The Sun

Observation data
Mean distance from Earth	1.496×1011 m 8. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 31 min at light speed
Visual brightness (V)	−26. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 74m [1]
Absolute magnitude	4. In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 83m [1]
Spectral classification	G2V
Metallicity	Z = 0. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen 0177[2]
Angular size	31. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle 6' - 32. 7' [3]
Adjectives	solar
Orbital characteristics
Mean distance from Milky Way core	~2. In Grammar, an adjective is a word whose main syntactic role is to modify a Noun or Pronoun, giving more information about the In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply 5×1020 m 26,000 light-years
Galactic period	2. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter 25–2. 50×108 a
Velocity	~2. In Astronomy, a Julian year (symbol a) is a unit of measurement of Time defined In Physics, velocity is defined as the rate of change of Position. 20×105 m/s (orbit around the center of the Galaxy) ~2×104 m/s (relative to average velocity of other stars in stellar neighborhood)
Physical characteristics
Mean diameter	1.392×109 m [1] 109 Earths
Equatorial radius	6. To help compare different distances this page lists lengths starting at 109 m (1 Gm or 1 million km) Remote Authentication Dial In User Service ( RADIUS) is a networking protocol that provides centralized access authorization and accounting management for people or computers 955×108 m [4] 109 x that of Earth[4]
Equatorial circumference	4.379×109 m [4] 109 x that of Earth[4]
Flattening	9×10−6
Surface area	6.0877×1018 m² [4] 11,990 Earths[4]
Volume	1.4122×1027 m³ [4] 1,300,000 Earths
Mass	1. The circumference is the distance around a closed Curve. Circumference is a kind of Perimeter. To help compare different distances this page lists lengths starting at 109 m (1 Gm or 1 million km) Ellipticity redirects here For the mathematical topic of ellipticity see Elliptic operator. Surface area is the measure of how much exposed Area an object has To help compare sizes of different surface areas we list here areas between 1018 square metres and 1024 square metres i The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically To help compare different Orders of magnitudes this page lists Volumes between one and one thousand cubic gigametre (10^{27} to 10^{30} Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 9891 ×1030 kg[1] 332,946 Earths
Average density	≈1. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 409 ×103 kg/m³[4][1][5]
Different Densities	Core: 1. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 5×105 kg/m³ lower Photosphere: 2×10-4 kg/m³ lower Cromosphere: 5×10-6 kg/m³ Avg. Corona: 10×10-12kg/m³[6]
Equatorial surface gravity	274. The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surface 0 m/s2 [1] 27. 94 g 28 x Earth's surface gravity[4]
Escape velocity (from the surface)	617. g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy 7 km/s [4] 55 x Earths[4]
Temperature of surface (effective)	5,778 K [1]
Temperature of corona	~5×106 K
Temperature of core	~15. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily 7×106 K [1]
Luminosity (Lsol)	3. Luminosity has different meanings in several different fields of science 846×1026 W [1] ~3. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. 75×1028 lm ~98 lm/W efficacy
Mean Intensity (Isol)	2. The lumen (symbol lm) is the SI unit of Luminous flux, a measure of the perceived power of Light. Luminous efficacy is a property of Light sources which indicates what portion of the emitted Electromagnetic radiation is usable for human vision. Radiance and spectral radiance are radiometric measures that describe the amount of light that passes through or is emitted from a particular area and falls 009×107 W m-2 sr-1
Rotation characteristics
Obliquity	7. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 25° [1] (to the ecliptic) 67. The ecliptic is the apparent path that the Sun traces out in the sky during the year 23° (to the galactic plane)
Right ascension of North pole[7]	286. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere 13° 19 h 4 min 30 s
Declination of North pole	+63. In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either 87° 63°52' North
Sidereal Rotation period (at 16° latitude)	25. Solar rotation can vary because the Sun is composed of a gaseous plasma, and therefore may lack a fixed Rotation rate 38 days [1] 25 d 9 h 7 min 13 s[7]
(at equator)	25. 05 days [1]
(at poles)	34. 3 days [1]
Rotation velocity (at equator)	7. 284 ×103 km/h
Photospheric composition (by mass)
Hydrogen	73. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 46 %[8]
Helium	24. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical 85 %
Oxygen	0. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 77 %
Carbon	0. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 29 %
Iron	0. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 16 %
Sulfur	0. Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 12 %
Neon	0. Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 12 %
Nitrogen	0. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 09 %
Silicon	0. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 07 %
Magnesium	0. Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 05 %
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The Sun is the star at the center of the Solar System. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The Earth and other matter (including other planets, asteroids, meteoroids, comets, and dust) orbit the Sun,^[9] which by itself accounts for about 99. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star 8% of the Solar System's mass. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Energy from the Sun, in the form of sunlight and heat, supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of

The surface of the Sun consists of hydrogen (about 74% of its mass, or 92% of its volume), helium (about 24-25% of mass,^[10] 7% of volume), and trace quantities of other elements, including iron, nickel, oxygen, silicon, sulfur, magnesium, carbon, neon, calcium, and chromium. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 ^[11] The Sun has a spectral class of G2V. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics G2 means that it has a surface temperature of approximately 5,780 K, giving it a white color which, because of atmospheric scattering, appears yellow as seen from the surface of the Earth. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Color temperature is a characteristic of Visible light that has important applications in lighting photography videography publishing and other fields Scattering is a general physical process whereby some forms of Radiation, such as Light, Sound or moving particles for example are forced to deviate from This is a subtractive effect, as the preferential scattering of blue light (causing the sky color) removes enough blue light to leave a residual reddishness that is perceived as yellow. Rayleigh scattering (named after Lord Rayleigh) is the elastic Scattering of Light or other electromagnetic radiation by particles much smaller (When low enough in the sky, the Sun appears orange or red, due to this scattering. )

Its spectrum contains lines of ionized and neutral metals as well as very weak hydrogen lines. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared The V (Roman five) in the spectral class indicates that the Sun, like most stars, is a main sequence star. Roman numerals are a Numeral system originating in ancient Rome, adapted from Etruscan numerals. The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness This means that it generates its energy by nuclear fusion of hydrogen nuclei into helium. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical There are more than 100 million G2 class stars in our galaxy. Once regarded as a small and relatively insignificant star, the Sun is now known to be brighter than 85% of the stars in the galaxy, most of which are red dwarfs. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool Star, of the Main sequence, either late K ^[12]

The Sun orbits the center of the Milky Way galaxy at a distance of approximately 26,000 light-years from the galactic center, completing one revolution in about 225–250 million years. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by The Galactic Center is the rotational center of the Milky Way Galaxy. Its approximate orbital speed is 220 kilometers per second, plus or minus 20 km/s. The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it This is equivalent to about one light-year every 1,400 years, and about one AU every 8 days. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the These measurements of galactic distance and speed are as accurate as we can get given our current knowledge, but will change as we learn more. ^[13]

The Sun is currently traveling through the Local Interstellar Cloud in the low-density Local Bubble zone of diffuse high-temperature gas, in the inner rim of the Orion Arm of the Milky Way Galaxy, between the larger Perseus and Sagittarius arms of the galaxy. The Local Interstellar Cloud, casually called the Local Fluff, is the Interstellar cloud (roughly 30 light years across through which our Solar system The Local Bubble is a cavity in the Interstellar medium (ISM of the Orion Arm of the Milky Way. The Orion Arm is a minor Spiral arm of the Milky Way galaxy The Solar System and Earth are within the Orion Arm The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply The Perseus Spiral Arm is a major Spiral arm of the Milky Way galaxy The Sagittarius Arm (also known as Sagittarius-Carina Arm; labeled "-I" is generally thought to be one of the Spiral arms of our home Galaxy Of the 50 nearest stellar systems within 17 light years from the Earth, the Sun ranks 4th in absolute magnitude as a fourth magnitude star (M=4. This list of stars nearest to the Earth is ordered by increasing distance out to a maximum of 5 Parsecs (16 In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 83).

Overview

The Sun is a Population I, or heavy element-rich^[14], star. In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen ^[15] The formation of the Sun may have been triggered by shockwaves from one or more nearby supernovae. A supernova (plural supernovae or supernovas) is a stellar Explosion. ^[16] This is suggested by a high abundance of heavy elements such as gold and uranium in the solar system relative to the abundances of these elements in so-called Population II (heavy element-poor) stars. See also Abundances of the elements (data page The abundance of a Chemical element measures how relatively common the element is or how much of the element Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen These elements could most plausibly have been produced by endergonic nuclear reactions during a supernova, or by transmutation via neutron absorption inside a massive second-generation star. Endergonic means absorbing energy in the form of work Its etymology stems from the suffix -ergonic as derived from the Greek root ergon meaning work, Nuclear transmutation is the conversion of one Chemical element or Isotope into another which occurs through Nuclear reactions Natural transmutation occurs This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron.

