Lesson 3.3:

1. Lesson 3.3: The Sun

2. Lesson 3: • What is the structure of the sun? • What features can you see on the sun?

3. What Is the Structure of the Sun? • No solid surface • ¾ of sun’s mass is hydrogen • ¼ of sun’s mass is helium • Has an interior and an atmosphere • Interior is made up of the: • Core • Radiation zone • Convection zone

4. The Sun’s Interior: The Core • Core: central region of the sun • An enormous amount of energy is produced here through nuclear fusion • Nuclear fusion: when hydrogen atoms join to form helium

5. The Sun’s Interior: The Radiation Zone • Energy produced in the sun’s core moves outward through the radiation zone • Radiation zone: a region of very tightly packed gas where energy moves mainly in the form of electromagnetic radiation • Is extremely dense; energy can take more than 100,000 years to move through this zone

6. The Sun’s Interior: The Convection Zone • Convection zone: the outermost layer of the sun’s interior • Hot gases rise from the bottom of the convection zone and cool as they approach the top • Cooler gases sink, forming loops of gas that move energy toward the sun’s surface (convection currents)

7. The Sun’s Atmosphere • Stretches far into space • Layers become less dense the farther they are from the radiation zone • Mostly composed of hydrogen and helium • Includes the: • Photosphere • Chromosphere • Corona

8. The Sun’s Atmosphere: The Photosphere • Photosphere: the inner layer of the sun’s atmosphere • Considered to be the surface layer of the sun • Sun does not have a solid surface, although the gases of the photosphere are thick enough to be visible • When you look at an image of the sun, you see the photosphere

9. The Sun’s Atmosphere: The Chromosphere • Chromosphere: the middle layer of the sun’s atmosphere; means “color sphere” • The reddish glow visible around the photosphere at the start and end of a total eclipse

10. The Sun’s Atmosphere: The Corona • Corona: the outer layer that looks like a white halo around the sun; means “crown” • Extends into space for millions of kilometers • Gradually thins into streams of electrically charged particles called the solar wind

11. What Features Can You See on the Sun? • Using special telescopes to study the sun, scientists have spotted features like: • Sunspots • Prominences • Solar flares

12. Sunspots • Sunspots: dark areas on the sun’s surface; caused by areas of gas on the sun’s surface that are cooler than the gases around them • Often look small, but they can be larger than Earth • Number of sunspots varies in a regular cycle, with the most sunspots appearing about once every 11 years Sunspots

13. Prominences • Prominences: huge loops of gas; often link different parts of sunspot regions Prominences

14. Solar Flares • Solar flares: eruptions that occur when the loops in sunspot regions suddenly connect, releasing large amounts of magnetic energy • The energy heats gas on the sun to millions of degrees Celsius, causing the gas to erupt into solar flares

15. Solar Wind • Made up of electrical particles from the sun • Solar flares can increase the solar wind, meaning that more particles reach earth’s upper atmosphere • Earth’s atmosphere usually blocks these particles, except near the North and South poles • There, they create powerful electric currents that cause gas molecules in the atmosphere to glow, creating the auroras • They can also cause magnetic storms