THE SUN

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THE SUN

• The star we see by day

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Goals

• Summarize the overall properties of the Sun.
• What are the different parts of the Sun?
• Where does the light we see come from?
• The scientific method solar neutrinos.

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The Sun, Our Star

• The Sun is an average star.
• From the Sun, we base our understanding of all
  stars in the Universe.
• No solid surface.

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Vital Statistics

• Radius 100 x Earth (696,000 km)
• Mass 300,000 x Earth (1.99 x 1030 kg)
• Surface temp 5,800 K
• Core temp 15,000,000 K
• Luminosity 4 x 1026 Watts
• Solar Day
• 24.9 Earth days (equator)
• 29.8 Earth days (poles)

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Interior Properties

• Core 20 x density of iron
• Surface 10,000 x less dense than air
• Average density Jupiter
• Core 15,000,000 K
• Surface 5800 K

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Solar Interior

• Core
• Only place with fusion
• Radiation Zone
• Transparent
• Convections Zone
• Boiling hot

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In The Core

• Density 20 x density of Iron
• Temperature 15,000,000 K
• Hydrogen atoms fuse together.
• Create Helium atoms.

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Nuclear Fusion

• 4H ? He
• The mass of 4 H nuclei (4 protons)
• 4 x (1.6726 x10-27 kg) 6.690 x 10-27 kg
• The mass of He nuclei 6.643 x 10-27 kg
• Where does the extra 4.7 x 10-29 kg go?
• ENERGY! ? E mc2
• E (4.7 x 10-29 kg ) x (3.0 x 108 m/s)2
• E hc/l ? l 4.6 x 10-14 m (gamma rays)
• So 4H ? He light!

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Convection

• A pot of boiling water
• Hot material rises.
• Cooler material sinks.
• The energy from the pots hot bottom is
  physically carried by the convection cells in the
  water to the surface.
• Same for the Sun.

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Solar Cross-Section

• Progressively smaller convection cells carry the
  energy towards surface.
• See tops of these cells as granules.

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The Photosphere

• This is the origin of the 5,800 K thermal
  radiation we see.
• l k/T k/(5800 K) ? l 480 nm (visible
  light)
• This is the light we see.
• Thats why we see this as the surface.

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The Sun
Courtesy of NOAO/AURA
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The Chromosphere

• Hydrogen most common.
• Brightest hydrogen line Ha.
• Chromosphere color

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Ha Sun
Photo by Big Bear Solar Observatory
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Prominences
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Corona

• The hot, low density, gas at this altitude emits
  the radiation we see as the Corona.
• 1,000,000 km
• But corona very faint compared to photosphere.

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Solar Wind

• At and above the corona
• Gas is very hot
• Very energetic
• Like steam above our boiling pot of water, the
  gas evaporates.
• Wind passes out through Coronal Holes
• Solar Wind carries away a million tons of Suns
  mass each second!
• Only 0.1 of total Suns mass in last 4.6 billion
  years.

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Sunspots

• 11-year sunspot cycle.
• Center Umbra 4500 K
• Edge Penumbra 5500 K
• Photosphere 5800 K

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Magnetic fields and Sunspots

• At kinks, disruption in convection cells.
• Sunspots form.

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Magnetic fields and Sunspots

• Where magnetic fields pop out of Sun, form
  sunspots.
• Sunspots come in pairs.

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Solar Cycle

• Increase in solar wind activity
• - Coronal Mass Ejections
• Increase in Auroral displays on Earth
• Increase in disruptions on and around Earth.

Courtesy of SOHO/LASCO/EIT consortium.
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Aurora

• The solar wind
• passes out
• through the
• Solar System.
• Consists of electrons, protons and other charged
  particles stripped from the Suns surface.
• When charged particles and magnetic fields
  interact light!

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2003 CME
Oklahoma 10/29/2003
Credit E. Woldt
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Solar Neutrino Problem

• We observe
• Suns luminosity (total light radiated).
• We hypothesize
• 4H ? He light neutrinos
• We can test
• Observe number neutrinos reaching Earth
• Does our test agree with hypothesis?
• No

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What to Do?

• For 30 years
• Theorists certain of nuclear reaction.
• Observers positive of observations.
• Detected only 1/3 the hypothesized neutrinos.
• What to do?

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Neutrino Flavors

• 3 types of neutrinos
• Electron neutrino
• Tau neutrino
• Muon neutrino
• Nuclear reactions produce only electron neutrino.
• Previous detectors only detected electron
  neutrinos.

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Neutrino Fluctuations

• New detector (2002) gives number of all three
  flavors.
• Total number agrees with number predicted in core
  of Sun.
• Conclusion
• Nuclear hypothesis is correct.
• Neutrinos change flavor.
• Neutrinos have mass (used to be thought
  massless).
• Problem solved ? new science discovered.

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Homework 6

• Due Tuesday 2/3
• Read Exoplanet articles.
• (Homework is to read the articles and website.)
• Website is http//www.howstuffworks.com/planet-hu
  nting2.htm