Sunlight is Earth's primary source of energy. The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 1,370 watts per square meter at a distance of one AU from the Sun (that is, on or near Earth). The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the Sunlight on the surface of Earth is attenuated by the Earth's atmosphere so that less power arrives at the surface—closer to 1,000 watts per directly exposed square meter in clear conditions when the Sun is near the zenith. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium In broad terms the zenith is the direction pointing directly above a particular location ( Perpendicular, Orthogonal) This energy can be harnessed via a variety of natural and synthetic processes—photosynthesis by plants captures the energy of sunlight and converts it to chemical form (oxygen and reduced carbon compounds), while direct heating or electrical conversion by solar cells are used by solar power equipment to generate electricity or to do other useful work. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Plants are living Organisms belonging to the kingdom Plantae. A solar cell or photovoltaic cell is a device that converts Solar energy into Electricity by the photovoltaic effect. Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life The energy stored in petroleum and other fossil fuels was originally converted from sunlight by photosynthesis in the distant past. Petroleum ( L petroleum, from Greek πετρέλαιον, lit Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy.

Ultraviolet light from the Sun has antiseptic properties and can be used to sanitize tools and water. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Antiseptics (from Greek αντί - anti, '"against" + σηπτικός - septikos, "putrefactive" are antimicrobial It also causes sunburn, and has other medical effects such as the production of Vitamin D. A sunburn is a burn to living tissue such as Skin produced by overexposure to Ultraviolet (UV radiation commonly from the Sun 's rays Vitamin D is a group of fat-soluble Prohormones, the two major forms of which are vitamin D2 (or Ergocalciferol) and vitamin D3 (or Ultraviolet light is strongly attenuated by Earth's ozone layer, so that the amount of UV varies greatly with latitude and has been responsible for many biological adaptations, including variations in human skin color in different regions of the globe. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Human skin color can range from almost black (due to very high concentrations of the dark brown pigment melanin to nearly colorless (appearing reddish white due to the Blood ^[17]

Observed from Earth, the Sun's path across the sky varies throughout the year. The shape described by the Sun's position, considered at the same time each day for a complete year, is called the analemma and resembles a figure 8 aligned along a north/south axis. Analemma was also a book by Ptolemy. In Astronomy, an analemma ( IPA: /ˌænəˈlɛmə/ Latin for the pedestal of a While the most obvious variation in the Sun's apparent position through the year is a north/south swing over 47 degrees of angle (because of the 23. 5-degree tilt of the Earth with respect to the Sun), there is an east/west component as well, caused by the acceleration of the Earth as it approaches its perihelion with the Sun, and the reduction in the Earth's speed as it moves away to approach its aphelion. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from The north/south swing in apparent angle is the main source of seasons on Earth. A season is one of the major divisions of the Year, generally based on yearly periodic changes in Weather.

The Sun is a magnetically active star. It supports a strong, changing magnetic field that varies year-to-year and reverses direction about every eleven years around solar maximum. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges The Sun's magnetic field gives rise to many effects that are collectively called solar activity, including sunspots on the surface of the Sun, solar flares, and variations in solar wind that carry material through the Solar System. Solar variations are changes in the amount of Solar radiation emitted by the Sun. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. Effects of solar activity on Earth include auroras at moderate to high latitudes, and the disruption of radio communications and electric power. Electric power is defined as the rate at which Electrical energy is transferred by an Electric circuit. Solar activity is thought to have played a large role in the formation and evolution of the Solar System. The formation and evolution of the Solar System is estimated to have begun The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Solar activity changes the structure of Earth's outer atmosphere. The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation

Although it is the nearest star to Earth and has been intensively studied by scientists, many questions about the Sun remain unanswered. Current topics of scientific inquiry include the Sun's regular cycle of sunspot activity, the physics and origin of flares and prominences, the magnetic interaction between the chromosphere and the corona, and the origin (propulsion source) of solar wind. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares A prominence is a large bright feature extending outward from the Sun's surface often in a loop configuration The chromosphere (literally "colour sphere" is a thin layer of the Sun 's atmosphere just above the Photosphere, roughly 10000 kilometres deep A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun.

Location within the galaxy

The Sun lies close to the inner rim of the Milky Way Galaxy's Orion Arm, in the Local Fluff or the Gould Belt, at a hypothesized distance of 7. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply The Orion Arm is a minor Spiral arm of the Milky Way galaxy The Solar System and Earth are within the Orion Arm The Local Interstellar Cloud, casually called the Local Fluff, is the Interstellar cloud (roughly 30 light years across through which our Solar system The Gould Belt is a partial ring of Stars about 3000 Light years across tilted toward the Galactic plane by about 16 to 20 degrees 62±0. 32 kpc from the Galactic Center. History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 The Galactic Center is the rotational center of the Milky Way Galaxy. ^{[18][19][20][21]} The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years. The Perseus Spiral Arm is a major Spiral arm of the Milky Way galaxy ^[22] The Sun, and thus the Solar System, is found in what scientists call the galactic habitable zone. In Astronomy a habitable zone ( HZ) is a region of space where conditions are favorable for Life as it may be found on Earth.

The Apex of the Sun's Way, or the solar apex, is the direction that the Sun travels through space in the Milky Way. The solar apex, or the Apex of the Sun's Way refers to the direction that the Sun travels through space The general direction of the Sun's galactic motion is towards the star Vega near the constellation of Hercules, at an angle of roughly 60 sky degrees to the direction of the Galactic Center. Vega (α Lyr / α Lyrae / Alpha Lyrae ( or) is the brightest Star in the Constellation Lyra, the fifth brightest star in the night Hercules (ˈhɝkjəliːz ˈhɝkjuːliːz is the fifth largest of the 88 modern Constellations It was also one of Ptolemy 's 48 constellations The Galactic Center is the rotational center of the Milky Way Galaxy. The Sun's orbit around the Galaxy is expected to be roughly elliptical with the addition of perturbations due to the galactic spiral arms and non-uniform mass distributions. In addition the Sun oscillates up and down relative to the galactic plane approximately 2. 7 times per orbit. This is very similar to how a simple harmonic oscillator works with no drag force (damping) term. This article is about the harmonic oscillator in classical mechanics Due to the greater density of stars close to the galactic plane, these oscillations often coincide with mass extinction periods on earth, presumably due to increased impact events. An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period See also Impact crater An impact event is the Collision of a large Meteoroid, Asteroid or Comet (generically ^[23]

It takes the Solar System about 225–250 million years to complete one orbit of the galaxy (a galactic year),^[24] so it is thought to have completed 20–25 orbits during the lifetime of the Sun and 1/1250th of a revolution since the origin of humans. The galactic year, also known as a cosmic year, is the duration of time required for the Solar system to Orbit once around the center of the Milky Human evolution, or anthropogenesis, is the part of biological Evolution concerning the emergence of Homo sapiens as a distinct Species The orbital speed of the Solar System about the center of the Galaxy is approximately 220 km/s. The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it At this speed, it takes around 1400 years for the Solar System to travel a distance of 1 light-year, or 8 days to travel 1 AU. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the ^[25]

Life cycle

Main articles: Formation and evolution of the solar system and Stellar evolution

The Sun's current main sequence age, determined using computer models of stellar evolution and nucleocosmochronology, is thought to be about 4. The formation and evolution of the Solar System is estimated to have begun Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness A computer simulation, a computer model or a computational model is a Computer program, or network of computers that attempts to simulate an Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime Nucleocosmochronology, also known as cosmochronology, is a relatively new technique used to determine timescales for astrophysical objects and events 57 billion years. ^[26]

It is thought that about 4. 59 billion years ago, the rapid collapse of a hydrogen molecular cloud led to the formation of a third generation T Tauri Population I star, the Sun. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 See also Solar nebula A molecular cloud, sometimes called a stellar nursery if Star formation is occurring within is a type of Interstellar T Tauri stars ( TTS) are a class of variable Stars named after their prototype – T Tauri. In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen The nascent star assumed a nearly circular orbit about 26,000 light-years from the centre of the Milky Way Galaxy. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply ^[27]

The Sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in Stars to build the nuclei of the heavier elements. Each second, more than 4 million tonnes of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation; at this rate, the Sun will have so far converted around 100 Earth-masses of matter into energy. This article is about the tonne or metric ton For other tons see Ton. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost The Sun will spend a total of approximately 10 billion years as a main sequence star.

