Chapter One THE SUN Although the sun is a rather ordinary star it is very important to the inhabitants of Earth It is the source of virtually all Earth’s energy It provides the heat and light that make life on Earth possible Yet Earth receives only about half a billionth of the energy that leaves the sun The sun is a huge ball of hot gases Like other stars it produces enormous enormous amounts of energy by converting hydrogen to helium deep within its interior The sun looks like a burning sphere It is too hot however for an Earth-type chemical reaction such as burning to occur there Besides if burning produced its energy it would have run out of fuel long ago Instead thermonuclear reactions are the source of solar energy The vast amount of matter in the sun 8
THE SUN The sun is a yellow dwarf star a kind that is common in the Milky Way Galaxy Its diameter is about 864,950 miles 1,392,000 kilometers which is about 109 times the diameter of Earth can provide the fuel for billions of years of atomic reactions Astronomers believe that the sun is nearly halfway through its lifetime of 10 billion years STRUCTURE AND ENERGY PRODUCTION The sun can be divided into several different layers layers Energy is produced in the dense hot central 9
SOLAR POWER region which is called the core and travels outward outward through the rest of the interior interior The surface or the part of the sun that is visible from Earth in ordinary ordinary light is called the photosphere It emits most of the light and heat that reach Earth The surface is the innermost part of the solar atmosphere atmosphere The atmosphere atmosphere also has a thin middle layer called the chromosphere and a large outer layer the corona The corona gives rise to a flow of charged particles called the solar wind that stretches beyond Earth and the other planets The sun is too hot for matter to exist there as a solid or liquid Its matter consists of gas and plasma a state in which gases are so hot that the electrons are stripped away from their atomic nuclei The sun’s core is an extremely hot dense mass of atomic nuclei and electrons Its temperature is about 10
THE SUN 27,000,000 F 15,000,000 Kelvin and it is thought to be some 150 times as dense as water The pressure is enormous Normally protons in atomic nuclei repel each other because they have the same electrical charge Under the great density and pressure in the sun’s core however nuclei can collide and fuse into new and heavier nuclei This is a type of thermonuclear thermonuclear reaction called a fusion reaction The basic fusion process in the sun involves a series of reactions in which four hydrogen nuclei are ultimately converted into one helium nucleus The mass of the helium nucleus is about 0 7 percent less than that of the four hydrogen nuclei This 0 7 percent of the mass is changed into energy Every second the sun converts almost 700 million tons 635 million metric tons of hydrogen into about 695 million tons 630 million metric tons of helium Nearly 5 million tons 5 million metric tons of mass 0 7 percent of 700 million tons 630 million metric tons are converted to energy Some of this energy heats the plasma in the core and some escapes into space as nearly massless electrically neutral particles called neutrinos Some of the energy is in the form of gamma-ray photons These photons travel outward from the core through a zone in which the energy is carried mainly by 11
