This process, called gravitational contraction, could release a great deal of energy. One 19th-century theory said that this gravitational attraction causes the Sun to shrink and its matter to become more tightly packed. All the bits of matter in the Sun exert gravitational attraction on each other. Various theories have been advanced to explain the Sun’s tremendous energy output. Besides, if burning produced its energy, it would have run out of fuel very long ago. It is too hot, however, for an Earth-type chemical reaction such as burning to occur there. The corona gives rise to a flow of charged particles called the solar wind that stretches beyond Earth and the other planets. The atmosphere also has a thin middle layer, called the chromosphere, and a large outer layer, the corona. The surface is the innermost part of the solar atmosphere. It emits most of the light and heat that reach Earth. The surface, or the part of the Sun that is visible from Earth in ordinary light, is called the photosphere. Energy is produced in the dense, hot central region, which is called the core, and travels outward through the rest of the interior. The Sun can be divided into several different layers. The parts of the surface near the poles take 36 days to complete a rotation. The parts of the surface near the equator spin the fastest, completing one rotation about every 25 Earth days. Because the Sun is not solid, different parts of it rotate at different rates.
Gas of sun corona free#
The free electrons carry a negative charge, and the atomic nuclei carry a positive charge. The heated gas is said to be ionized because it consists of a group of ions, or electrically charged particles. Rather, the Sun’s matter consists of gas and plasma, a state in which gases are heated so much that the electrons are stripped away from their atomic nuclei. It is much too hot for matter to exist there as a solid or liquid. By mass, the Sun is about 71 percent hydrogen and 28 percent helium. Most of the rest are helium, with much smaller amounts of heavier elements such as carbon, nitrogen, oxygen, magnesium, silicon, and iron. More than 90 percent of the Sun’s atoms are hydrogen. Its volume is about 1,300,000 times Earth’s volume, and its mass, or quantity of matter, is some 333,000 times as great as Earth’s mass. Its diameter is about 864,950 miles (1,392,000 kilometers), which is about 109 times the diameter of Earth. It has a surface temperature of about 5,800 K (10,000 ☏). (The Kelvin temperature scale uses degrees of the same size as Celsius, or centigrade, degrees, but it is numbered from absolute zero, −273.15 ☌.) The Sun is a yellow dwarf star, a kind that is common in the Milky Way Galaxy. In color they range from whitish blue stars with very high surface temperatures (more than 30,000 Kelvin, or 53,500 ☏) to relatively cool red stars (less than 3,500 K, or 5,840 ☏). They range from giant stars, which are much larger than the Sun, to dwarf stars, which can be much smaller than the Sun. It is the only star whose surface details can be observed from Earth. Because the Sun is so close to Earth, it seems much larger and brighter than other stars. Light from the center of the galaxy takes many thousands of years to reach Earth. The Sun is in the outer part of the Milky Way galaxy. However, light from the next nearest star, Proxima Centauri, takes more than four years to arrive. Light from those other suns, the stars, takes much longer to reach the Earth. Light travels through space at about 186,282 miles (299,792 kilometers) per second, so a ray of sunlight takes only about 8 minutes to reach Earth. The average distance between the Sun and Earth is roughly 93 million miles (150 million kilometers). The immense pull of its gravity holds the planets, dwarf planets, asteroids, comets, and other bodies in orbit around it. It contains more than 99 percent of the system’s mass. The Sun lies at the center of the solar system.
( See also amateur astronomy, “Using Telescopes.”) Position in the Solar System One safe way to observe the Sun is to project its image through a pinhole or telescope onto a white screen or white cardboard.
Dark glasses and smoked glass provide no protection. Radiation from the Sun’s rays can damage one’s eyes, so one should never look directly at the Sun with unaided eyes or with a telescope (unless it is equipped with a special solar filter). Like other stars, it produces enormous amounts of energy by converting hydrogen to helium deep within its interior.īecause this energy is so intense, there are some real dangers in staring at the Sun. Yet Earth receives only about half a billionth of the energy that leaves the Sun. It provides the heat and light that make life on Earth possible. The Sun is the source of virtually all Earth’s energy. Although the Sun is a rather ordinary star, it is very important to the inhabitants of Earth.
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