The Sun does not have enough mass to explode as a supernova. A supernova (plural supernovae or supernovas) is a stellar Explosion. Instead, in 5–6 billion years, it will enter a red giant phase, its outer layers expanding as the hydrogen fuel in the core is consumed and the core contracts and heats up. A red giant is a luminous Giant star of low or intermediate mass (roughly 0 Helium fusion will begin when the core temperature reaches around 100 million K and will produce carbon, entering the asymptotic giant branch phase. Helium fusion is a kind of Nuclear fusion, with the nuclei involved being Helium. The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass Stars This is a period of Stellar evolution ^[15]

Life-cycle of the Sun; sizes are not drawn to scale.

Earth's fate is not clear. As a red giant, the Sun will have a maximum radius beyond the Earth's current orbit, 1 AU (150,000,000,000 m), 250 times the present radius of the Sun. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International ^[28] However, by the time it is an asymptotic giant branch star, the Sun will have lost roughly 30% of its present mass due to a stellar wind, so the orbits of the planets will move outward. A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a Star. If it were only for this, Earth would probably be spared, but new research suggests that Earth will be swallowed by the Sun due to tidal interactions. ^[28] Even if Earth escapes incineration in the Sun, its water will be boiled away and most of its atmosphere would escape into space. In fact, even during its life in the main sequence the Sun is gradually becoming more luminous, its surface temperature slowly rising. The increase in solar temperatures is such that in about 900 million years, the surface of the Earth will become too hot for the survival of life as we know it. ^[29] After another billion years the surface water will have completely disappeared. ^[30]

Following the red giant phase, intense thermal pulsations will cause the Sun to throw off its outer layers, forming a planetary nebula. A planetary nebula is an Emission nebula consisting of a glowing shell of Gas and plasma formed by certain types of Stars when they die The only object that will remain after the outer layers are ejected is the extremely hot stellar core, which will slowly cool and fade as a white dwarf over many billions of years. A white dwarf, also called a degenerate dwarf, is a small Star composed mostly of Electron-degenerate matter. This stellar evolution scenario is typical of low- to medium-mass stars. Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime ^[31][32]

Structure

An illustration of the structure of the Sun

The Sun is a yellow dwarf star comprising about 99% of the total mass of the solar system. It is a near-perfect sphere, with an oblateness estimated at about 9 millionths,^[33] which means that its polar diameter differs from its equatorial diameter by only 10 km (6 mi). "Globose" redirects here See also Globose nucleus. A sphere (from Greek σφαίρα - sphaira, "globe Ellipticity redirects here For the mathematical topic of ellipticity see Elliptic operator. As the Sun exists in a plasmatic state and is not solid, it rotates faster at its equator than at its poles. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the The Polish people, or Poles, (Polacy) are a Western Slavic Ethnic group of Central Europe, living predominantly in Poland. This behaviour is known as differential rotation. Solar rotation can vary because the Sun is composed of a gaseous plasma, and therefore may lack a fixed Rotation rate The period of this actual rotation is approximately 25 days at the equator and 35 days at the poles. However, due to our constantly changing vantage point from the Earth as it orbits the Sun, the apparent rotation of the star at its equator is about 28 days. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The centrifugal effect of this slow rotation is 18 million times weaker than the surface gravity at the Sun's equator. The tidal effect of the planets is even weaker, and does not significantly affect the shape of the Sun.

The Sun does not have a definite boundary as rocky planets do, and in its outer parts the density of its gases drops approximately exponentially with increasing distance from its center. WikipediaWikiProject Probability#Standards for a discussionof standards used for probability distribution articles such as this one Nevertheless, it has a well-defined interior structure, described below. The Sun's radius is measured from its center to the edge of the photosphere. This is simply the layer above which the gases are too cool or too thin to radiate a significant amount of light, and is therefore the surface most readily visible to the naked eye. The naked eye is a Figure of speech referring to human Visual perception that is unaided by enhancing equipment such as a Telescope or The solar core comprises 10 percent of its total volume, but 40 percent of its total mass. ^[34]

The solar interior is not directly observable, and the Sun itself is opaque to electromagnetic radiation. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. However, just as seismology uses waves generated by earthquakes to reveal the interior structure of the Earth, the discipline of helioseismology makes use of pressure waves (infrasound) traversing the Sun's interior to measure and visualize the star's inner structure. Seismology (from Greek grc σεισμός seismos, "earthquake" and grc -λογία -logia) is the scientific study of Earthquakes An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer Helioseismology is the study of the propagation of Pressure waves in the Sun. Infrasound is Sound with a Frequency too low to be heard by the human Ear. Computer modeling of the Sun is also used as a theoretical tool to investigate its deeper layers. A computer simulation, a computer model or a computational model is a Computer program, or network of computers that attempts to simulate an

Core

Cross-section of a solar-type star. (NASA)

The core of the Sun is considered to extend from the center to about 0. The core of the Sun is considered to extend from the center to about 0 2 solar radii. It has a density of up to 150,000 kg/m³ (150 times the density of water on Earth) and a temperature of close to 13,600,000 kelvin (by contrast, the surface of the Sun is around 5,800 kelvin). The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Recent analysis of SOHO mission data favors a faster rotation rate in the core than in the rest of the radiative zone. The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December ^[35] Through most of the Sun's life, energy is produced by nuclear fusion through a series of steps called the p–p (proton–proton) chain; this process converts hydrogen into helium. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus The proton-proton chain reaction is one of several fusion reactions by which Stars convert Hydrogen to Helium, the primary alternative being the Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical The core is the only location in the Sun that produces an appreciable amount of heat via fusion: the rest of the star is heated by energy that is transferred outward from the core. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature All of the energy produced by fusion in the core must travel through many successive layers to the solar photosphere before it escapes into space as sunlight or kinetic energy of particles. Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. The kinetic energy of an object is the extra Energy which it possesses due to its motion

About 3. 4×10³⁸ protons (hydrogen nuclei) are converted into helium nuclei every second (out of ~8. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive 9×10⁵⁶ total amount of free protons in the Sun), releasing energy at the matter–energy conversion rate of 4. 26 million tonnes per second, 383 yottawatts (3. This article is about the tonne or metric ton For other tons see Ton. yotta- (symbol Y) is an SI prefix in the SI ( System of units) denoting 1024 or 1 000 000 000 000 000 000 000 000 The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. 83×10²⁶ W) or 9. 15×10¹⁰ megatons of TNT per second. Trinitrotoluene ( TNT) is a Chemical compound with the formula C6H2(NO23CH3 This actually corresponds to a surprisingly low rate of energy production in the Sun's core—about 0. 3 µW/cm³ (microwatts per cubic cm), or about 6 µW/kg of matter. For comparison, the human body produces heat at approximately the rate 1. 2 W/kg, roughly a million times greater per unit mass. The use of plasma with similar parameters for energy production on Earth would be completely impractical—even a modest 1 GW fusion power plant would require about 170 billion tonnes of plasma occupying almost one cubic mile. Hence, terrestrial fusion reactors utilize far higher plasma temperatures than those in Sun's interior.

