1. The Sun, our favorite star!
The Sun is the basis for all of our knowledge of stars. Why?
WE CAN SEE IT REALLY WELL.

2. Kelvin Temperature Scale
degree Celsius
degree Fahrenheit
symbol K °C °F
boiling point of water
373.15
100.
212.
melting point of ice
273.15 0.
32.
absolute zero
Humans
310 37
98.6
Sun
5800
5527
9980

3. Today we will take a journey from the center of the Sun, starting just outside the core…
…and ending up deep in the corona.

4. Overview of Solar Structure (aka, our Sun as a jawbreaker)
The Sun is made of mostly HYDROGEN and HELIUM
Main Parts:
Corona
Chromosphere
Photosphere
Convection Zone
Radiative Zone
Core

5. Rotation
25 Days at the Equator
35 Days at the Poles

6. This twisting leads to the loopy structures we see!

7. The Core + Energy Fusion takes place here. p n 4H 1He Fusion Animation

8. The interior of the Sun…
Energy is generated in the core, but how does it get out and end up as sunshine?
The next two layers of the Sun are all about getting the energy being made in the core out into space!

9. How does energy get from one place to another?
1. Convection
2. Conduction
3. Radiative Diffusion
Convection and Radiative Diffusion are most important for the Sun!

10. Radiative Diffusion
The photons “diffuse” outwards, heating the gas as they go.
Ionized gas
Photons can “scatter” off of unbound electrons
When they scatter, the photons share their energy with the electrons
The electrons get hotter

11. The Radiative Zone Ionized gas
Here, photons bounce around in a “random walk”
Eventually they make it out of the radiative zone, but it takes a long, long time!
Ionized gas

12. Convection Hot stuff rises… Cool stuff sinks!
Hot water goes up to the surface while cool water sinks down -- cool water then gets heated and rises
a.k.a: BOILING

13. As seen from the top, these are the granules we see in the photosphere
The Convective Zone
Photosphere
The Convective Zone is the layer just under the photosphere
Convective “cells”:
As seen from the top, these are the granules we see in the photosphere

14. Not very important for stars!
Conduction
Metal of the pan heats by conduction…
…heat travels through the atoms of the pan
Not very important for stars!

15. PHOTOSPHERE Characteristics the part of the sun we see
one of the coolest parts at 6000K
densest part of solar atmosphere
contains sun spots, granules (ation)

16. Photosphere temperature is about 5800 K…
Remember how the temperature and color of stars are related? The temperature of our Sun gives it its yellowish color!
Our Sun is really yellowish green, but our atmosphere absorbs and scatters some of the blue light.

17. The photosphere has some interesting features too…
Sunspots:
Regions where magnetic field pokes through the photosphere.
Sunspots are cooler than surrounding stuff, so they look dark!
Granules:
Where the roiling, boiling convection zone underneath bubbles up.

18. Sunspots dark cooler (4000K vs. 5800K) regions on the sun
last several days to several weeks
caused by the sun’s magnetic field upwelling to the
photosphere
occur in cycles
contribute to solar storms such as flares and coronal
mass ejections

19. in this image to someone in class
Sunspot pairs
Describe what you see
in this image to someone
in class

20. Explain what you see in this picture to
someone else in class.

21. Granulation Cover the sun’s surface approx. 1000km across
(Texas sized)
tops of convection cells
white centers are hotter
than dark edges
flow can be up to
15000 mph
individual cells last
20 min

23. CHROMOSPHERE Characteristics red color due to hydrogen emission lines
temperature 4500K to 10000K
prominences form here
2500 km thick
spicules (jets of plasma) form here

24. Spicules small jet like eruptions that last a few minutes
send material out into corona at km/s

25. TRANSITION REGION Region of rapid temperature change between
chromosphere and corona

26. THE CORONA temperature 1-3 million K very irregularly shaped
strong x-ray emitter
uncertain as to why it is so hot
coronal holes are the origin of the
solar wind
produces an absorption and
continuous spectrum

27. Coronal Mass Ejections
Huge bubbles of gas ejected
from the sun
Can cause problems with
communications
Often occur with flares

28. SOLAR WIND low density gases (ionized hydrogen)
travels 300 to 1000km/s
sun loses 10,000,000 tons of mass per year
Current Solar Wind
Data can be found at

29. A short Video
Earth to scale.
Yes, really.