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

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

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.

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.

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. Luminosity: The measure of the energy put out by the sun.

a. Imagine a detector 1m2 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

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.

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.

6. Luminosity continued:

g. Our detector 1m2 detector is just one small part of the total surface area of the sphere.

h. Calculating the surface area of a sphere… 4(pi)r2

i. If each 1m2 gets 1400w what is the TOTAL energy?

j. This value is called the luminosity of the sun.

7. Luminosity continued:

g. Our detector 1m2 detector is just one small part of the total surface area of the sphere.

h. Calculating the surface area of a sphere… 4(pi)r2

i. If each 1m2 gets 1400w what is the TOTAL energy?

j. This value is called the luminosity of the sun.

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.

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.

d. The rotation drags the lines and creates “kinks”, which is where sunspots form.

e. Sunspots normally come in pairs of opposite magnetic charge.

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.

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.

9. The Solar Cycle

e. Solar Flairs are

ejected material

like a prominence

but in in a matter

of seconds or

Minutes.