Sun
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This article is about the star. For other uses, see Sun (disambiguation).
 | |
| Observation data | |
|---|---|
| Mean distance from Earth | 1.496×108 km 8 min 19 s at light speed |
| Visual brightness (V) | −26.74 [1] |
| Absolute magnitude | 4.83 [1] |
| Spectral classification | G2V |
| Metallicity | Z = 0.0177 [2] |
| Angular size | 31.6′ – 32.7′ [3] |
| 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) 396.5±3.0 km/s[4] (relative to the cosmic microwave background) |
| Physical characteristics | |
| Mean diameter | 1.392×106 km [1] 109 × Earth |
| Equatorial radius | 6.955×105 km [5] 109 × Earth[5] |
| Equatorial circumference | 4.379×106 km [5] 109 × Earth[5] |
| Flattening | 9×10−6 |
| Surface area | 6.0877×1012 km2 [5] 11,990 × Earth[5] |
| Volume | 1.412×1018 km3 [5] 1,300,000 × Earth |
| Mass | 1.9891×1030 kg [1] 332,900 × Earth[5] |
| Average density | 1.408×103 kg/m3 [1][5][6] |
| Different Densities | Core: 1.5×105 kg/m3 lower Photosphere: 2×10−4 kg/m3 lower Chromosphere: 5×10−6 kg/m3 Avg. Corona: 1×10−12 kg/m3 [7] |
| Equatorial surface gravity | 274.0 m/s2 [1] 27.94 g 28 × Earth[5] |
| Escape velocity (from the surface) | 617.7 km/s [5] 55 × Earth[5] |
| Temperature of core | ~15.7×106 K [1] |
| Temperature of surface (effective) | 5,778 K [1] |
| Temperature of corona | ~5×106 K |
| Luminosity (Lsol) | 3.846×1026 W [1] ~3.75×1028 lm ~98 lm/W efficacy |
| Mean Intensity (Isol) | 2.009×107 W·m−2·sr−1 |
| Rotation characteristics | |
| Obliquity | 7.25° [1] (to the ecliptic) 67.23° (to the galactic plane) |
| Right ascension of North pole[8] | 286.13° 19h 4min 30s |
| Declination of North pole | +63.87° 63°52' North |
| Sidereal rotation period (at equator) | 25.05 days [1] |
| (at 16° latitude) | 25.38 days [1] 25d 9h 7min 13s [8] |
| (at poles) | 34.3 days [1] |
| Rotation velocity (at equator) | 7.189×103 km/h [5] |
| Photospheric composition (by mass) | |
| Hydrogen | 73.46%[9] |
| Helium | 24.85% |
| Oxygen | 0.77% |
| Carbon | 0.29% |
| Iron | 0.16% |
| Sulfur | 0.12% |
| Neon | 0.12% |
| Nitrogen | 0.09% |
| Silicon | 0.07% |
| Magnesium | 0.05% |
The Sun's color is white, although from the surface of the Earth it may appear yellow because of atmospheric scattering.[12] Its stellar classification, based on spectral class, is G2V, and is informally designated a yellow star, because most of its radiation is in the yellow-green portion of the visible spectrum.[13] In this spectral class label, G2 indicates its surface temperature of approximately 5,778 K (5,505 °C; 9,941 °F), and V (Roman five) 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 430–600 million tons of hydrogen each second. Once regarded by astronomers as a small and relatively insignificant star, the Sun is now presumed to be brighter than about 85% of the stars in the Milky Way galaxy, most of which are red dwarfs.[14][15] 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.[16][17] The Sun's hot corona continuously expands in space creating the solar wind, a hypersonic 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.[18][19]
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 4th in mass.[20] 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 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.[21]
The mean distance of the Sun from the Earth is approximately 149.6 million kilometers (1 AU), though this varies as the Earth moves from perihelion in January to aphelion in July.[22] 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,[23] 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.
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