World Builders™                                                                    Session One  --  Astronomy 

Earth and the Sun's Energy

The sun radiates an enormous amount of energy.

How much of it does our planet get? 

Only about one two billionth part of the energy that the sun sends out!

How is Energy Used on Our Planet?

     Well, first of all, 34% is just reflected back by clouds and ice. This energy goes out into space and is lost to us. The reflectivity of a planet or moon is called its albedo.

     42% of the energy goes to warm the land and water. When the earth turns and the warmed part is in darkness, some of this heat is radiated out into space.

     23% of the energy makes water evaporate. Without evaporation, there would be no rainfall, no redistribution of water.

     1% of the energy powers the wind and the ocean currents that affect our weather. These currents cause seasonal variations in rainfall, such as monsoons.

     0.023 of the energy is used for photosynthesis. Photosynthesis is the process by which plants take in carbon dioxide and water and, with the help of sunlight, turn it into glucose, water vapor and free oxygen. This process provides food and oxygen for all the animals. All life on earth is living on what the plants can do with .023% of the sun's energy!

     It is important to remember that the energy available to life is limited. Life forms struggle to get enough energy to keep on living and to reproduce. A small, stony island may support grass and small rabbits, but it will not support tigers and elephants because the grass cannot capture enough energy to support large animals. A few small predators, foxes, perhaps, will keep the rabbits from becoming so numerous that they eat all the grass. If the island is in a very cold climate the grass will grow more slowly, and perhaps the herbivores will be lemmings, which are smaller than rabbits. Some tiny islands support only plants, insects and a few visiting birds.