The Sun's mass, radius, surface temperature, luminosity and other characteristics are well-known ( Table 1). The interior of the Sun has long been studied by inference from the observed properties of the entire star, though it is now understood in detail through helioseismology, described below.

Solar structure, behavior, and properties See also: Giant star Molecular cloud Protostar Solar system White dwarf star The Sun has enough hydrogen fuel to last another five billion years before evolving into a type of star called a red giant, sloughing off much of its mass a planetary nebula, and then persisting for many more billions of years as a stellar remnant known as a white dwarf star. This formation process initiated approximately 4.6 billion years ago. Material in a disk around the newly formed Sun started to coalesce into planets, asteroids, and other objects that compose the solar system ( Fig. This process proceeded until the pressure and temperature rose high enough in the protostar's core to ignite thermonuclear fusion, exerting an outward, stabilizing pressure against continued collapse. A resulting spherical object, called a protostar, continued collapsing in on itself. Like all stars, the Sun formed from the gravitational collapse of a relatively small portion of cold gas within a large reservoir of matter known as a molecular cloud. Various solar phenomena, including surface and atmospheric features such as sunspots and the hot corona, are studied and extrapolated to other stars. See also: Astrobiology Energy Energy sources Greenhouse effect Insolation Solar energyīesides its great importance to human life, the Sun is of interest to astronomers because it is the only star close enough for detailed study of its surface structure and localized particle emissions, as well as their relation to fundamental solar physics and astrophysics, more broadly.

Only atomic energy, radioactivity, geothermal heating, and the lunar tides are current nonsolar sources of energy. The Sun is the ultimate source of nearly all the energy utilized by industrial civilizations in the form of water power, fossil fuels, and wind, not to mention direct forms of solar energy through solar panels and heating of fluids from mirrors reflecting sunlight. The light and heat of the Sun, helped by a modest greenhouse effect, make the Earth habitable. See also: Hertzsprung-Russell diagram Spectral type Most stars are cooler and smaller than G class stars, placing the Sun in the upper 5% of stars in its neighborhood with regard to size and temperature. Being a typical dwarf star, the Sun is placed on the so-called main sequence in the Hertzsprung-Russell diagram, which plots luminosity against temperature. The Roman numeral V (“five”) stands for normal stars, known as dwarfs larger stars are known as giants or supergiants. (Credit: Jonathan Kriz/Flickr)Īs a star, the Sun is a typical member of the spectral class G2 V, according to the standard system of classification long used by astronomers. 1 The Sun rising over Bloomingdale, Illinois. See also: Earth Earth rotation and orbital motion Gravitation Matter (physics) Planet Plasma (physics) Solar system Starįig. Appearing as an extremely bright disk in the sky, the Sun is too bright to look at except during sunrise or sunset, when the light must travel through substantially more of Earth's atmosphere to reach an observer ( Fig. Almost all the gas is in atomic form as plasma, a hot, ionized state of matter. The surface temperature of the Sun is about 6000 K (5700☌ or 10,000☏) since solids and liquids do not exist at these temperatures, the Sun is entirely gaseous. The Sun measures 1.4 million km (865,000 mi) in diameter and with a mass 333,000 times that of the Earth. Containing 99.8% of the solar system's mass, the Sun holds all the system's planets and objects under its gravitational sway. The star around which the Earth revolves and the source of our planet's light and heat. The radiation and charged particles hurled into space by solar activity can significantly affect human technologies including satellites and power grids.

Notable transient features generated by the Sun's intense magnetic activity include dark regions of reduced temperature called sunspots, light regions called plages, and loops of plasma called prominences. The three layers of the solar atmosphere are the photosphere (the bottom layer, essentially the Sun's 'surface'), the chromosphere, and the corona. The energy of the Sun is produced by thermonuclear fusion, which converts hydrogen into helium within the solar core. The Sun is the star around which Earth revolves and whose light and heat make our planet habitable.Īs a globe of heated, ionized gas known as plasma, the Sun contains 99.8% of the solar system's mass and holds all the system's planets and objects under its gravitational sway.

Gas of sun corona