The rate of nuclear fusion depends strongly on density and temperature, so the fusion rate in the core is in a self-correcting equilibrium: a slightly higher rate of fusion would cause the core to heat up more and expand slightly against the weight of the outer layers, reducing the fusion rate and correcting the perturbation; and a slightly lower rate would cause the core to cool and shrink slightly, increasing the fusion rate and again reverting it to its present level. Thermal Expansion is the tendency of matter to change in Volume in response to a change in temperature In the Physical sciences weight is a Measurement of the gravitational Force acting on an object

The high-energy photons (gamma rays) released in fusion reactions are absorbed in only few millimetres of solar plasma and then re-emitted again in random direction (and at slightly lower energy)—so it takes a long time for radiation to reach the Sun's surface. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Estimates of the "photon travel time" range between 10,000 and 170,000 years. ^[36]

After a final trip through the convective outer layer to the transparent "surface" of the photosphere, the photons escape as visible light. Each gamma ray in the Sun's core is converted into several million visible light photons before escaping into space. Neutrinos are also released by the fusion reactions in the core, but unlike photons they rarely interact with matter, so almost all are able to escape the Sun immediately. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost For many years measurements of the number of neutrinos produced in the Sun were lower than theories predicted by a factor of 3. Introduction The Sun is a natural Nuclear fusion reactor powered by a Proton-proton chain reaction which converts four Hydrogen nuclei This discrepancy was recently resolved through the discovery of the effects of neutrino oscillation: the Sun in fact emits the number of neutrinos predicted by the theory, but neutrino detectors were missing 2/3 of them because the neutrinos had changed flavor. Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a Neutrino created with a specific Lepton In Particle physics, flavour or flavor (see spelling differences) is a Quantum number of Elementary particles related to their

Radiative zone

From about 0. 2 to about 0. 7 solar radii, solar material is hot and dense enough that thermal radiation is sufficient to transfer the intense heat of the core outward. Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature. In this zone there is no thermal convection; while the material grows cooler as altitude increases, this temperature gradient is less than the value of adiabatic lapse rate and hence cannot drive convection. Convection in the most general terms refers to the movement of molecules within Fluids (i In atmospheric sciences ( Meteorology, Climatology and related fields the temperature gradient (typically of air, more generally of any Fluid The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere Heat is transferred by radiation—ions of hydrogen and helium emit photons, which travel a brief distance before being reabsorbed by other ions. Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena In this way energy makes its way very slowly (see above) outward.

Between the radiative zone and the convection zone is a transition layer called the tachocline. The tachocline is the transition region of the Sun between the radiative interior and the differentially rotating outer convective zone This is a region where the sharp regime change between the uniform rotation of the radiative zone and the differential rotation of the convection zone results in a large shear -- i. e. a condition where successive vertical layers slide past one another.

Convection zone

Structure of the Sun

In the Sun's outer layer (down to approximately 70% of the solar radius), the solar plasma is not dense enough or hot enough to transfer the heat energy of the interior outward via radiation. As a result, thermal convection occurs as thermal columns carry hot material to the surface (photosphere) of the Sun. A thermal column (or thermal) is a column of rising Air in the lower altitudes of the Earth's atmosphere. Once the material cools off at the surface, it plunges back downward to the base of the convection zone, to receive more heat from the top of the radiative zone. Convective overshoot is thought to occur at the base of the convection zone, carrying turbulent downflows into the outer layers of the radiative zone. Convective overshoot is a phenomenon of Convection carrying material beyond an Unstable region of the Atmosphere into a Stratified, stable region

The thermal columns in the convection zone form an imprint on the surface of the Sun, in the form of the solar granulation and supergranulation. Granules on the Photosphere of the Sun are caused by Convection currents ( Thermal columns Bénard cells) of plasma within Supergranulation is a particular pattern on the Sun surface It was discovered in the 1950s by A The turbulent convection of this outer part of the solar interior gives rise to a "small-scale" dynamo that produces magnetic north and south poles all over the surface of the Sun.

The Sun's thermal columns are Bénard cells and therefore tend to be hexagonal prisms. Bénard cells are Convection cells that appear spontaneously in a liquid layer when heat is applied from below

Photosphere

The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light. Above the photosphere visible sunlight is free to propagate into space, and its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of H^- ions, which absorb visible light easily. Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H^- ions. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 ^[37][38] The photosphere is actually tens to hundreds of kilometers thick, being slightly less opaque than air on Earth. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as limb darkening. Limb darkening refers to the diminishing of intensity in the image of a star as one moves from the center of the image to the edge or " Limb " of the image Sunlight has approximately a black-body spectrum that indicates its temperature is about 6,000 K, interspersed with atomic absorption lines from the tenuous layers above the photosphere. In Physics, a black body is an object that absorbs all light that falls on it The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared The photosphere has a particle density of about 10²³ m⁻³ (this is about 1% of the particle density of Earth's atmosphere at sea level). Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five

During early studies of the optical spectrum of the photosphere, some absorption lines were found that did not correspond to any chemical elements then known on Earth. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. In 1868, Norman Lockyer hypothesized that these absorption lines were because of a new element which he dubbed "helium", after the Greek Sun god Helios. Sir Joseph Norman Lockyer, FRS ( May 17, 1836 &ndash August 16, 1920) was an English scientist and astronomer Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical In Greek mythology the Sun was personified as Helios (ˈhiliˌɑs ( Ἥλιος Latinized as Helius) It was not until 25 years later that helium was isolated on Earth. ^[39]

Atmosphere

Main articles: Corona and Coronal loop

During a total solar eclipse, the solar corona can be seen with the naked eye. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily Coronal loops form the basic structure of the lower Corona and Transition region of the Sun. A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily

The parts of the Sun above the photosphere are referred to collectively as the solar atmosphere. They can be viewed with telescopes operating across the electromagnetic spectrum, from radio through visible light to gamma rays, and comprise five principal zones: the temperature minimum, the chromosphere, the transition region, the corona, and the heliosphere. The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions The chromosphere (literally "colour sphere" is a thin layer of the Sun 's atmosphere just above the Photosphere, roughly 10000 kilometres deep The solar transition region is a region of the Sun 's atmosphere between the Chromosphere and Corona. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the The heliosphere, which may be considered the tenuous outer atmosphere of the Sun, extends outward past the orbit of Pluto to the heliopause, where it forms a sharp shock front boundary with the interstellar medium. The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the For the music album by Converter see Shock Front For the 1977 horror film see Shock Waves A shock wave (also called The chromosphere, transition region, and corona are much hotter than the surface of the Sun. The reason why has not been conclusively proven; evidence suggests that Alfvén waves may have enough energy to heat the corona. An Alfvén wave, named after Hannes Alfvén, is a type of magnetohydrodynamic Wave. ^[40]

The coolest layer of the Sun is a temperature minimum region about 500 km above the photosphere, with a temperature of about 4,000 K. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic This part of the Sun is cool enough to support simple molecules such as carbon monoxide and water, which can be detected by their absorption spectra. Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas.

Above the temperature minimum layer is a thin layer about 2,000 km thick, dominated by a spectrum of emission and absorption lines. It is called the chromosphere from the Greek root chroma, meaning color, because the chromosphere is visible as a colored flash at the beginning and end of total eclipses of the Sun. A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured The temperature in the chromosphere increases gradually with altitude, ranging up to around 100,000 K near the top.

Taken by Hinode's Solar Optical Telescope on January 12, 2007, this image of the Sun reveals the filamentary nature of the plasma connecting regions of different magnetic polarity. Hinode (ひので Japanese: "Sunrise" formerly known as Solar-B, is a Japan Aerospace Exploration Agency Solar mission with Events 475 - Basiliscus becomes Byzantine Emperor, with a coronation ceremony in the Hebdomon palace in Constantinople Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.

Above the chromosphere is a transition region in which the temperature rises rapidly from around 100,000 K to coronal temperatures closer to one million K. The chromosphere (literally "colour sphere" is a thin layer of the Sun 's atmosphere just above the Photosphere, roughly 10000 kilometres deep The solar transition region is a region of the Sun 's atmosphere between the Chromosphere and Corona. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The increase is because of a phase transition as helium within the region becomes fully ionized by the high temperatures. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons The transition region does not occur at a well-defined altitude. Rather, it forms a kind of nimbus around chromospheric features such as spicules and filaments, and is in constant, chaotic motion. A halo (ἅλως also known as a nimbus, icebow or Gloriole) is an Optical phenomenon that appears near or around the Sun or In Solar physics, a spicule is a dynamic jet of about 500km diameter on the Sun. A prominence is a large bright feature extending outward from the Sun's surface often in a loop configuration The transition region is not easily visible from Earth's surface, but is readily observable from space by instruments sensitive to the far ultraviolet portion of the spectrum. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies

The corona is the extended outer atmosphere of the Sun, which is much larger in volume than the Sun itself. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily The corona merges smoothly with the solar wind that fills the solar system and heliosphere. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the The low corona, which is very near the surface of the Sun, has a particle density of 10¹⁴–10¹⁶ m⁻³. (Earth's atmosphere near sea level has a particle density of about 2×10²⁵ m⁻³. ) The temperature of the corona is several million kelvin. While no complete theory yet exists to account for the temperature of the corona, at least some of its heat is known to be from magnetic reconnection. Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another changing their patterns of connectivity with respect to the

The heliosphere extends from approximately 20 solar radii (0. The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the 1 AU) to the outer fringes of the solar system. Its inner boundary is defined as the layer in which the flow of the solar wind becomes superalfvénic—that is, where the flow becomes faster than the speed of Alfvén waves. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. Turbulence and dynamic forces outside this boundary cannot affect the shape of the solar corona within, because the information can only travel at the speed of Alfvén waves. The solar wind travels outward continuously through the heliosphere, forming the solar magnetic field into a spiral shape, until it impacts the heliopause more than 50 AU from the Sun. The Parker spiral is the shape of the Sun 's magnetic field as it extends through the solar system The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the In December 2004, the Voyager 1 probe passed through a shock front that is thought to be part of the heliopause. See also Voyager 1 and Voyager 2. The Voyager program consists of a pair of unmanned scientific probes Voyager 1 and Both of the Voyager probes have recorded higher levels of energetic particles as they approach the boundary. ^[41]

Chemical composition

The Sun is composed of chemical elements. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. Various scientists have analysed these elements to find out their abundances, their relations to planetary elements, and their diffusion (distribution) within the solar interior.

