Composition of the Sun

1
Composition of the Sun

• Properties of our sun
• Radius 7x109 meters (109 times the radius of the
  Earth)
• Mass 2x1030 kg (333,000 times the mass of the
  Earth)
• Temperature of surface 5780 K (9900º F)
• Temperature of core 15,000,000 K (27,000,000 F)
• Composition
• 71 Hydrogen
• 27 Helium
• 2 heavier elements
• Power output 4x1026 watts

2
Layers of the Sun

• Corona
• Outer atmosphere
• 1 million degrees
• Gas has such low density it is almost invisible
• Can be seen only when photosphere blocked out
• Coronal holes holes of cooler gas
• Chromosphere
• Lower atmosphere
• 4000 K to about 50,000 K

3
Layers of the Sun

• Photosphere
• The visible surface of the Sun
• Temperature about 6000 K
• In this layer, the Suns gases change from
  transparent to opaque.
• Photosphere allows the Sun to retain heat.
• Convection Zone
• Energy from core is slowed in the layer just
  below the photosphere.
• Gases here are cooler and less transparent
• Rising and falling convection currents carry the
  energy to the surface

4
Layers of the Sun

• Radiative Zone
• Just outside the core, energy moves by radiation
  carried by photons.
• Photons travel less than an inch before being
  absorbed.
• Another photon is re-emitted and almost
  immediately reabsorbed.
• This cycle continues until the energy reaches the
  convection zone.
• It takes about 100,000 years for photons to
  travel from the core to the surface.
• Core
• Nuclear fusion supplies the energy in the core
• Density at core more than 100 times that of water
• Although so dense, the whole Sun is gaseous high
  temperatures allow the atoms to stay in a
  constant state of motion

5
How the Sun works

• Hydrostatic Equilibrium
• The balance between outward pressure and inward
  gravity
• Nuclear Fusion
• At high temperatures, hydrogen nuclei fuse to
  make helium and give off energy.
• Hydrogen in the Sun can consist of either one
  proton (1H) or one proton and one neutron (2H).
  (Electrons are lost)
• Helium in the Sun can consist of either two
  protons and one neutron (3He) or two protons and
  two neutrons (4He). (Electrons are lost)

6
How the Sun works

• The Proton-Proton Chain
• First Step
• Two 1H collide and form 2H.
• In the collision, one of the protons becomes a
  neutron by ejecting a positron (e) and a
  neutrino (?)
• 1H 1H ? 2H e ? Energy
• Missing mass converted to energy according to
  Emc2
• Second Step
• The 2H collides with a third 1H to make 3He
• This collision releases a high-energy photon or
  gamma ray (?)
• 1H 2H ? 3He ? Energy
• 3He has a smaller mass than the preceding
  particles, so energy is released. (Emc2)

7
How the Sun works

• Third Step
• Two 3He collide and creates one 4He and two 1H
• 3He 3He ? 4He 1H 1H Energy
• Energy is created from missing mass (Emc2)

8
Neutrinos

• Ejected from the sun during the proton-proton
  chain.
• No electric charge and extremely low mass.
• They pass through anything in their path.
• Trillions of neutrinos pass through a persons
  body every second.
• They are able to travel unfazed through a lead
  barrier a light-year thick.
• Detected when they smash into electrons in water
  tanks and give off a tiny flash of light.

9
Solar Magnetic Activity

• Sunspots
• Most common type of solar magnetic activity
• Large, dark-appearing regions on the Suns
  surface
• Range from a few hundred to many thousand
  kilometers across
• Dark color is due to the fact that they are
  cooler than the surrounding gas
• They are cooler because they contain patches of
  strong magnetic activity

10
Solar Magnetic Activity

• Magnetic field more than 1000 times stronger than
  Earths
• Electrons and other charged particles spiral
  around the field, frozen to it
• Particles forced to follow magnetic field
• Magnetic field slows the ascent of hot gas in the
  convection zone
• Surface cools
• Becomes darker

11
Solar Magnetic Activity

• Prominences
• Huge plumes of glowing gas that jut from the
  lower chromosphere into the corona
• They form where the Suns magnetic field reduces
  heat flow to a region
• They are cooler than the gas around them
• Pressure inside is less than outside
• The hot external gas bottles up the cooler gas
  of the prominence

12
Solar Magnetic Activity

• Solar Flares
• Brief but bright eruptions of hot gas in the
  chromosphere
• Solar flares are not well-understood
• One theory
• The magnetic field near a spot gets twisted by
  gas motions
• Magnetic field gets to a point to where it must
  readjust and whip the gas in that vicinity into a
  new configuration
• The sudden motion heats the gas and it expands
  explosively.
• Some gas escapes and shoots across the solar
  system to Earth