1. The Sun

4. Sun Facts Distance from Earth - 1 AU (1.5 x 108 Km)
Period of Rotation days at equator
Radius x 105 Km
Mass x 1030 Kg
Surface Temperature K
Spectral Type –G2

5. Sun Facts continued Apparent Visual magnitude – -26.74
Composition – 71% hydrogen, 27% helium, 2% heavier elements (C, Fe)
Age – 4.5 billion years

6. Structure of the Sun

7. Core : Radioactive Zone: Convection Zone:
gases 100 times denser than water
temperatures up to 15 million K
Radioactive Zone:
energy moves by radiation carried by photons
Takes photon 100,000 years to travel from core to surface
Convection Zone:
Lies below the Sun’s visible surface
Convention occurs because heated matter expands and becomes slightly less dense than cooler material around it.

8. Photosphere Sun’s visible surface.
Solar granulation are immense bubble of hot gas rising from deep within the sun.
Has a mottled structure.

9. Solar Atmosphere Chromosphere: Immediately above photosphere
Can be seen during solar eclipse
Contains millions of thin columns called spicules (short lived and last 5 to 15 minutes. They carry energy from lower regions).
Color comes from strong red emission lines in hydrogen.

10. Corona: Sun’s outer atmosphere Low density, extremely hot gas
Contains region of cooler gas called coronal holes.
Contains little energy

11. How Sun Works:
Hydrostatic Equilibrium requires the outward force created by pressure to exactly balance the inward force of the Sun’s gravity.
Because heat flows out of the hot core, Sun needs mechanism to replace core heat.
Sun generates its energy by nuclear fusion (a process that bonds two or more nuclei into single heavier one)

13. Sunspots Dark spots on photosphere.
Size: few hundred to a thousand Kilometers across.
They are cooler (4500 K) than the surface (6000 K)
They contain strong magnetic field.

14. Solar Magnetic Fields
Field is thousand times stronger than the earth which causes electrons to spiral in it.
Field slows ascent of hot gas in convection zone.
Galileo concluded Sun’s rotation carries sunspots around.

15. Sunspot Cycle 11 year cycle caused by differential rotation.
Equator rotates in about 25 days and its poles in 30 days.

16. The Sun’s rotation “wraps” the solar magnetic field into coils below the surface making the field stronger , increasing prominences and flares.

17. Sunspots occur in pairs: one with north polarity, one with south polarity. The polarity is opposite between hemispheres.

18. Full cycle of magnetic activity requires 22 years.

19. Other features
Solar flare is a sudden tremendous explosive outburst of light, invisible radiation.
They occur near sunspots.
Flares follow a coronal mass ejection (cme) which blasts plasma out from the corona.
CME may include prominences, fiery arches of ionized gases on the Sun’s limb.

21. Solar Wind is plasma or a stream of energetic,electrically charged particles that flow out of the Sun.
Solar Winds occur at CME. It is the strongest when solar activity is the greatest. Comes from coronal holes.
Coronal holes are regions in sun’s corona where gases are much less dense than elsewhere.

22. Powering the Sun
Sun generates energy by converting hydrogen into helium by a process called nuclear fusion.
This process requires such a high temperature that it can only occur in the sun.
H contains proton and election. He contains 2 proton, 2 neutrons and 2 electrons.