Post on 11-Jan-2016
The Sun
Our Nearest Stellar Neighbor
• Officially known as Sol, as in Solar System.
• Each star in the sky would be referred to as a sun by (hypothetical) inhabitants of the planets that orbit it.
• Like almost all stars, 74% H and 24% He, with trace amounts of other elements (2%).
Vital Statistics
• 93 million miles away,
• 864,000 miles in diameter (about 100 Earths across, and it would hold 1,000,000),
• 4.567 billion years old, using Uranium/Saramium radiometric dating.
• Good for another 5 billion.
fire Fire FIRE!• Not!• There is no fire on the Sun;• A fire of normal combustion with the Sun’s mass
would only last a few thousand years.• The source of the Sun’s energy is nuclear fusion
—similar to the fusion discussed earlier. • The Lawson Criteria hold.
Structure
• Largely due to the fusion process and the energies it produces.
• The core is where the fusion occurs,
• The radiative zone transmits heat to the,
• Convective zone which moves the heat to the Photosphere, the surface of the Sun we see.
Hydrostatic equilibrium
• The balance between the explosive force of the fusion at the center and the crushing gravity of its 2E30kg
• When it fails the Sun will change drastically
Heat Flow
• The core of the Sun is about 15 million degrees.• Using E = mc2, it converts around 6.5 million
tons of H into energy every second!• This is 400 million million million million Watts
of power, +/- 0.07%.• Visible light output varies to a small degree, but
the UV output varies greatly.• Sunspots a measure of that variability.
Outward
• Above the core, the pressure/temperatures aren’t sufficient for fusion, so heat is radiated through a layer of hot gas.
• Eventually, the pressures are low enough for “normal” convective fluid flow, which brings the heat to the surface, or photosphere.
At the Surface
• Many surface features due to the upwelling of heat.
• Particularly Sunspots and Prominences, as can be seen with a simple telescope and filter.
• Sunspots are magnetic storms that peak every 11 years, causing electromagnetic disturbances on the Earth.
• Streams of hot ionized gas that loop along the sunspot’s field lines are called prominances.
Details
• The hot gases of the Sun are electrically charged, so as it rotates magnetic fields are formed.
• Since the Sun isn’t solid like a planet, its equator rotates faster than its poles, stretching the magnetic field lines deep in the interior of the Sun.
• These get wrapped up, causing Sunspots.
In which century has sunspot activity been the greatest?
Perhaps a Global Connection?
And More Details…
• Sometimes the energy in a prominence is so great that it breaks free of the magnetic field and escapes into space, adding to the Solar Wind.
• The Solar Wind is a constant stream of charged particle blasting outward from the Sun.
• It is both a potential source of propulsion and dangerous radiation.
• The Sun’s atmosphere, called the Corona, is a superheated rarefied gas similar in composition to the Solar Wind.
Formation• The Sun condensed ~5 billion years ago out of an
enormous cloud of hydrogen, dust, and other gases called a Bok Globule.
• As the globule contracted due to gravity, angular momentum was conserved and the cloud spun faster and faster, becoming a protostar.
• Small bits of the protostar were cast out, like water in the spin cycle of a washer, to become the Solar System.
• Bands of this debris condensed, or accreted, into the planets, moons, and other denizens of nearby space.
• For 9 Gyr (billion years) the Sun is pretty much as it is now, though slowly increasing output
• At ~ 10Gyr the H in the core runs out and hydrostatic equilibrium fails
• The Sun expands out to beyond the orbit of Venus as a Red Giant
• Its He core contracts until it flashes into fusion at 100 million K.
• He burns in the core, H burns in a shell
• It will eject a large planetary nebula
• Left behind is its CNO core, known as a White Dwarf
The End of the Sun
• After 11 Gyr our Sun has ceased to do fusion
• About the size of the Earth, radiating due to gravitational heating
• Super dense!
• Will exist as a white dwarf for trillions of years, cooling off and becoming a black dwarf