1. 24.3 – The Sun

2. Do Now
What are the four parts of the sun?

3. Do Now What are the four parts of the sun?
The solar interior, the photosphere, the chromosphere and the corona.

4. Key Words
Interior
Conversion

5. Vocab Words Photosphere Chromosphere Corona Solar Wind Sunspot
Prominence
Solar Flare
Aurora
Nuclear Fusion

6. The Sun
The sun is one of the 100 billion stars that make up the Milky Way galaxy.
It is the only star where we are able to study the surface and better understand what the surface of others stars may be like.
Compared to other stars, the sun is an “average star.” However, on the scale of our solar system, it is truly gigantic.
Its diameter is equal to 109 Earth diameters. Its volume is 1.25 million times as great as Earth’s. Its mass is 332,000 times the mass of Earth and its density is only ¼ that of solid Earth.

7. Structure of the Sun

8. Photosphere
Radiates most of the sunlight we see and can be thought of as the visible “surface” of the sun.
Consists of a layer of gas less than 500 kilometers thick; its neither smooth nor uniformly bright.
There is a grainy texture due to relatively small, bright markings called granules. They are about the size of Texas and they only last on the surface for about minutes before sinking back down due to cooling. Creating convection currents.
This is how energy is transferred on the sun.
Composition of the photosphere is 90% hydrogen and 10% helium.

9. Granules

10. Chromosphere
This lies just above the photosphere and it is a relatively thin layer of hot gases a few thousand kilometers thick.
This layer is observable only for a few minutes during a solar eclipse. It appears as a thin red rim around the sun.
Consists of hot, incandescent gases under low pressure, it produces an emission spectrum that is nearly the reverse of the absorption spectrum of the photosphere.

11. Chromosphere

12. Corona
The outermost portion of the solar atmosphere is very weak and, as with the chromosphere, is visible only when the brilliant photosphere is covered.
This envelope of ionized gases normally extends a million kilometers from the sun and produces a glow about half as bright as the full moon.

13. Corona

14. Solar Wind
At the outer fringe of the corona, the ionized gases have speeds great enough to escape the gravitational pull of the sun.
The streams of protons and electrons that boil from the corona constitute the solar wind.
Travel through the solar system at speeds up to 800 kilometers per second and eventually is lost into space.
Earth’s magnetic field prevents the solar winds from reaching our surface, but they do affect our atmosphere; creating an aurora.

15. Solar Wind

16. Sunspots
The dark regions on the surface of the photosphere, usually dark in the center.
Their temperature which is about 1500 K less than that of the surrounding solar surface.
They are still brighter than the full moon.
There is a cycle of observable sunspots varying every 11 years.
Maximum = A hundred or more visible
Minimum = Few or even none visible

17. Sunspots

18. Prominences
Among the more spectacular features of the active sun are prominences; which are huge cloudlike structures consisting of chromospheric gases.
Often appear as great arches that extend well into the corona.
Can reach speeds up to 1000 kilometers per second and may leave the sun entirely.
They are ionized gases trapped by magnetic fields that extend from regions of intense solar activity.

19. Prominences

20. Solar Flares
The most explosive events associated with sunspots are solar flares, which are brief outbursts that normally last about an hour and appear as a sudden brightening of the region above a sunspot cluster.
During their existence, solar flares release enormous amounts of energy, much of it in the form of ultraviolet, radio, and X-ray radiation. If the particles reach Earth, they can affect things like long-distance radio communications.

21. Solar Flares

22. Auroras
The most spectacular effects of solar flares on Earth are auroras; also called northern and southern lights.
Earth’s upper atmosphere near its magnetic poles is set aglow for several nights.

23. Nuclear Fusion
Deep in its interior, the sun produces energy by a process called nuclear fusion.
This nuclear reaction converts four hydrogen nuclei into the nucleus of a helium atom.
Tremendous energy is released.
During nuclear fusion, energy is released because some matter is actually converted to energy.
Our sun is thought to be middle-aged at 4.5 billion years old. 

24. Group Activity
On page 685, Figure 12, copy and label the diagram.