Each kind of atom has a certain unique number of particles called protons, neutrons, and electrons in it. What they have learned about matter is that it is made up of different kinds of atoms В— hydrogen atoms, carbon atoms, and iron atoms, for example. Scientists have studied matter in their laboratories for many, many years. To understand why stars shine, we must first understand the tiny particles that make up matter. Planet Earth, our bodies, and shining stars are all made of the same basic elements of matter. Bethe won the 1967 Nobel Prize in Physics for his work concerning energy production in stars. The proton-proton cycle, as it is now called, is known to be responsible for about 98% of the SunВ’s energy production in its inner core. In 1938, Bethe and his colleagues presented a fully developed proton-proton chain of reactions that converts hydrogen into helium, which would allow the Sun to shine for about 10 billion years. Hans Bethe realized that a proton smashing into another proton with enough force could be the reaction to power the Sun. In 1920, British astronomer Arthur Eddington proposed that the Sun and other stars are powered by nuclear reactions. Where E is the energy released (in units called Joules) from the conversion of a mass m (in units of kg), and c is the speed of light (in meters per second). These quantities are related by the mass-energy relation In 1905, while developing his special theory of relativity, Einstein showed that mass can be converted into energy and vice-versa. However, this kind of contraction cannot be the main source of stellar energy for billions of yearsВ…a hundred million, maybe, but not a billion.ДЄ clue to the source of stellar energy was provided by Albert Einstein. This process does in fact happen in the protostar phase of stellar formation. Kelvin and Helmholtz argued that gravitational contraction would cause the Sun's gases to become hot enough to radiate heat energy into space. As it contracts, the gases in its interior become compressed and when a gas is compressed its temperature increases. In the mid-1800s two physicists, Lord Kelvin and Hermann von Helmholtz, put forward the idea that the huge weight of the Sun's outer layers should cause the Sun to gradually contract. However, calculations showed that a star powered on chemical energy would only last maybe a thousand years or so.

But just what generates this energy for such a long period of time? Scientists of the 19 th century believed that the Sun was powered by chemical reactions. Our Sun has provided an essentially constant amount of heat and light to Earth for about 4.5 billion years.

Every second, a star like our Sun converts 4 million tons of its material into heat and light through the process of nuclear fusion. The simple answer is that deep inside the core of the Sun, enough protons can collide into each other with enough speed that they stick together to form a helium nucleus and generate a tremendous amount of energy at the same time. What makes stars shine StarChild Question of the Month for September 1999 Question:

Nuke them till they glow