Element abundances

According to Bahcal (1990)^[42] cited in Thoul (1993:15),^[43] the characteristic mass fractions of some elements in the solar interior (r < 0. 7R) are:

• Hydrogen: 34%
• Helium: 64%
• Oxygen: 1%

Lithium, beryllium, and boron

In 1968, a Belgian academic found that the abundances of lithium, beryllium, and boron are higher than previously thought (Grevesse 1968^[44]). Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 In Mathematics, a percentage is a way of expressing a number as a Fraction of 100 ( per cent meaning "per hundred" Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The Kingdom of Belgium is a Country in northwest Europe. It is a founding member of the European Union and hosts its headquarters as well as those Lithium (ˈlɪθiəm is a Chemical element with the symbol Li and Atomic number 3 Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B.

Neon

In 2005, three academics claimed that the neon abundance in the Sun may be higher than previously thought, based on helioseismological observations (Bahcall et al 2005^[45]). Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 Helioseismology is the study of the propagation of Pressure waves in the Sun.

Helium

Until at least 1986 the generally accepted initial helium content of the Sun was Y=0. 25, but two academics in 1986 claimed that the value Y=0. 279 is more correct (Lebreton and Maeder 1986:119^[46]).

Singly-ionised iron group elements

In 1970s, much research focused on the abundances of iron group elements in the Sun(Biemont 1978;^[47] and Ross and Aller 1976, Withbroe 1976, Hauge and Engvold 1977, cited in Biemont 1978^[47]).

The first largely complete set of gf values of singly-ionised iron group elements were made available first by Corliss and Bozman (1962 cited in Biemont 1978^[47]) and Warner (1967 cited in Biemont 1978^[47]), and improved f values were computed by Smith (1976 cited in Biemont 1978^[47]). In 1978 the abundances of singly-ionised elements of the iron group were derived by Biemont (1978^[47]).

The abundance determination of some iron group elements is difficult because of their hyperfine structures, eg cobalt and manganese (Biemont 1978^[47]). Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. Manganese (ˈmæŋgəniːz is a Chemical element, designated by the symbol Mn.

Solar and planetary mass fractionation relationship

Various authors have considered the existence of a mass fractionation relationship between the isotopic compositions of solar and planetary noble gases (Signer and Suess 1963; Manuel 1967; Marti 1969; Kuroda and Manuel 1970; Srinivasan and Manuel 1971, all cited in Manuel and Hwaung 1983^[11]), for example correlations between isotopic compositions of planetary and solar Ne and Xe (Kuroda and Manuel 1970 cited in Manuel and Hwaung 1983:7^[11]). History Noble gas is translated from the German noun de ''Edelgas'' first used in 1898 by Hugo Erdmann to indicate their extremely low level of reactivity Nevertheless, the belief that the whole Sun has the same composition as the solar atmosphere was still widespread, at least until 1983 (Manuel and Hwaung 1983:7^[11]).

In 1983, two academics claimed that it was the fractionation in the Sun itself that caused the fractionation relationship between the isotopic compositions of planetary and solar wind implanted noble gases (Manuel and Hwaung 1983:7^[11]).

Element diffusion

The Sun is composed of chemical elements. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. Of particular scientific interest is the diffusion of these elements inside the Sun, i. e. their distribution inside the star's interior. The diffusion of solar elements is determined by many variables, including gravity, which causes the heavier elements (e. Gravitation is a natural Phenomenon by which objects with Mass attract one another g. helium in absence of other heavier elements) to stick to the centre of the solar mass while the non-heavy elements (e. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical g. hydrogen) diffuse towards the exterior of the Sun (Thoul et al 1993:3). Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 ^[43]

Helium diffusion

Of specialist scientific interest is the diffusion of helium in the solar interior. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical It has been found that the diffusion process of helium speeds up with time (Noerdlinger 1977^[48]).

Composition of the photosphere

The composition of the photosphere, ie the surface layers of the Sun, is usually taken as representative of the chemical composition of the primordial solar system, except for deuterium, lithium, boron, and beryllium (Aller 1968^[49]). Deuterium, also called heavy hydrogen, is a Stable isotope of Hydrogen with a Natural abundance in the Oceans of Earth Lithium (ˈlɪθiəm is a Chemical element with the symbol Li and Atomic number 3 Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B. Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4

Solar cycles

Main article: Sunspots

Sunspots and the sunspot cycle

Measurements of solar cycle variation during the last 30 years. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming

When observing the Sun with appropriate filtration, the most immediately visible features are usually its sunspots, which are well-defined surface areas that appear darker than their surroundings because of lower temperatures. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming Sunspots are regions of intense magnetic activity where convection is inhibited by strong magnetic fields, reducing energy transport from the hot interior to the surface. Convection in the most general terms refers to the movement of molecules within Fluids (i The magnetic field gives rise to strong heating in the corona, forming active regions that are the source of intense solar flares and coronal mass ejections. A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. The largest sunspots can be tens of thousands of kilometers across.

The number of sunspots visible on the Sun is not constant, but varies over an 11-year cycle known as the Solar cycle. The solar cycle, or the solar magnetic activity cycle, is the main source of periodic variation of all solar phenomena driving variations in Space weather. At a typical solar minimum, few sunspots are visible, and occasionally none at all can be seen. Those that do appear are at high solar latitudes. As the sunspot cycle progresses, the number of sunspots increases and they move closer to the equator of the Sun, a phenomenon described by Spörer's law. Spörer's law predicts the variation of Sunspot latitudes during a Solar cycle. Sunspots usually exist as pairs with opposite magnetic polarity. The magnetic polarity of the leading sunspot alternates every solar cycle, so that it will be a north magnetic pole in one solar cycle and a south magnetic pole in the next.

History of the number of observed sunspots during the last 250 years, which shows the ~11-year solar cycle.

The solar cycle has a great influence on space weather, and is a significant influence on the Earth's climate. Space weather is the concept of changing environmental conditions in Outer space. Solar activity minima tend to be correlated with colder temperatures, and longer than average solar cycles tend to be correlated with hotter temperatures. In the 17th century, the solar cycle appears to have stopped entirely for several decades; very few sunspots were observed during this period. During this era, which is known as the Maunder minimum or Little Ice Age, Europe experienced very cold temperatures. The Maunder Minimum is the name given to the period roughly from 1645 to 1715, when Sunspots became exceedingly rare as noted by solar observers of The Little Ice Age (LIA was a period of cooling occurring after a warmer era known as the Medieval Warm Period or Medieval Climate Optimum ^[50] Earlier extended minima have been discovered through analysis of tree rings and also appear to have coincided with lower-than-average global temperatures. Dendrochronology (from Greek grc δένδρον dendron, "tree" grc χρόνος khronos, "time" and grc -λογία

Possible long term cycle

A recent theory claims that there are magnetic instabilities in the core of the Sun which cause fluctuations with periods of either 41,000 or 100,000 years. These could provide a better explanation of the ice ages than the Milankovitch cycles. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets Milankovitch cycles are the collective effect of changes in the Earth 's movements upon its climate named after Serbian civil engineer and Mathematician Like many theories in astrophysics, this theory cannot be tested directly. ^[51][52]

