Exploring the Layers of the Sun

1. The Sun, Our Star

2. Mid-size, middle-aged star • 300,000 times the Earth’s mass • 100 times bigger in diameter than Earth • made mostly of plasma: ionized gas particles and the most abundant form of matter in the solar system (not solids, liquids, or gases) • Burns 600 million tons of hydrogen in its core every second! • Releases the energy of 100 billion nuclear bombs in that time! • surface temperature = 5,780 K (9,900 °F) • Core temperature = 15 million K (~ 27 million °F) • Composed of 71% H, 27% He, 2% heavier elements

3. The Layers of the Sun Copy this.

4. I. Photosphere • visible surface of the Sun • helps Sun retain heat by reducing the amount of fuel (H) it consumes • 6,000 K

5. II. Radiative Zone • energy carried by photons* move through this region from the core • gas is so dense here, it takes 16 million years for photons to move through it! *Photons are little bundles of light energy that behave like a particle and a wave at the same time.

6. III. Convection Zone • just below the photosphere • gas is cooler here • convection currents carry energy to the surface • the convective motion can be inferred by the numerous tiny, bright regions surrounded by narrow darker zones called granulation Bright patch Dark area Solar granulation near a sun spot. The bright patches are immense bubbles of hot gas rising from deep within the Sun. The darker areas are cooler gas sinking back into the Sun’s interior.

7. IV. Core • where nuclear fusion takes place • - process where hydrogen is converted into helium by bonding two H nuclei into a single, heavier He nucleus • creates the outward pressure that helps maintain the Sun’s structural integrity: hydrostatic equilibrium • The Sun’s inward force arises from its own gravity. • The outward force arises from the rapid motion of atoms, a motion that gives rise to a pressure.

8. Diagram of the proton-proton chain. The Sun’s power comes from the conversion of its mass to energy by nuclear fusion.

9. Neutrinos, sub-atomic particles created in the Sun’s core when H fuses to form He, have no electric charge and only a tiny mass. This gives them phenomenal penetrating power. • They escape from the core and into space like bullets through wet Kleenex. They then pass straight through the Earth and anything on it, like you, and keep going. • Roughly a trillion neutrinos from the Sun pass harmlessly through your body every second.

10. How do they know this, you ask? Water molecules will give off a flash of light when struck by a neutrino. Neutrino detectors use hundreds of thousands of liters of of these materials in a container buried under many tens of meters of rock to shield the detectors from other energetic particles from space called cosmic rays. Even the largest detectors detect only a few dozen neutrinos in a year.

11. Cosmic rays are all the protons, electrons, and other subatomic particles that constantly shower our planet. They travel at nearly the speed of light and are thought to be particles blasted from across space when a massive star explodes. Cosmic rays can penetrate only a short distance into the Earth, so that’s why neutrino detectors are buried deep inside to filter out the other particles. Neutrinos are so small, they could travel through a light year of lead and still only have a 50/50 chance of hitting an atom!

12. V. Chromosphere • lies immediately above the photosphere • the Sun’s lower atmosphere • Can be seen in a total eclipse of the Sun • contains millions of thin columns called spicules, each a jet of hot gas thousands of kilometers long. Moon blocking the sun in an eclipse

13. VI. Corona • where the chromosphere ends and the temperature shoots up to about 1 million degrees F • Sun’s outer atmosphere • extremely hot gas, low density gas • can only be seen in a total solar eclipse Moon blocking the Sun

14. Solar Magnetic Activity • Sunspots are the most common type • large, dark-appearing regions on the Sun’s surface • range from a few hundred to many thousand km across • darker because the surrounding gas is cooler • cooler because they contain strong magnetic fields

15. Same picture as classroom poster

16. Want to see today’s sunspot activity? This was Tuesday’s picture. Solar Wind- speed: 637.2 km/s - density: 2.6 protons/cm3 http://www.spaceweather.com/

17. Prominences and Solar Flares • 1. Prominence • magnetic disturbances in the low-density, virtually transparent, hot gases above the Sun’s visible surface. • huge plumes of glowing gas that juts from the lower chromosphere into the corona A Twisted Solar Eruptive Prominence • Prominences form where the Sun’s magnetic field reduces heat flow to a region. They are cooler than the gas around them, which means the pressure inside is less than outside.

18. 2. Solar Flares • sunspots give birth to these • brief but bright eruptions of hot gas in the chromosphere • violent, but localized • can increase the Sun’s radio and X-ray emission by factors of a thousand in a few seconds

19. Solar flares help to create the aurora borealis, or the northern lights.

20. Solar flares can also be strong enough to disrupt communications here on Earth by interfering with radio and satellite transmissions and frying electronic circuitry in space craft.