The Sun is the center of the solar system. It was created when an immense disk of swirling gas and dust began condensing on itself. This condensing eventually formed the sun and the left over debris formed the other objects in the solar system. All of these objects are victims of the sun's gravity. They are all in their permanent positions orbiting the sun.
The Sun is a star of average size and strength. It is a class yellow star. The sun appears much larger to us because of its closeness compared to other stars. The sun is only 93 million miles (150 million kilometers) away from Earth. Alpha Centauri is the next closest star. It is 25 trillion miles (40 trillion kilometers) away. The Sun is of immense dimensions despite its smallness compared to other stars. It has a diameter of 870,000 miles (1.4 million kilometers) across. This is more than one hundred times the diameter of Earth. The Sun's mass is equal to that of 333,420 Earths. Because of this tremendous mass, the center of the Sun has a pressure of more than one million metric tons per square centimeter.
An object with this much pressure also has a extremely strong gravitational pull. The gravity of the Sun is twenty-eight times stronger than that of Earth. The Sun's gravity is what holds the planets in their orbits.
Although the Sun's mass is so great, and it is so big, the Sun's weight of a standard volume of its matter--its average density, is only 1.4 times the weight of a volume of water. The Earth is 5.5 times denser than water. This can be explained by the density at the core, which is one hundred times denser than water, averaged with the density with the rest of the Sun which is mainly gas in thin layers. This causes the Sun's average density to be so low.
The Sun is powered by nuclear energy in its core. The temperature in the core can reach 25,000,000 degrees F (14,000,000 degrees C) or more. The temperature at the surface is much cooler. It is between 9,000 degrees and 11,000 degrees F (5,000 degrees and 6,000 degrees C).The immense temperature at the core of the Sun causes the fusion of atoms. Four hydrogen atoms are fused together into a single helium atom. This helium atom weighs less than the four hydrogen atoms so there is excess mass. This mass is converted to energy and over time rises to the surface and exits the Sun becoming light rays. These light rays are what reaches Earth and makes life possible here.
The Sun does have an atmosphere. The Sun has several layers. These include, going outward: the nucleus or core, the photosphere, the chromosphere, and the corona. The core is where the Sun's energy is produced and is the hottest part of the Sun. Photosphere means solar surface. The photosphere is less than 1/2,000 of the Sun's radius, only 200 miles thick (320 kilometers) deep. The photosphere is the deepest visible part of the Sun. After the photosphere is the chromosphere. The chromosphere, or "sphere of color" is the lower layer of the atmosphere. The chromosphere extends 7,500 miles (12,000 kilometers) above the surface of the sun. Above the chromosphere is the corona. The corona is like a halo around the sun. It can only be seen during a total eclipse when the photosphere is covered by the moon. Since it is difficult to see the corona, astronomers who study the Sun use a special instrument to view it. This instrument is called a coronagraph. The coronagraph works by producing an artificial eclipse.
The Sun is very active. Its outer edge is always moving and it spins on its axis. We known this from observing sunspots, or cooler areas on the chromosphere. These sunspots appear all over the Sun, usually in pairs and can affect our weather here on Earth. During an eleven year cycle, there are peaks and drops in the number of sunspots on the Sun. When there are many, there is usually many severe storms occurring on Earth, and when there are few, the weather is relatively calm on Earth. From the sunspots erupt solar flares. These are great eruptions of hot gas that shoot outward into space from the sun. They usually occur near sunspots. Near sunspots prominences, or huge arches of hot gas, can erupt and form giant arches larger than Earth from one pair of sunspots to another. There is also the solar wind, which is particles of energy given off from the Sun, that can affect Earth by causing the Northern Lights, or Aurora Borealis.
Core . . . . . . . . . .25,000,000 degrees F(14,000,000 degrees C)
Chromosphere . . .
Inner. . . . . . . . . .9,000 degrees F(5,000 degrees C) to 18,000 degrees F(10,000 degrees C)
Outer. . . . . . . . . .18,000 degrees F(10,000 degrees C) to 180,000 degrees F(100,700 degrees C)
Corona. . . . . . . . .3,600,000 degrees F(2,000,000 degrees C)
The corona of the Sun also has a temperature that is far hotter than the other layers although it is so far from the core of the Sun. An explanation of this is that strong shock waves, which are caused by turbulent movements of the photosphere, intensely heat the very thin gases of the corona.
Class . . . . . . . . . . . . . . . . . . . . . . . . yellow, average star
Diameter. . . . . . . . . . . . . . . . . . . . . . 870,000 miles (1.4 million kilometers)
Distance from Earth . . . . . . . . . . . . . . 93 million miles (150 million kilometers)
Mass . . . . . . . . . . . . . . . . . . . . . . . . equal to 333,420 Earths
Average density. . . . . . . . . . . . . . . . . 1.4 times that of water
Credits: Photographs; "Courtesy Jet Propulsion Laboratory. Copyright (c) California Institute of Technology, Pasadena, CA. All rights reserved. Based on government-sponsored research under contract NAS7-1260."