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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Scientific Method

• How do we know this stuff?
• Three examples
• Fusion in the core (core temperature).
• Different zones in interior.
• Solar activity and Earth

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1. The Core

• Scientific Method
• Observations
• Make hypothesis (a model)
• Models make predictions
• Test predictions
• Compare results of predictions with observations
• Revise model if necessary.

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Testing the Core

• Observe Suns
• Mass (how?)
• Composition (how?)
• Radius
• Use physics to make a model Sun.
• Predict
• Surface temp/density (how do you test?)
• Surface Luminosity (how do you test?)
• Core temp/density ? Fusion Rate ? neutrino rate
  (test?)

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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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2. Helioseismology

• Continuous monitoring of Sun.
• Ground based observatories
• One spacecraft (SOHO)
• Surface of the Sun is ringing
• Sound waves cross the the solar interior and
  reflect off of the surface (photosphere).

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Solar Interior

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

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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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3. Solar Activity and Earth

• Is there a connection between Solar Activity and
  Earths Climate?
• Observation
• Little Ice Age
• Maunder Minimum

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What is Solar Activity?

• Sunspots
• Magnetic Fields
• Coronal Mass Ejections
• Solar Wind
• Magnetic Storms
• Aurora
• Other effects?

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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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Prominences
Hot low density gas emission lines
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Corona and Solar Wind

• Hot, low density, gas emits the radiation we see
  as the Corona 1,000,000 K
• Solar Wind Like steam above our boiling pot of
  water, the gas evaporates.
• 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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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.
• Magnetic fields herd charged particles into
  atmosphere at poles.
• Charged particles excite electrons in atoms. ?
  Light!

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2003 CME
Oklahoma 10/29/2003
Credit E. Woldt
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Homework 7

• Due Monday 30-Jan, Read Exoplanet articles plus
  the website
• http//www.howstuffworks.com/planet-hunting2.htm
• Why do we believe there are planets around other
  stars? How have we detected them?