1. CH29: The Sun
Mrs. Kummer, 2016

2. THE SUN
The Sun is the closest star to Earth and is the center of our solar system. A giant, spinning ball of very hot gas, the Sun is fueled by nuclear fusion reactions. The light from the Sun heats our world and makes life possible. The Sun is also an active star that displays sunspots, solar flares, erupting prominences, and coronal mass ejections. These phenomena impact our near-Earth space environment and determine our "space weather."
CHARACTERISTIC
STRUCTURE
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3. Characteristics of the Sun
Size: km in diameter
Mass: x 10³° kg
Density: kg/m³
Surface Temperature:5500 K
6000 K
THE SUN
STRUCTURE
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4. The Structure of Sun
THE SUN
CHARACTERISTIC
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5. Activities in the Sun
Sunspots
Solar Flares
Prominence

6. Fig. 3 Page 453

7. Sunspots
Sunspots appear as dark spots on the surface of the Sun. Temperatures in the dark centers of sunspots drop to about 3700 K (compared to 5700 K for the surrounding photosphere). They typically last for several days, although very large ones may live for several weeks.

8. Sunspot are areas where the magnetic field is about 2500 times stronger than the earth; much higher than anywhere else on the sun.

9. Spectrum analysis shows that sunspots have strong magnetic field, about 1000 times stronger than the Sun's average. Sunspots usually appear in pairs. The two sunspots of a pair have different polarities, one would be a magnetic north and the other is a magnetic south, and can be joined by magnetic field lines. The strong magnetic field locks the gas of the photosphere in places and inhibits the hotter gas below to rise at the sunspots. As a result, the sunspots are cooler. Sunspots appear to coincide with changes in the climate of the Earth. Studies show that during the last ice age, there were very few sunspots

10. Solar Flares
Solar flares are tremendous explosions on the surface of the Sun. In a matter of just a few minutes they heat material to many millions of degrees and release as much energy as a billion megatons of TNT. They occur near sunspots, usually along the dividing line (neutral line) between areas of oppositely directed magnetic fields.
Images from SOHO*
*NASA/ESA Solar and Heliospheric Observatory spacecraft

11. A solar flare is an eruption of hot gases from the inner atmosphere of the Sun’s surface. It travels very quickly and last for only minutes

12. The first solar flare recorded in astronomical literature was on September 1, Two scientists, Richard C. Carrington and Richard Hodgson, were independently observing sunspots at the time, when they viewed a large flare in white (visible) light.

13. Solar flares are thought to result from the build up and explosive release of magnetic energy in the solar atmosphere. The outer layer of the Sun is convective, meaning that the gas rolls up and down like in a pot of boiling water. This ionized gas (plasma) drags the Sun's magnetic field with it, twisting it and strengthening it. In some regions the magnetic field becomes particularly strong and breaks out into the solar atmosphere as discrete, loop-like structures.

14. In active regions where flares occur, these structures either interact or become internally unstable, giving a flare. The signs of a flare are gas rapidly heated to high temperatures, electrons and ions accelerated to high energies, and bulk mass motions.

15. The energy in the magnetic field is thought to be converted into these things through a process called magnetic reconnection, in which oppositely directed magnetic field lines "break" and connect to each other and part of their energy is transferred to the gas in the solar atmosphere.

16. Solar
Prominences
Prominences are dense clouds of material suspended above the surface of the Sun by loops of magnetic field. Prominences can remain in a quiet or quiescent state for days or weeks. However, as the magnetic loops that support them slowly change, prominences can erupt and rise off of the Sun over the course of a few minutes or hours

17. Unusually Large Solar Prominence as viewed by SOHO spacecraft in 1999
Solar Prominence as observed from the edge of the Sun
Unusually Large Solar Prominence as viewed by SOHO spacecraft in 1999 17

18. A solar prominence is a burst of a huge sheet of gases, also from the inner atmosphere. It is much larger than a flare and may last for days or even weeks.

19. A solar prominence (also known as a filament) is an arc of gas that erupts from the surface of the Sun. Prominences can loop hundreds of thousands of miles into space. Prominences are held above the Sun's surface by strong magnetic fields and can last for many months. At some time in their existence, most prominences will erupt, spewing enormous amounts of solar material into space.