Theoretical problems

Solar neutrino problem

For many years the number of solar electron neutrinos detected on Earth was one third to one half of the number predicted by the standard solar model. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost The Standard Solar Model (SSM is the best current physical model of our Sun. This anomalous result was termed the solar neutrino problem. Introduction The Sun is a natural Nuclear fusion reactor powered by a Proton-proton chain reaction which converts four Hydrogen nuclei Theories proposed to resolve the problem either tried to reduce the temperature of the Sun's interior to explain the lower neutrino flux, or posited that electron neutrinos could oscillate—that is, change into undetectable tau and muon neutrinos as they traveled between the Sun and the Earth. Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a Neutrino created with a specific Lepton Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost ^[53] Several neutrino observatories were built in the 1980s to measure the solar neutrino flux as accurately as possible, including the Sudbury Neutrino Observatory and Kamiokande. The Sudbury Neutrino Observatory ( SNO) is a Neutrino observatory located 6800 feet (about 2 km underground in Vale Inco 's Creighton Mine The is a Neutrino Physics Laboratory located underground in the Mozumi Mine of the Kamioka Mining and Smelting Co Results from these observatories eventually led to the discovery that neutrinos have a very small rest mass and do indeed oscillate. ^[54] Moreover, in 2001 the Sudbury Neutrino Observatory was able to detect all three types of neutrinos directly, and found that the Sun's total neutrino emission rate agreed with the Standard Solar Model, although depending on the neutrino energy as few as one-third of the neutrinos seen at Earth are of the electron type. This proportion agrees with that predicted by the Mikheyev-Smirnov-Wolfenstein effect (also known as the matter effect), which describes neutrino oscillation in matter. The Mikheyev-Smirnov-Wolfenstein effect (often referred to as matter effect) is a Particle physics process which can act to modify Neutrino oscillations Hence, the problem is now resolved.

Coronal heating problem

Main article: Corona

The optical surface of the Sun (the photosphere) is known to have a temperature of approximately 6,000 K. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Above it lies the solar corona at a temperature of 1,000,000 K. The high temperature of the corona shows that it is heated by something other than direct heat conduction from the photosphere. Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower

It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating. The first is wave heating, in which sound, gravitational and magnetohydrodynamic waves are produced by turbulence in the convection zone. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. These waves travel upward and dissipate in the corona, depositing their energy in the ambient gas in the form of heat. The other is magnetic heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in the form of large solar flares and myriad similar but smaller events. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another changing their patterns of connectivity with respect to the A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares ^[55]

Currently, it is unclear whether waves are an efficient heating mechanism. All waves except Alfvén waves have been found to dissipate or refract before reaching the corona. An Alfvén wave, named after Hannes Alfvén, is a type of magnetohydrodynamic Wave. ^[56] In addition, Alfvén waves do not easily dissipate in the corona. Current research focus has therefore shifted towards flare heating mechanisms. One possible candidate to explain coronal heating is continuous flaring at small scales,^[57] but this remains an open topic of investigation.

Faint young Sun problem

Main article: Faint young Sun paradox

Theoretical models of the Sun's development suggest that 3. The faint young Sun paradox or the faint young Sun problem describes the apparent contradiction between observations of liquid Water early in the Earth's history 8 to 2. 5 billion years ago, during the Archean period, the Sun was only about 75% as bright as it is today. Such a weak star would not have been able to sustain liquid water on the Earth's surface, and thus life should not have been able to develop. However, the geological record demonstrates that the Earth has remained at a fairly constant temperature throughout its history, and in fact that the young Earth was somewhat warmer than it is today. The consensus among scientists is that the young Earth's atmosphere contained much larger quantities of greenhouse gases (such as carbon dioxide, methane and/or ammonia) than are present today, which trapped enough heat to compensate for the lesser amount of solar energy reaching the planet. Greenhouse gases are gaseous constituents of the atmosphere bothnatural and anthropogenic that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life ^[58]

Magnetic field

See also: Stellar magnetic field

The heliospheric current sheet extends to the outer reaches of the Solar System, and results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium. A stellar magnetic field is a Magnetic field generated by the motion of conductive plasma inside a Main sequence ( Hydrogen -burning The heliospheric current sheet (HCS is the surface within the Solar System where the polarity of the Sun 's Magnetic field changes from In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound The interplanetary medium is the material which fills the solar system and through which all the larger solar system bodies such as Planets Asteroids ^[59]

All matter in the Sun is in the form of gas and plasma because of its high temperatures. This page is about the physical properties of gas as a state of matter In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound This makes it possible for the Sun to rotate faster at its equator (about 25 days) than it does at higher latitudes (about 35 days near its poles). The differential rotation of the Sun's latitudes causes its magnetic field lines to become twisted together over time, causing magnetic field loops to erupt from the Sun's surface and trigger the formation of the Sun's dramatic sunspots and solar prominences (see magnetic reconnection). Solar rotation can vary because the Sun is composed of a gaseous plasma, and therefore may lack a fixed Rotation rate In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges Coronal loops form the basic structure of the lower Corona and Transition region of the Sun. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming A prominence is a large bright feature extending outward from the Sun's surface often in a loop configuration Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another changing their patterns of connectivity with respect to the This twisting action gives rise to the solar dynamo and an 11-year solar cycle of magnetic activity as the Sun's magnetic field reverses itself about every 11 years. The solar dynamo is the physical process that generates the Sun 's Magnetic field.

The influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium creates the heliospheric current sheet, which separates regions with magnetic fields pointing in different directions. The interplanetary medium is the material which fills the solar system and through which all the larger solar system bodies such as Planets Asteroids The heliospheric current sheet (HCS is the surface within the Solar System where the polarity of the Sun 's Magnetic field changes from The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth. If space were a vacuum, then the Sun's 10^-4 tesla magnetic dipole field would reduce with the cube of the distance to about 10^-11 tesla. The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic But satellite observations show that it is about 100 times greater at around 10^-9 tesla. Magnetohydrodynamic (MHD) theory predicts that the motion of a conducting fluid (such as the interplanetary medium) in a magnetic field induces electric currents, which in turn generate magnetic fields, and in this respect it behaves like an MHD dynamo. Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically The MHD ( magnetohydrodynamic) generator or dynamo transforms Thermal energy or Kinetic energy directly into Electricity

History of observation

Early understanding

The Trundholm Sun chariot pulled by a horse is a sculpture believed to be illustrating an important part of Nordic Bronze Age mythology. The Trundholm sun chariot ( Danish: Solvognen) is a late Nordic Bronze Age artifact discovered in Denmark, that has been interpreted as a depiction The Nordic Bronze Age (also Northern Bronze Age) is the name given by Oscar Montelius to a period and a Bronze Age culture in Scandinavian

Humanity's most fundamental understanding of the Sun is as the luminous disk in the sky, whose presence above the horizon creates day and whose absence causes night. The sky is the part of the Atmosphere or of Outer space visible from the surface of any Astronomical object. The horizon ( Ancient Greek ὁ ὁρίζων, /ho horídzôn/ from ὁρίζειν, "to limit" is the apparent line that separates In many prehistoric and ancient cultures, the Sun was thought to be a solar deity or other supernatural phenomenon. "Sun god" redirects here For the Ramsey Lewis album see Sun Goddess (album. The term supernatural or supranatural ( Latin: super, supra "above" + natura "nature" pertains to entities events Worship of the Sun was central to civilizations such as the Inca of South America and the Aztecs of what is now Mexico. "Sun god" redirects here For the Ramsey Lewis album see Sun Goddess (album. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a Aztec is a term used to refer to certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who achieved political The United Mexican States ( or commonly Mexico (ˈmɛksɪkoʊ () is a federal constitutional Republic in North America. Many ancient monuments were constructed with solar phenomena in mind; for example, stone megaliths accurately mark the summer solstice (some of the most prominent megaliths are located in Nabta Playa, Egypt, and at Stonehenge, England); Newgrange, a prehistoric human-built mount in Ireland, was designed to detect the winter solstice; the pyramid of El Castillo at Chichén Itzá in Mexico is designed to cast shadows in the shape of serpents climbing the pyramid at the vernal and autumn equinoxes. Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes Nabta Playa was once a large Basin in the Nubian Desert, located approximately 500 miles south of modern day Cairo or about 100 kilometers west of This article is about the country of Egypt For a topic outline on this subject see List of basic Egypt topics. Stonehenge is a Prehistoric Monument located in the English county of Wiltshire, about west of Amesbury and north of Salisbury England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Newgrange (Dún Fhearghusa is one of the Passage tombs of the Brú na Bóinne complex in County Meath, one of the most famous Ireland (pronounced /ˈaɾlənd/ Éire) is the third largest island in Europe, and the twentieth-largest island in the world El Castillo ( Spanish for "The Castle " is the nickname of a spectacular Mesoamerican step-pyramid that dominates the center Chichen Itza (tʃiːˈtʃɛn iːˈtsɑː from Chi'ch'èen Ìitsha' "At the mouth of the well of the Itza " is a A pyramid is a Building where the upper surfaces are triangular and converge on one point An equinox is the event of the Sun passing over the Earth's equator in its annual cycle With respect to the fixed stars, the Sun appears from Earth to revolve once a year along the ecliptic through the zodiac, and so Greek astronomers considered it to be one of the seven planets (Greek planetes, "wanderer"), after which the seven days of the week are named in some languages. The fixed stars (from the Latin stellae fixae) are celestial objects that do not seem to move in relation to the other stars of the night sky The ecliptic is the apparent path that the Sun traces out in the sky during the year Zodiac denotes an annual cycle of twelve stations along the Ecliptic, the apparent path of the sun across the heavens through the Constellations that divide the ecliptic A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is A week (also called sennight or sevennight) is a unit of Time longer than a Day and shorter than a Month.

