by L.S. Watts

Created on: February 25, 2012

The earth’s main energy source comes from the sun. It provides the earth with not only light but also warmth. Without the sun, Earth would be a cold and lifeless planet. But how exactly is the sun’s energy transferred to the earth?

Radiation

Radiation is the transfer of energy by visible light. Because the sun’s light is always shining on the earth’s surface somewhere, the sun is constantly warming the earth’s surface through a process called radiation. There are

three ways radiation is transferred to the earth’s surface. These include ultraviolet radiation, visible light, and other forms of electromagnetic waves.

About fifty percent of the solar radiation is absorbed by the earth’s surface both directly and indirectly. The rate of solar radiation absorption depends on the physical characteristics of the area. As an example, when water heats up, compared to land, the water cools down at a slower rate than on land.

The earth is always absorbing solar radiation but in turn it is also sending energy back into space. Only an estimated fifteen percent of the solar radiation is absorbed by the atmosphere. When it comes to reflecting the energy back toward space, only four percent is reflected from the earth’s surface, only six percent is reflected by the atmosphere, and around twenty percent is reflected from clouds.

Have you ever sat outside on a sultry, summer day and wondered why it is so hot outside? Most people assume it is because of the sun’s direct rays beating down through the atmosphere. However, much of the solar radiation that travels in short wavelengths thus not very well absorbed through the atmosphere. Instead, it passes through the earth’s atmosphere to be absorbed by the earth’s surface.

Keep in mind that the earth’s surface reflects a small percentage of this energy back toward the atmosphere. When this happens it is done so in longer wavelengths, which is then absorbed by the atmosphere instead of simply passing through. Thus, it warms the air by using the processes of conduction and convection.

Conduction

Conduction is when molecules collide and energy transfers. So how does this relate to how the sun heats the earth? Think about turning on the burner to your stove to heat a kettle of water. The hot burner represents the earth that has been heated by the sun’s rays and the water at the bottom represents the air in the lowest level of the atmosphere. The energy transfer

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