1. The Sun

2. 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%).

3. 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.

4. 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.

5. 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.

6. 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

7. Heat Flow The core of the Sun is about 15 million degrees. Using E = mc 2, 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.

8. 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.

9. 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.

11. 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.

12. In which century has sunspot activity been the greatest?

13. Perhaps a Global Connection?

14. 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.

15. 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.

16. 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

17. 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