Development of scientific understanding

One of the first people to offer a scientific explanation for the Sun was the Greek philosopher Anaxagoras, who reasoned that it was a giant flaming ball of metal even larger than the Peloponnesus, and not the chariot of Helios. The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca Philosophy is the study of general problems concerning matters such as existence knowledge truth beauty justice validity mind and language Anaxagoras ( Greek: Ἀναξαγόρας c 500 BC &ndash 428 BC was a Pre-Socratic Greek philosopher famous for introducing the Cosmological The Peloponnese or Peloponnesus ( Greek: Πελοπόννησος Pelopónnisos; see also List of Greek place names) is a large Peninsula The chariot is the earliest and simplest type of Carriage, used in both peace and war as the chief vehicle of many ancient peoples In Greek mythology the Sun was personified as Helios (ˈhiliˌɑs ( Ἥλιος Latinized as Helius) For teaching this heresy, he was imprisoned by the authorities and sentenced to death, though he was later released through the intervention of Pericles. Heresy is an introduced change to some system of belief especially a religion that conflicts with the previously established canon of that belief Capital punishment, the death penalty or execution, is the Killing of a person by judicial process as Punishment. Pericles (also spelled Perikles) (c 495 – 429 BC Greek:, meaning "surrounded by glory" was a prominent and influential Statesman, orator Eratosthenes might have been the first person to have accurately calculated the distance from the Earth to the Sun, in the 3rd century BCE, as 149 million kilometers, roughly the same as the modern accepted figure. Eratosthenes of Cyrene ( Greek; 276 BC - 194 BC was a Greek Mathematician, Poet, athlete, Geographer and

The theory that the Sun is the center around which the planets move was apparently proposed by the ancient Greek Aristarchus and Indians (see Heliocentrism). Aristarchus (Ἀρίσταρχος 310 BC - ca 230 BC) was a Greek Astronomer and Mathematician, born on the island of In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System. This view was revived in the 16th century by Nicolaus Copernicus. In the early 17th century, the invention of the telescope permitted detailed observations of sunspots by Thomas Harriot, Galileo Galilei and other astronomers. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. Thomas Harriot ( c 1560 – 2 July 1621) was an English astronomer, Mathematician, Ethnographer, and Translator Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher Galileo made some of the first known Western observations of sunspots and posited that they were on the surface of the Sun rather than small objects passing between the Earth and the Sun. ^[60] Sunspots were also observed since the Han dynasty and Chinese astronomers maintained records of these observations for centuries. The Han Dynasty ( 206 BC–220 AD followed the Qin Dynasty and preceded the Three Kingdoms in China. In 1672 Giovanni Cassini and Jean Richer determined the distance to Mars and were thereby able to calculate the distance to the Sun. Giovanni Domenico Cassini ( June 8, 1625 &ndash September 14, 1712) was an Italian Mathematician, Astronomer Jean Richer (1630 - 1696 was a French Astronomer and assistant ( élève astronome) of Giovanni Domenico Cassini. Isaac Newton observed the Sun's light using a prism, and showed that it was made up of light of many colors,^[61] while in 1800 William Herschel discovered infrared radiation beyond the red part of the solar spectrum. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements In Optics, a prism is a transparent optical element with flat polished surfaces that refract Light. Sir Frederick William Herschel FRS KH ( 15 November 1738 – 25 August 1822) was a German -born British Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of ^[62] The 1800s saw spectroscopic studies of the Sun advance, and Joseph von Fraunhofer made the first observations of absorption lines in the spectrum, the strongest of which are still often referred to as Fraunhofer lines. Joseph von Fraunhofer ( March 6, 1787 &ndash June 7, 1826) was a German optician A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared When expanding the spectrum of light from the Sun, there are large number of missing colors can be found.

In the early years of the modern scientific era, the source of the Sun's energy was a significant puzzle. Lord Kelvin suggested that the Sun was a gradually cooling liquid body that was radiating an internal store of heat. William Thomson 1st Baron Kelvin (or Lord Kelvin) OM, GCVO, PC, PRS, FRSE, (26 June 1824 &ndash 17 December 1907 ^[63] Kelvin and Hermann von Helmholtz then proposed the Kelvin-Helmholtz mechanism to explain the energy output. The Kelvin–Helmholtz mechanism is an astronomical process that occurs when the surface of a Star or a Planet cools Unfortunately the resulting age estimate was only 20 million years, well short of the time span of several billion years suggested by geology. In 1890 Joseph Lockyer, who discovered helium in the solar spectrum, proposed a meteoritic hypothesis for the formation and evolution of the Sun. Sir Joseph Norman Lockyer, FRS ( May 17, 1836 &ndash August 16, 1920) was an English scientist and astronomer ^[64]

Not until 1904 was a substantiated solution offered. Ernest Rutherford suggested that the Sun's output could be maintained by an internal source of heat, and suggested radioactive decay as the source. Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. ^[65] However it would be Albert Einstein who would provide the essential clue to the source of the Sun's energy output with his mass-energy equivalence relation E = mc². Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical In Physics, mass–energy equivalence is the concept that for particles slower than light any Mass has an associated Energy and vice versa.

In 1920 Sir Arthur Eddington proposed that the pressures and temperatures at the core of the Sun could produce a nuclear fusion reaction that merged hydrogen (protons) into helium nuclei, resulting in a production of energy from the net change in mass. Sir Arthur Stanley Eddington, OM (28 December 1882 – 22 November 1944 was an English Astrophysicist of the early 20th century ^[66] The preponderance of hydrogen in the Sun was confirmed in 1925 by Cecilia Payne. Cecilia Payne-Gaposchkin ( May 10 1900 &ndash December 7 1979) was an English - American Astronomer who in 1925 The theoretical concept of fusion was developed in the 1930s by the astrophysicists Subrahmanyan Chandrasekhar and Hans Bethe. Padma Vibhushan Subrahmanyan Chandrasekhar, FRS ( Tamil: சுப்பிரமணியன் சந்திரசேகர் English ˌtʃʌndrəˈʃeɪkɑr( Hans Albrecht Bethe (/hans ˈalbʀɛçt ˈbeːtə/ ( July 2 1906 &ndash March 6, 2005) was a German - American Physicist Hans Bethe calculated the details of the two main energy-producing nuclear reactions that power the Sun. ^[67][68]

Finally, a seminal paper was published in 1957 by Margaret Burbidge, entitled "Synthesis of the Elements in Stars". Margaret Burbidge FRS (born August 12, 1919 in Davenport) is an English Astrophysicist, noted for original research and holding many ^[69] The paper demonstrated convincingly that most of the elements in the universe had been synthesized by nuclear reactions inside stars, some like our Sun. Nucleosynthesis is the process of creating new atomic nuclei from preexisting Nucleons (protons and neutrons This revelation stands today as one of the great achievements of science.

Solar space missions

Solar "fireworks" in sequence as recorded in November 2000 by four instruments onboard the SOHO spacecraft. A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December

The first satellites designed to observe the Sun were NASA's Pioneers 5, 6, 7, 8 and 9, which were launched between 1959 and 1968. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The US Pioneer program of Unmanned space missions was designed for planetary exploration These probes orbited the Sun at a distance similar to that of the Earth, and made the first detailed measurements of the solar wind and the solar magnetic field. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Pioneer 9 operated for a particularly long period of time, transmitting data until 1987. ^[70]

In the 1970s, Helios 1 and the Skylab Apollo Telescope Mount provided scientists with significant new data on solar wind and the solar corona. The Helios deep Space probes were launched in the mid 1970s by the Federal Republic of Germany and NASA, using US Air Force launch vehicles Skylab was the first Space station the United States launched into orbit and the second space station ever visited by a human crew The Helios 1 satellite was a joint U.S.-German probe that studied the solar wind from an orbit carrying the spacecraft inside Mercury's orbit at perihelion. The United States of America —commonly referred to as the Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from The Skylab space station, launched by NASA in 1973, included a solar observatory module called the Apollo Telescope Mount that was operated by astronauts resident on the station. An observatory is a location used for observing terrestrial and/or celestial events Skylab made the first time-resolved observations of the solar transition region and of ultraviolet emissions from the solar corona. Discoveries included the first observations of coronal mass ejections, then called "coronal transients", and of coronal holes, now known to be intimately associated with the solar wind. A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. Coronal holes are areas where the Sun's Corona is darker colder and has lower-density plasma than average The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun.

