Properties of the sun

1. Introduction to Stars
A. The Sun
1. The star at the centre of our solar system.
2. The source of energy for all life on earth.

Earth

2. 3. Layers of the sun (Atmosphere)
a. Photosphere: Layer that emits the radiation we see.
b. Chromosphere: Layer of decreased density above the
photosphere.
c. Transition Zone: Layer of greatly increased temperature.
d. Corona: Outtermost, and thinnest layer.
e. As you move up, in general, temperature increases.
Photosphere
Chromosphere
Transition Zone
Corona

3. 4. Layers of the sun (Interior)
a. Convection Zone: Superheated gasses are in
continuous thermal convection.
b. Radiation Zone: Where energy is carried toward the
surface without the aid of convection.
c. Core: The site of high-energy nuclear reactions that
generate the suns enormous energy output.

4. 5. Solar Wind:
a. The Corona of the sun reaches temperatures in
excess of 1,000,000K.
b. The molecules in this layer of the sun therefore
have enough energy to escape from the suns
gravity.
c. These particles have VERY high energy and form
what is called the solar wind.
d. The earth is protected from these particles by the
Earth’s magnetic field.

5. 6. The sun in X-Rays:
a. Recall that as the temperature of a substance
increases, the frequency of the light it emits
increases.
b. With temperatures well in excess of 1,000,000K the
corona of the sun emits in the X-Ray band.
c. Thus one of the best tools for studying the sun has
been X-Ray telescopes in Earth’s orbit.

7. 7. Luminosity: The measure of the energy put out by
the sun.
a. Imagine a detector 1m
2
that measures the
sunlight that hits it.
b. You would find that the energy that hits the
detector every second is roughly equal to:
1400 watts
This is known as the Solar Constant

8. 7. Luminosity continued:
c. This is NOT the measure of the total output by the
sun because it radiates in all directions.
d. The energy collected by our detector is only a
VERY small portion of the total output.

9. 7. Luminosity continued:
e. Imagine a sphere surrounding the sun with a radius
of 1au.
f. The Total energy output of the sun is equal to the
amount of energy hitting our imaginary sphere.

10. 6. Luminosity continued:
g. Our detector 1m
2
detector is just one small part of
the total surface area of the sphere.
h. Calculating the surface area of a sphere… 4(pi)r
2
i. If each 1m
2
gets 1400w what is the TOTAL energy?
j. This value is called the luminosity of the sun.

11. 7. Luminosity continued:
g. Our detector 1m
2
detector is just one small part of
the total surface area of the sphere.
h. Calculating the surface area of a sphere… 4(pi)r
2
i. If each 1m
2
gets 1400w what is the TOTAL energy?
j. This value is called the luminosity of the sun.

12. Introduction to Stars
A. The Sun
8. Solar Magnetism & Sunspots
a. Sunspots are dark areas in the photosphere
of the sun.
b. Average 1000K cooler then the surrounding
photosphere and 1000x stronger magnetic
field.

14. 8. Solar Magnetism & Sunspots
c. Because of the Sun’s rotation, the field lines do not run
directly north and south as the Earth’s.

16. d. The rotation drags the
lines and creates “kinks”,
which is where sunspots
form.
e. Sunspots normally
come in pairs of opposite
magnetic charge.

17. 9. The Solar Cycle
a. The sun goes through 11 year cycles of high and low
sunspot activity.
b. We are currently at the low point of the cycle.

19. 9. The Solar Cycle
c. The number of sunspots is linked to the amount of
material ejected from the sun.
d. Prominences are large sheets of material ejected
from the sun in loops.

20. 9. The Solar Cycle
e. Solar Flairs are
ejected material
like a prominence
but in in a matter
of seconds or
Minutes.