1. The Centre of the Solar System Earth Science 11
Visible light view of sun
Ultraviolet image of the sun
The Sun
Radio wave view of sun
The Centre of the Solar System
Earth Science 11
Infrared image of the sun
X-ray image of sun

2. Like our Earth, the sun is made up of different layers.

3. Sun’s Atmosphere
Photosphere – a thin "sphere of light", the visible surface of the Sun (5 800 K)
Below the photosphere the sun is too dense for light to escape. Above the photosphere the sun is not dense enough to emit detectable light.
In actual fact, the photosphere is less dense than the air we breath! (3400 times less dense!)

4. Photosphere

5. Sun’s Atmosphere
Chromosphere – “sphere of colour” visible during solar eclipse; it is the inner atmosphere of the sun (10 000K)
It is 1000 times fainter than the photosphere.
It is 108 times less dense than the air we breathe.

6. Chromosphere

7. Sun’s Atmosphere
Corona – is the sun’s outermost atmosphere. The outflow of gas in this region is called the solar wind. The solar wind is made of protons and electrons that have escaped the sun’s gravity.
It has a temperature of K.
It has a density as low as 1 to 10 atoms / cm3

9. Corona

11. 1 = photosphere, 2 = chromosphere, 3 = corona
Why the outer layers of the Sun’s atmosphere are hotter is a puzzle.
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12. Basic Structure of the Sun
Average Density = 1.4 g/cm3
94.3% Hydrogen
5.6% Helium
0.1% Metals
Surface Temperature = 5762 K
Core Temperature = 15,000,000 K

13. By radiation and convection
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14. The Sun's Interior
Thermonuclear core - the central region of Sun where fusion takes place due to high temperatures and pressures.
Convection zone - a layer inside a star where energy is transported outward by means of heat flow through the gases of the star (convection).

15. From the surface of the sun moving inward, density increases and temperature increases.

16. Surface Features
Granules – are convection (heat) features about 1000 km in diameter and are seen constantly in the solar photosphere. They last for only 10 to 20 minutes before fading away.
Sunspots - are temporary cool regions in the solar photosphere created by magnetic fields.
They occur over an 11 year cycle.

17. Granules on the Sun’s surface
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A prominence

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19. Note the darker inner umbra and the outer penumbra
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20. Sunspots can be used to measure the rotation of the Sun
Near the equator the Sun rotates once in 25 days.
The poles rotate more slowly, about once every days.

21. Sunspots are low temperature regions in the photosphere
Sun spots are about 4000 K (2000 K cooler than solar surface) and have magnetic fields up 1000 the normal solar magnetic field. They can be as large as 50,000 km and last for many months.
The large magnetic fields in sunspots decrease the flow of heat via convection causing the sunspot to become cool.

22. Sunspot cycle
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23. The Magnetic Dynamo
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26. Solar Magnetic Fields Also Create Other Surface Phenomena.
Prominences
Flares
Solar wind
Coronal mass ejections

27. Prominences: Cooler Than Photosphere.
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28. Solar flares - Hotter, up to 40,000,000 K More energetic
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29. Coronal mass ejections - eruption of gas, can reach Earth and affect aurora, satellites
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30. Coronal Mass Ejection
Earth’s magnetic field shields us from most of the damaging solar winds.
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31. Solar Prominences:
Are large sheets of dense, cooler glowing gases which burst out of the chromosphere.
Can last for days or weeks.
Are as large as km or more!
Most of them eject material into the solar wind.

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33. A solar prominence compared to the Earth!
Photo taken by NASA space probe SOHO
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34. Large Eruptive Prominence
24 July 1999
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35. Solar Flares
Bursts of energy that travel outward from the chromosphere.
They last only a few minutes.

36. Solar Flares
Happen when magnetic field in an active region suddenly changes its structure.
Large numbers of rapidly-moving ions and electrons are released.
Much more energetic eruption than a prominence.
These energetic particles collide with coronal gas and raise its temperature up to 40 million K.

37. Solar Flares They contribute up to 1% to the Sun’s brightness.
Most of this is X-ray and UV radiation that reaches Earth in about 8 minutes.
Electrons and ions reach Earth in a few hours or days.

38. Effects of a Solar Flare on Earth
Ionization of Earth’s upper atmosphere is increased.
Enhancement of ionosphere disrupts long-range radio communications.
Power surges may occur, causing damage to transformers and blackouts.

39. Effects of a Solar Flare on Earth
Eventually, ejected coronal matter also reaches Earth.
Unless they are shielded for protection, astronauts are at risk from increased radiation.
The northern and southern lights are brighter than usual and are seen farther away from the poles.

40. Coronal Holes
Coronal holes are low-density regions associated with the sun’s magnetic field. Solar winds escape from coronal holes.
False colour uv image of coronal hole (dark).

41. Coronal Mass Ejections
Increase in number as sunspot number increases
Can eject billions of tons of matter at speeds of up to 1000 km / s!

42. Our Sun in Different Wavelengths
X-Ray
Ultraviolet
Visible
Infrared
Radio
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43. By observing the Sun in different parts of the spectrum, we can get information about the different layers in the Sun's atmosphere.
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X-ray images show us the structure of the hot corona, the outermost layer of the Sun. The brightest regions in the X-ray image are violent, high-temperature solar flares.

44. The ultraviolet image show additional regions of activity deeper in the Sun's atmosphere.
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45. In visible light we see sunspots on the Sun's surface.
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In visible light we see sunspots on the Sun's surface.

46. The infrared photo shows large, dark regions of cooler, denser gas where the infrared light is absorbed.
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47. The radio image show us the middle layer of the Sun's atmosphere.
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48. What makes the Sun shine?
Thermonuclear fusion at the Sun's core is the source of the Sun's energy.
Fusion is the joining of lighter nuclei to form a heavier, different element. As a result, energy is released.
This energy is radiated outward toward the convection zone.
Only at the core is the temperature and density high enough for fusion to occur.

49. What Makes the Sun Shine?

50. What makes the Sun shine?
1 Helium Atom + Energy
fusion
4 Hydrogen Atoms
E = mc2