  gamma ray photons

produced by fusion in core; neutrinos escape

•  radiative diffusion •  convection zone •  photosphere heated from

below by convection, conduction, radiation

•  light - 1 million years to get out then 8 minutes to Earth

•  heavy elements made in core but don’t mix

Photosphere The visible “surface” of the Sun. But it’s not a solid surface, just the deepest we can see into the solar atmosphere

Convection in the photosphere produces

granules

Solar Magnetic Activity •  Photosphere:

visual sunspots

•  Chromosphere: H-alpha & UV plage & spicules

•  Corona: X-ray loops & streamers flares

•  Solar Wind: charged particles coronal mass ejections

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Sunspots: relatively cool���regions in the photosphere

Sunspots can be used to measure solar rotation

Rotates about once per month, but when it formed it spinned a lot faster!

“Differential Rotation”: equator rotates faster than poles

Sunspots are also regions of intense magnetic field

Strong magnetic field suppresses convection

The Solar Cycle

1992

1996 Minimum Maximum

1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Number of Sunspots

"   11 year cycle of intensity, sunspot number, etc.

"   spots emerge at higher latitude at beginning of cycle; at equator near end of cycle

"   22 year cycle of polarity

The solar “dynamo” is controlled by convection and differential rotation���(but we don’t understand it very well)

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Above photosphere, Temperature INCREASES with height!

Where does energy come from?

•  magnetic field?

•  sound waves?

How does it get deposited into the thin plasma in the outer atmosphere?

We know magnetic field is related to rotation and convection

Chromosphere: Hotter than the Photosphere!

The corona: almost as hot as the core!

Magnetic “Storms” in the Solar Corona

•  A solar flare is a brief eruption of hot, ionized gases from a sunspot group

•  A coronal mass ejection is a much larger eruption that involves immense amounts of gas from the corona

Coronal Mass Ejections

Earth Is Shown For Size Comparison

Earth Magnetic Cloud

Coronal Mass

Ejection SUN

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Coronal Holes Effects of Solar Activity on ���Earth’s Environment

power grids pipelines radio communications

spacecraft health astronaut health airline passenger health

aurorae evolution of life climate???

Correlations between activity and climate are highly suggestive, but what is the mechanism?

Some correlations could be spurious:

Number of Sunspots vs. # of Republicans in US Senate