Lynda Cofer, age 14, of Clarkston, Washington, for her question:
How much energy do we get from the sun?
Suppose the sun produced peas all year and shot them out in all directions at a steady rate of one billion per second. Just two of the little round missiles from the celestial pea shooter would strike the earth every second. During a year, every spot on land and sea would get a quota of whacks.
Our beaming sun, of course, is a nuclear powerhouse pouring forth electromagnetic energy from every spot on its surface. In units of horse power, its total output has been estimated to be around 50 followed by 23 zeros. One part in 200 million strikes the planets. The rest fans on out across the universe as light that winks at other stars, and as radio, X rays and other wave lengths of electromagnetic energy. One part in half a billion parts of this fabulous energy is intercepted by our orbiting earth. It speeds across 93 million miles of interplanetary space at 186,000 miles a second. The light beam that dust struck your face left the surface of the sun about 8 1/2 minutes ago.
The average amount of solar energy that reaches the earth is estimated to be around 170 million billion watts. This equals about 126 million million horsepower. If all thin solar radiation reached the ground in usable forms, it would supply more than 50,000 horse power units of energy for every human person. But only about 75 million billion watts, less than half the total quota, reaches the surface of the land and seas.
About 55 per cent of our share of solar energy is reflected back into space or absorbed by our blanketing atmosphere. We sometimes see a fraction of our reflected sunlight as earthshine on the face of the New Moon. The rest bounces off into space and is wasted. The atmosphere stops a minimum of 15 per cent of our quota of solar energy from reaching the surface. The clouds that shroud about half the globe screen out up to 40 per cent.
The atmosphere tends to filter out ultraviolet ray, Xrays and the penetrating particles of solar energy that are dangerous to living tissues. Our thick, airy blanket is a shield that protects both plant and animal life from exposure to these types of radiation.
Our total quota of solar energy, or course, does not strike the surface of the globe evenly. It falls upon only one side of the rotating earth at a time. It falls in larger quantities from straight rays when the sun is directly overhead. Slanting sunbeams pierce through thicker slices of atmosphere _ and lose up to 90 per cent of eht heat before they reach the surface.
On every spot of the earth's surface, the solar energy varies with the day and the seasons, with weather conditions and with the sloping surface of the globe. At the top of the atmosphere, an area 10 by 12 inches square gets enough solar energy to run a 60 watt lamp and more than half of this is lost on the way down.
Scientists have estimated how the earth budgets its quota of energy from the sun. About 25 per cent of the total is used to evaporate 1,000 billion tons of moisture. Another 2 1/2 per cent powers the winds and ocean currents. The earth's plant life absorbs roughly, 8 per cent of our global solar energy. This portion indirectly supplies our oxygen, our vegetables and food for the animals that give us meat and dairy products. Plants store the sunshine of ages. Our coal, petroleum and other fuels are drawn from their reservoirs of ancient solar energy.