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Sun

The Sun Observation data Mean distance from Earth 1.496×108 km 8 min 19 s at light speed Visual brightness (V) -26.74 Absolute magnitude 4.83 Spectral classification G2V Metallicity Z = 0.0122 Angular size 31.6' – 32.7' Adjectives solar Orbital characteristics Mean distance from Milky Way core ~2.5×1017 km 26,000 light-years Galactic period (2.25–2.50)×108 a Velocity ~220 km/s (orbit around the center of the Galaxy) ~20 km/s (relative to average velocity of other stars in stellar neighborhood) ~370 km/s (relative to the cosmic microwave background) Physical characteristics Mean diameter 1.392×106 km 109 × Earth Equatorial radius 6.955×105 km 109 × Earth Equatorial circumference 4.379×106 km 109 × Earth Flattening 9×10-6 Surface area 6.0877×1012 km2 11,990 × Earth Volume 1.412×1018 km3 1,300,000 × Earth Mass 1.9891×1030 kg 333,000 × Earth Average density 1.408×103 kg/m3 Density Center (model): 1.622×105 kg/m3 Lower photosphere: 2×10-4 kg/m3 Lower chromosphere: 5×10-6 kg/m3 Corona (avg.): 1×10-12 kg/m3 Equatorial surface gravity 274.0 m/s2 27.94 g 28 × Earth Escape velocity (from the surface) 617.7 km/s 55 × Earth Temperature Center (modeled): ~1.57×107 K Photosphere (effective): 5,778 K Corona: ~5×106 K Luminosity (Lsol) 3.846×1026 W ~3.75×1028 lm ~98 lm/W efficacy Mean Intensity (Isol) 2.009×107 W·m-2·sr-1 Rotation characteristics Obliquity 7.25° (to the ecliptic) 67.23° (to the galactic plane) Right ascension of North pole 286.13° 19h 4min 30s Declination of North pole +63.87° 63°52' North Sidereal rotation period (at equator) 25.05 days (at 16° latitude) 25.38 days 25d 9h 7min 12s (at poles) 34.4 days Rotation velocity (at equator) 7.189×103 km/h Photospheric composition (by mass) Hydrogen 73.46% Helium 24.85% Oxygen 0.77% Carbon 0.29% Iron 0.16% Neon 0.12% Nitrogen 0.09% Silicon 0.07% Magnesium 0.05% Sulfur 0.04% This box: view talk edit The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields. It has a diameter of about 1,392,000 km, about 109 times that of Earth, and its mass (about 2×1030 kilograms, 330,000 times that of Earth) accounts for about 99.86% of the total mass of the Solar System.Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. The rest of it (1.69%, 5,628 times the mass of Earth) consists of heavier elements, including oxygen, carbon, neon, iron, and others.The Sun's stellar classification, based on spectral class, is G2V, and is informally designated as a yellow dwarf, because its visible radiation is most intense in the yellow-green portion of the spectrum and although its color is white, from the surface of the Earth it may appear yellow because of atmospheric scattering of blue light.In the spectral class label, G2 indicates its surface temperature of approximately 5778 K (5505 °C), and V indicates that the Sun, like most stars, is a main-sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses 620 million metric tons of hydrogen each second. Once regarded by astronomers as a small and relatively insignificant star, the Sun is now thought to be brighter than about 85% of the stars in the Milky Way galaxy, most of which are red dwarfs. The absolute magnitude of the Sun is +4.83; however, as the star closest to Earth, the Sun is the brightest object in the sky with an apparent magnitude of -26.74. The Sun's hot corona continuously expands in space creating the solar wind, a stream of charged particles that extends to the heliopause at roughly 100 astronomical units. The bubble in the interstellar medium formed by the solar wind, the heliosphere, is the largest continuous structure in the Solar System.The Sun is currently traveling through the Local Interstellar Cloud in the Local Bubble zone, within the inner rim of the Orion Arm of the Milky Way galaxy. Of the 50 nearest stellar systems within 17 light-years from Earth (the closest being a red dwarf named Proxima Centauri at approximately 4.2 light years away), the Sun ranks fourth in mass.The Sun orbits the center of the Milky Way at a distance of approximately 24,000–26,000 light years from the galactic center, completing one clockwise orbit, as viewed from the galactic north pole, in about 225–250 million years. Since our galaxy is moving with respect to the cosmic microwave background radiation (CMB) in the direction of the constellation Hydra with a speed of 550 km/s, the Sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo.The mean distance of the Sun from the Earth is approximately 149.6 million kilometers (1 AU), though the distance varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds. The energy of this sunlight supports almost all life on Earth by photosynthesis, and drives Earth's climate and weather. The enormous effect of the Sun on the Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a deity. An accurate scientific understanding of the Sun developed slowly, and as recently as the 19th century prominent scientists had little knowledge of the Sun's physical composition and source of energy. This understanding is still developing; there are a number of present-day anomalies in the Sun's behavior that remain unexplained. Cite error: There are tags on this page, but the references will not show without a {{Reflist}} template or a tag; see the help page.
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