Lesson 7 notes

The Sun as an Energy Source

 

The Sun as a Star:

1.       The Sun is a major energy source for Earth.

2.       The Sun is an “average” star in size.

3.       In its present state it is approximately 4.5 billion years old – about the same age as Earth.

4.       In a few billion years the Sun will expand beyond the orbits of the inner planets, including Earth.

5.       The Sun then will cool and become a red giant star.

6.       After 100 million years or so it will become a small dense “white dwarf”.

Parts of the Sun

The sun is made of gas and has no solid surface as Earth does. However, it still has a defined structure. The three major surface areas of the sun are shown in the upper half of Figure 1:

·                     Core

·                     Radiative Zone

·                     Convective Zone


Photo courtesy SOHO consortium. SOHO is a project of international cooperation between the European Space Agency (ESA) and the U.S. National Aeronautics and Space Administration (NASA).
Figure 1. Basic overview of the parts of the sun. The flare, sunspots and the prominence are all clipped from actual SOHO

Above the surface of the sun is its atmosphere, which consists of three parts as shown in the lower half of Figure 1:

·                     Photosphere

·                     Chromosphere

·                     Corona - extremely hot outermost layer extending outward from the chromosphere several million miles or kilometers

We will see that all of the major features of the sun can be explained by the nuclear reactions that make its energy, the magnetic fields that are caused by the movements of the gas, and the immense gravity.

The Sun: A Nuclear Reactor:

1.       The Sun is a big ball of gas containing 78% hydrogen, 20% helium and 2 % heavier elements.

2.       The Sun has a strong gravitational pull.

3.       The hydrogen and helium in the Sun undergo a reaction, called nuclear fusion, by which hydrogen atoms are fused together to make one helium atom.

Temperature

Plasmas occur at very high temperatures - the electrons are stripped from the atomic nuclei.

Scientists call the change from hydrogen to helium a nuclear reaction.

 

4.       This reaction releases energy in the form of heat and light.

Solar Energy:

SOLAR ENERGY:

 

1.       Most of the heat energy in Earth’s atmosphere originates as energy from the Sun, or solar energy, which travels through space in the form of electromagnetic waves.

2.       The direct transfer of energy by electromagnetic waves is called radiation.

3.       Radiation transfers heat energy from one object to another without necessarily heating the space between the objects.

4.       Most of the Sun’s radiation does not reach Earth, about half is absorbed by land and water; the other half is reflected back into space or absorbed by the atmosphere.