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Chapter 10. Our Star. Hydrostatic Equilibrium or Gravitational Equilibrium. The outward pressure force balances the inward gravitational force everywhere inside the Sun. Gravitational Equilibrium in the Sun. The Sun’s Properties. The Sun's Atmosphere.
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Chapter 10 Our Star
Hydrostatic Equilibrium or Gravitational Equilibrium • The outward pressure force balances the inward gravitational force everywhere inside the Sun.
The Sun's Atmosphere • Photosphere - "sphere of light", the visible surface of the Sun • Chromosphere - "sphere of color", visible during solar eclipses • Corona - the Sun's outermost atmosphere. The outflow of gas in this region is called the solar wind, which is protons and electrons that have escaped the Sun's gravity.
Auroras are caused by the solar wind. • Solar wind is an outward flow of fast- moving charged particles (mostly protons & electrons)
The Sun's Interior • Thermonuclear core - the central region of Sun where fusion takes place due to high temperatures and pressures. • Radiation zone - a region inside a star where energy is transported outward by the movement of photons (radiation). • Convection zone - a layer inside a star where energy is transported outward by means of heat flow through the gasses of the star (convection).
What makes the Sun shine? • Thermonuclear fusion at the Sun's core is the source of the Sun's energy. 4 Hydrogen ---------> 1 Helium + Light Atoms (fusion) Atom
Mass loss? 4 1 hydrogen = 6.693 10-27 kg - 1 helium = 6.645 10-27 kg ---------------------------------------------- Mass loss = 0.048 10-27 kg The missing mass is converted to pure energy ( i.e. light ) By Einstein’s energy/mass equation. E = mc2
Mass can be transformed into light. This occurs during fusion. Light be transformed into matter. This occurs in pair production. These are results from Einstein’s theory of Special Relativity. What does this mean?
For one hydrogen-to-helium fusion event, E = 4.3 x 10-12 Joules This is a tiny number by itself , but when multiplied by the vast number of hydrogen atoms undergoing fusion and considering the rate of fusion in the Sun, the total power released is equivalent to exploding 100 billion- 1 megaton H-bombs per second! Our sunshine has a violent birth.
Helioseismology- Understanding the Sun’s Interior Modes of vibration • Vibrations on the surface of the Sun can be detected by Doppler shifts Falling Gas (Red) Rising Gas (Blue)
The Neutrino Problem Standard solar model is the generally accepted theory of solar energy production. • The model predicts that billions of neutrinos per second flow from the Sun. • Neutrinos react very little with ordinary matter so detecting them is difficult. • Neutrino telescopes indicate that only 1/3 of the neutrinos predicted by theory are “seen.” Web
Solar Neutrino “Telescopes” Solar Neutrino detector in South Dakota. Cl nuclei would turn into Ar nuclei when they captured solar neutrinos Super –Kamiokande experiment in Japan is one of the world’s latest neutrino detectors.
Convection Transports Energy Outward Convection Cell
Magnetic Field Lines Lines closer together represent stronger magnetic fields Charged particles spiral along field lines Compass needles align with the magnetic field lines
Solar Prominence - a flame-like protrusion seen near the limb of the Sun and extending into the solar corona. These follow magnetic field lines. • Solar Flare – Huge and sudden release of energy on the solar surface, probably caused when energy stored in magnetic fields is suddenly released.
Sun in X-Ray Corona
Sunspot Cycle • The rotation rate varies from once every 25 days to once every 30 days. • This differential rotation twists the magnetic field lines. • This causes the number of sunspots to vary over an 11 year period.
Solar Cycle • A 22 - year period that is needed for both the average number of spots and the Sun’s magnetic field polarity to repeat themselves. The Sun’s polarity reverses on each new 11-year sunspot cycle.
Magnetic Field lines become distorted due to the Sun’s Differential Rotation
Simmary of Surface Features • Granules - convection features about 1000 kilometers in diameter seen constantly in the solar photosphere. • Sunspot - a temporary cool region in the solar photosphere created by protruding magnetic fields. • Prominence - a flamelike protrusion seen near the limb of the Sun and extending into the solar corona.
