User:Avaloncloud/sandbox

The Sun (aka amazingphil on youtube go subscribe xx #getphilto3mil) in visible wavelength with filtered white light on 8 July 2014. Characteristic limb darkening and numerous sunspots are visible. 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 = 0.0122[2] Angular size	31.6–32.7′[3] Adjectives	Solar Orbital characteristics Mean distance from Milky Way core	≈ 2.7×1017 km 27200 light-years Galactic period	(2.25–2.50)×108 a Velocity	≈ 220 km/s (orbit around the center of the Milky Way) ≈ 20 km/s (relative to average velocity of other stars in stellar neighborhood) ≈ 370 km/s[4] (relative to the cosmic microwave background) Physical characteristics Equatorial radius	696342±65 km[5] 109 × Earth[6] Equatorial circumference	4.379×106 km[6] 109 × Earth[6] Flattening	9×10−6 Surface area	6.09×1012 km2[6] 12000 × Earth[6] Volume	1.41×1018 km3[6] 1300000 × Earth Mass	(1.98855±0.00025)×1030 kg[1] 333000 × Earth[1] Average density	1.408 g/cm3[1][6][7] 0.255 × Earth[1][6] Center density (modeled)	162.2 g/cm3[1] 12.4 × Earth Equatorial surface gravity	274.0 m/s2[1] 27.94 g 27542.29 cgs 28 × Earth[6] Escape velocity (from the surface)	617.7 km/s[6] 55 × Earth[6] Temperature	Center (modeled): 1.57×107 K[1] Photosphere (effective): 5778 K[1] Corona: ≈ 5×106 K Luminosity (Lsol)	3.846×1026 W[1] ≈ 3.75×1028 lm ≈ 98 lm/W efficacy Mean radiance (Isol)	2.009×107 W·m−2·sr−1 Age	≈4.6 billion years[8][9] Rotation characteristics Obliquity	7.25°[1] (to the ecliptic) 67.23° (to the galactic plane) Right ascension of North pole[10]	286.13° 19 h 4 min 30 s 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] 25 d 9 h 7 min 12 s[10] (at poles)	34.4 days[1] Rotation velocity (at equator)	7.189×103 km/h[6] Photospheric composition (by mass) Hydrogen	73.46%[11] 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% The Sun[a] is the star at the center of the Solar System and is by far the most important source of energy for life on Earth. It is a nearly perfect spherical ball of hot plasma,[12][13] with internal convective motion that generates a magnetic field via a dynamo process.[14] Its diameter is about 109 times that of Earth, and it has a mass about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System.[15] About three quarters of the Sun's mass consists of hydrogen; the rest is mostly helium, with much smaller quantities of heavier elements, including oxygen, carbon, neon and iron.[16]

The Sun is a G-type main-sequence star (G2V) based on spectral class and it is informally referred to as a yellow dwarf. It formed approximately 4.567 billion[b][17] years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became increasingly hot and dense, eventually initiating nuclear fusion in its core. It is thought that almost all stars form by this process. The Sun is roughly middle age and has not changed dramatically for four billion[b] years, and will remain fairly stable for four billion more. However, after hydrogen fusion in its core has stopped, the Sun will undergo severe changes and become a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury, Venus, and possibly Earth.

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. Earth's movement around the Sun is the basis of the solar calendar, which is the predominant calendar in use today.

Contents [hide] 1 Name and etymology 1.1 Religious aspects 2 Characteristics 3 Sunlight 4 Composition 4.1 Singly ionized iron-group elements 4.2 Isotopic composition 5 Structure 5.1 Core 5.2 Radiative zone 5.3 Tachocline 5.4 Convective zone 5.5 Photosphere 5.6 Atmosphere 5.7 Photons and neutrinos 6 Magnetism and activity 6.1 Magnetic field 6.2 Variation in activity 6.3 Long-term change 7 Life phases 7.1 Formation 7.2 Main sequence 7.3 After core hydrogen exhaustion 8 Motion and location 8.1 Orbit in Milky Way 9 Theoretical problems 9.1 Coronal heating problem 9.2 Faint young Sun problem 10 History of observation 10.1 Early understanding 10.2 Development of scientific understanding 10.3 Solar space missions 11 Observation and effects 12 See also 13 Notes 14 References 15 Further reading 16 External links Name and etymology The English proper noun Sun developed from Old English sunne and may be related to south. Cognates to English sun appear in other Germanic languages, including Old Frisian sunne, sonne, Old Saxon sunna, Middle Dutch sonne, modern Dutch zon, Old High German sunna, modern German Sonne, Old Norse sunna, and Gothic sunnō. All Germanic terms for the Sun stem from Proto-Germanic *sunnōn.[18][19]

