Saturday, July 31, 2010

Four Trillion Trillion Light Bulbs

Next time you are screwing in a light bulb, notice its wattage. A watt is a measure of power, or how much energy is produced or consumed each second. A 100 watt bulb uses 100 joules of energy every second. For comparison, the sun produces 4 1026 watts of power. That’s a lot of light bulbs—four trillion trillion of them, to be exact. This rate of energy production is called the sun’s luminosity. Many stars have luminosities much higher than that of the sun.
The source of the sun’s power—and that of all stars, during most of their lifetimes—is the fusing together of nuclei. Stars first convert hydrogen into helium, and heavier elements come later. The only fusion reactions that we have been able to produce on the earth are uncontrolled reactions known as hydrogen bombs. The destructive force of these explosions gives insight into the enormous energies released in the core of the sun. Nuclear fusion could be used as a nearly limitless supply of energy on the earth; however, we are not yet able to create the necessary conditions on Earth for controlled fusion reactions.

A Spectacular, Mediocre Star

In terms of its size, mass and energy released, the sun is by far the most spectacular body in the solar system. With a radius of 22.8 X108 feet (6.96 X108 m), it is 100 times larger than the earth. Imagine yourself standing in a room with a golf ball. If the golf ball is the earth, the sun would touch the eight-foot ceiling. With a mass of 1.99 1030 kg, the sun is 300,000 times more massive than the earth. And with a surface temperature of 5,780 K (compared to the earth’s average 290 K surface temperature), the sun would melt or vaporize any matter we know.

What’s Sun Made Of?

The sun is mostly hydrogen (about 73 percent of the total mass) and helium (25 percent). Other elements are found in much smaller amounts, adding up to just under two percent of the sun’s mass. These include carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron. Over 50 other elements are found in trace amounts. There is nothing unique about the presence of these particular elements; they are the same ones that are distributed throughout the solar system and the universe. In particular, hydrogen atoms of the sun’s core plow into one another to create helium atoms. In the process, a little mass is converted into energy. That little bit of energy for each collision means enormous amounts of energy when we count all of the collisions that occur in the core of the sun. The fact that c is a very large number means that a tiny amount of mass results in a very large amount of energy. With this energy source, the sun is expected to last not a thousand years, or even 100 million years, but about 8 to 10 billion years, typical for a star with the sun’s mass.