Docstoc

The Sun

Document Sample
The Sun Powered By Docstoc
					   THE SUN




The star we see by day




                         7
        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.




                                        7
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

                        7
          Scientific Method
• How do we know this stuff?
• Three examples:
  – Fusion in the core (core temperature).
  – Different zones in interior.
  – Solar activity and Earth




                                             7
                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.




                                                          7
            Testing the Core
• Observe Sun’s:
  – 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?)


                                                      7
                  In The Core

• Density = 20
  x density of
  Iron
• Temperature
  = 15,000,000
  K
• Hydrogen
  atoms fuse
  together.
• Create Helium
  atoms.
                                7
           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).
                                7
 Solar Interior
• Core
  – Only place with
    fusion
• Radiation Zone
  – Transparent
• Convections Zone
  – Boiling hot




                      7
                Convection
• A pot of boiling water:
• Hot material rises.
• Cooler material sinks.
• The energy from the
  pot’s hot bottom is
  physically carried by
  the convection cells in
  the water to the
  surface.
• Same for the Sun.

                             7
Solar Cross-Section




        • Progressively smaller
          convection cells
          carry the energy
          towards surface.
        • See tops of these
          cells as granules.7
         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.
• That’s why we see this as the surface.




                                         7
   3. Solar Activity and Earth
• Is there a connection between Solar
  Activity and Earth’s Climate?
• Observation:
  – Little Ice Age
  – Maunder Minimum




                                        7
       What is Solar Activity?
•   Sunspots
•   Magnetic Fields
•   Coronal Mass Ejections
•   Solar Wind
•   Magnetic Storms
•   Aurora
•   Other effects?


                                 7
•   11-year sunspot cycle.
•   Center – Umbra: 4500 K
•   Edge – Penumbra: 5500 K
                              Sunspots
•   Photosphere: 5800 K




                                         7
     Magnetic fields and Sunspots




• At kinks, disruption in convection cells.
• Sunspots form.
                                              7
Magnetic fields and Sunspots
                    • Where
                      magnetic
                      fields “pop
                      out” of Sun,
                      form
                      sunspots.
                    • Sunspots
                      come in
                      pairs.


                               7
               Prominences




Hot low density gas = emission lines   7
7
      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 Sun’s mass
  each second!
• Only 0.1% of total Sun’s mass in last 4.6
  billion years.

                                          7
7
                                         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.
                                                       7
  Aurora

• The solar wind
  passes out
  through the
  Solar System.
• Consists of electrons, protons and other charged
  particles stripped from the Sun’s surface.
• Magnetic fields herd charged particles into
  atmosphere at poles.
• Charged particles excite electrons in atoms.  Light!
                                                    7
7
7
                   2003 CME




                              Oklahoma 10/29/2003

Credit: E. Woldt                                    7
           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?



                                         7

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:4
posted:2/17/2012
language:
pages:27