1. The Sun’s Layers and Solar Activity

2. The Sun’s Layers
Like other stars, the Sun is an enormous ball of gas that produces energy by fusing hydrogen into helium in its core.

3. The Sun’s Layers
This energy travels outward through the radiation zone and the convection zone.

4. The Sun’s Layers
In the convection zone, gases circulate in giant swirls.
Finally, energy passes into the Sun's atmosphere.

5. The Sun’s Atmosphere
The lowest layer of the Sun's atmosphere and the layer from which light is given off is the photosphere.
The photosphere often is called the surface of the Sun.
Temperatures there are about 6,000 k.

6. The Sun’s Atmosphere Above the photosphere is the chromosphere.
This layer extends upward about 2,000 km above the photosphere.

7. The Sun’s Atmosphere
A transition zone occurs between 2,000 km and 10,000 km above the photosphere.

8. The Sun’s Atmosphere Above the transition zone is the corona.
This is the largest layer of the Sun's atmosphere and extends million of kilometers into space.

9. The Sun’s Atmosphere
Temperatures in the corona are as high as 2 million K.
Charged particles continually escape from the corona and move through space as solar wind.

10. Surface Features
From the viewpoint that you observe the Sun, its surface appears to be a smooth layer.
But the Sun's surface has many features, including sunspots, prominences, flares, and CMEs.

11. Sunspots
Areas of the Sun's surface that appear dark because they are cooler than surrounding areas are called
sunspots.
Because scientists could observe the movement of individual sunspots, they concluded that the Sun rotates.

12. Sunspots
The number of sunspots increases and decreases in a fairly regular pattern called the sunspot, or solar activity, cycle.
Times when many large sunspots occur are called sunspot maximums.
Sunspot maximums occur about every 10 to 11 years.

13. Prominences and Flares
The intense magnetic fields associated with sunspots might cause prominences, which are huge, arching
columns of gas.
Some prominences blast material from the Sun into space at speeds ranging from 600 km/s to more than 1,000 km/s.

14. Prominences and Flares
Gases near a sunspot sometimes brighten suddenly, shooting outward at high speed.
These violent eruptions are called solar flares.

15. CMEs
Coronal mass ejections (CMEs) occur when large amounts of electrically-charged gas are ejected suddenly from the Sun's corona.
Images from the Sun

16. How the Sun Affects the Earth
The large amount of charged gas from a CME can damage satellites in orbit around Earth.
It also can interfere with radio and power distribution equipment.

17. How the Sun Affects the Earth
CMEs often cause auroras.
High energy particles contained in CMEs and the solar wind are carried past Earth's magnetic field.
This generates electric currents that flow toward Earth's poles.

18. How the Sun Affects the Earth
These electric currents ionize gases in Earth's atmosphere.
When these ions recombine with electrons, they produce the light of an aurora.
Space Weather

19. Why Do We Have Seasons?
The interaction between the Sun and the Earth also causes our seasons.
The Earth is tilted 23.5° on its axis.

20. Why Do We Have Seasons?
This means that the Northern Hemisphere is tilted toward the sun during the summer months.
The sunlight reaches us more directly, causing the warmer temperatures.

21. Why Do We Have Seasons?
The opposite is true during the winter – the Northern hemisphere tilts away from the sun, receiving less-direct sunlight causing colder temperatures.
Spring and Fall are the transitions.

22. Why Do We Have Seasons?
This is also why the Southern hemisphere has seasons opposite of us!
Earth’s Tilt and the Seasons

23. REVIEW

24. Question 1
The layer of the Sun’s atmosphere from which light is given off is the _________.
A. chromosphere
B. corona
C. photosphere
D. prominence

25. Answer
The answer is C.
The photosphere is also called the surface of the Sun.

26. Question 2
Areas of the Sun’s surface that appear dark because they are cooler than surrounding areas are called __________.
A. coronas
B. prominences
C. spectral waves
D. sunspots

27. Answer
The answer is D.
Sunspots are not permanent features on the Sun.

28. Question 3 Which layer of the Sun’s atmosphere is the largest?
A. chromosphere
B. convection zone
C. corona
D. photosphere

29. Answer
The answer is C.
The corona lies above the photosphere and extends millions of kilometers into space.