The English weekday name Sunday stems from Old English (Sunnandæg; "Sun's day", from before 700) and is ultimately a result of a Germanic interpretation of Latin dies solis, itself a translation of the Greek ἡμέρα ἡλίου (hēméra hēlíou).[20] The Latin name for the Sun, Sol, is widely known but is not common in general English language use; the adjectival form is the related word solar.[21][22] The term sol is also used by planetary astronomers to refer to the duration of a solar day on another planet, such as Mars.[23] A mean Earth solar day is approximately 24 hours, whereas a mean Martian 'sol' is 24 hours, 39 minutes, and 35.244 seconds.[24]

Religious aspects The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna.[19] Scholars theorize that the Sun, as a Germanic goddess, may represent an extension of an earlier Proto-Indo-European Sun deity because of Indo-European linguistic connections between Old Norse Sól, Sanskrit Surya, Gaulish Sulis, Lithuanian Saulė, and Slavic Solntse.[19]

In ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background. The symbol of light was a pagan device adopted by Christians – perhaps the most important one that did not come from Jewish traditions. In paganism, the sun was a source of life, giving warmth and illumination to mankind. It was the center of a popular cult among Romans, who would stand at dawn to catch the first rays of sunshine as they prayed. The celebration of the winter solstice (which influenced Christmas) was part of the Roman cult of the sun. Christian churches were built with an orientation so that the congregation faced toward the sunrise in the East.[25]

Characteristics The Sun is a G-type main-sequence star that comprises about 99.86% of the mass of the Solar System. The Sun has an absolute magnitude of +4.83, estimated to be brighter than about 85% of the stars in the Milky Way, most of which are red dwarfs.[26][27] The Sun is a Population I, or heavy-element-rich,[c] star.[28] The formation of the Sun may have been triggered by shockwaves from one or more nearby supernovae.[29] This is suggested by a high abundance of heavy elements in the Solar System, such as gold and uranium, relative to the abundances of these elements in so-called Population II, heavy-element-poor, stars. These elements could most plausibly have been produced by endothermic nuclear reactions during a supernova, or by transmutation through neutron absorption within a massive second-generation star.[28]

The Sun is by far the brightest object in the sky, with an apparent magnitude of −26.74.[30][31] This is about 13 billion times brighter than the next brightest star, Sirius, which has an apparent magnitude of −1.46. The mean distance of the Sun to Earth is approximately 1 astronomical unit (about 150,000,000 km; 93,000,000 mi), though the distance varies as Earth moves from perihelion in January to aphelion in July.[32] 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[d] on Earth by photosynthesis,[33] and drives Earth's climate and weather.

The Sun does not have a definite boundary, and in its outer parts its density decreases exponentially with increasing distance from its center.[34] For the purpose of measurement, however, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun.[35] By this measure, the Sun is a near-perfect sphere with an oblateness estimated at about 9 millionths,[36] which means that its polar diameter differs from its equatorial diameter by only 10 kilometres (6.2 mi).[37] The tidal effect of the planets is weak and does not significantly affect the shape of the Sun.[38] The Sun rotates faster at its equator than at its poles. This differential rotation is caused by convective motion due to heat transport and the Coriolis force due to the Sun's rotation. In a frame of reference defined by the stars, the rotational period is approximately 25.6 days at the equator and 33.5 days at the poles. Viewed from Earth as it orbits the Sun, the apparent rotational period of the Sun at its equator is about 28 days.[39]