In 1980, the Solar Maximum Mission was launched by NASA. The Solar Maximum Mission Satellite (or SolarMax was designed to investigate solar phenomenon particularly Solar flares. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program This spacecraft was designed to observe gamma rays, X-rays and UV radiation from solar flares during a time of high solar activity. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares Just a few months after launch, however, an electronics failure caused the probe to go into standby mode, and it spent the next three years in this inactive state. In 1984 Space Shuttle Challenger mission STS-41C retrieved the satellite and repaired its electronics before re-releasing it into orbit. Space Shuttle Challenger ( NASA Orbiter Vehicle Designation: OV-099 was NASA's second Space Shuttle orbiter to be put into service The Solar Maximum Mission subsequently acquired thousands of images of the solar corona before re-entering the Earth's atmosphere in June 1989. ^[71]

Japan's Yohkoh (Sunbeam) satellite, launched in 1991, observed solar flares at X-ray wavelengths. For a topic outline on this subject see List of basic Japan topics. Yohkoh ( Sunbeam in Japanese) also known as Solar-A, was a Japanese Institute of Space and Astronautical Science Solar mission Mission data allowed scientists to identify several different types of flares, and also demonstrated that the corona away from regions of peak activity was much more dynamic and active than had previously been supposed. Yohkoh observed an entire solar cycle but went into standby mode when an annular eclipse in 2001 caused it to lose its lock on the Sun. A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured It was destroyed by atmospheric reentry in 2005. ^[72]

One of the most important solar missions to date has been the Solar and Heliospheric Observatory, jointly built by the European Space Agency and NASA and launched on December 2, 1995. The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Events 1409 - The University of Leipzig opens 1755 - The second Eddystone Lighthouse is destroyed by fire Year 1995 ( MCMXCV) was a Common year starting on Sunday. Events of 1995 Originally a two-year mission, SOHO has now operated for over ten years (as of 2007). It has proved so useful that a follow-on mission, the Solar Dynamics Observatory, is planned for launch in 2008. The Solar Dynamics Observatory (SDO is a NASA mission under the Living With a Star (LWS program Situated at the Lagrangian point between the Earth and the Sun (at which the gravitational pull from both is equal), SOHO has provided a constant view of the Sun at many wavelengths since its launch. In addition to its direct solar observation, SOHO has enabled the discovery of large numbers of comets, mostly very tiny sungrazing comets which incinerate as they pass the Sun. A sungrazing comet is a Comet that passes extremely close to the Sun at Perihelion - sometimes within a few thousand kilometres of the Sun's surface ^[73]

The Sun's south pole, taken by STEREO solar observation mission. STEREO (Solar TErrestrial RElations Observatory is a solar observation mission which was launched on 26 October 2006 at 0052 GMT. Material can be seen erupting off the Sun in the lower right side of the image.

All these satellites have observed the Sun from the plane of the ecliptic, and so have only observed its equatorial regions in detail. The Ulysses probe was launched in 1990 to study the Sun's polar regions. Ulysses is a robotic Space probe designed to study the Sun at all latitudes It first traveled to Jupiter, to 'slingshot' past the planet into an orbit which would take it far above the plane of the ecliptic. Serendipitously, it was well-placed to observe the collision of Comet Shoemaker-Levy 9 with Jupiter in 1994. Shoemaker-Levy redirects here For other Shoemaker-Levy comets see List of periodic comets. Once Ulysses was in its scheduled orbit, it began observing the solar wind and magnetic field strength at high solar latitudes, finding that the solar wind from high latitudes was moving at about 750 km/s which was slower than expected, and that there were large magnetic waves emerging from high latitudes which scattered galactic cosmic rays. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on ^[74]

Elemental abundances in the photosphere are well known from spectroscopic studies, but the composition of the interior of the Sun is more poorly understood. Astronomical spectroscopy is the technique of Spectroscopy used in Astronomy. A solar wind sample return mission, Genesis, was designed to allow astronomers to directly measure the composition of solar material. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. The Genesis spacecraft was the first ever attempt to collect a sample of Solar wind, and the first " Sample return mission " to return from beyond the Genesis returned to Earth in 2004 but was damaged by a crash landing after its parachute failed to deploy on reentry into Earth's atmosphere. A parachute is a device used to slow the motion of an object through an atmosphere by creating drag. Despite severe damage, some usable samples have been recovered from the spacecraft's sample return module and are undergoing analysis.

The Solar Terrestrial Relations Observatory (STEREO) mission was launched in October 2006. STEREO (Solar TErrestrial RElations Observatory is a solar observation mission which was launched on 26 October 2006 at 0052 GMT. Two identical spacecraft were launched into orbits that cause them to (respectively) pull further ahead of and fall gradually behind the Earth. This enables stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections. Stereoscopy, stereoscopic imaging or 3-D (three-dimensional imaging is any technique capable of recording three-dimensional visual A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph.

If one were to observe it from Alpha Centauri, the closest star system, the Sun would appear to be in the constellation Cassiopeia. Alpha Centauri (α Centauri / α Cen also known as Rigil Kentaurus, Rigil Kent, or Toliman, is the brightest Star in the southern Constellation Cassiopeia ( colloquially /ˌkæsiˈoʊpiə/ is a northern Constellation which Greek mythology considered to represent the vain queen Cassiopeia who boasted

Observation and eye damage

The Sun as it appears through a camera lens from the surface of Earth

Sunlight is very bright, and looking directly at the Sun with the naked eye for brief periods can be painful, but is not particularly hazardous for normal, non-dilated eyes. A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with The naked eye is a Figure of speech referring to human Visual perception that is unaided by enhancing equipment such as a Telescope or ^[75][76] Looking directly at the Sun causes phosphene visual artifacts and temporary partial blindness. "Phosphene" is also a common alternative spelling of Phosphine, PH3 a toxic and explosive gas It also delivers about 4 milliwatts of sunlight to the retina, slightly heating it and potentially causing damage in eyes that cannot respond properly to the brightness. ^[77][78] UV exposure gradually yellows the lens of the eye over a period of years and is thought to contribute to the formation of cataracts, but this depends on general exposure to solar UV, not on whether one looks directly at the Sun. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays A cataract is a clouding that develops in the crystalline lens of the Eye or in its envelope varying in degree from slight to complete opacity ^[79] Long-duration viewing of the direct Sun with the naked eye can begin to cause UV-induced, sunburn-like lesions on the retina after about 100 seconds, particularly under conditions where the UV light from the Sun is intense and well focused;^[80][81] conditions are worsened by young eyes or new lens implants (which admit more UV than aging natural eyes), Sun angles near the zenith, and observing locations at high altitude.

Viewing the Sun through light-concentrating optics such as binoculars is very hazardous without an appropriate filter that blocks UV and substantially dims the sunlight. Binocular telescopes, or binoculars (also known as field glasses are two identical or Mirror - symmetrical telescopes mounted side-by-side and An attenuating (ND) filter might not filter UV and so is still dangerous. In Photography and Optics, a neutral density filter or ND filter is a "grey" filter Unfiltered binoculars can deliver over 500 times as much energy to the retina as using the naked eye, killing retinal cells almost instantly (even though the power per unit area of image on the retina is the same, the heat cannot dissipate fast enough because the image is larger). Even brief glances at the midday Sun through unfiltered binoculars can cause permanent blindness. ^[82] One way to view the Sun safely is by projecting its image onto a screen using a telescope and eyepiece without cemented elements. This should only be done with a small refracting telescope (or binoculars) with a clean eyepiece. Other kinds of telescopes can be damaged by this procedure.

Partial solar eclipses are hazardous to view because the eye's pupil is not adapted to the unusually high visual contrast: the pupil dilates according to the total amount of light in the field of view, not by the brightest object in the field. A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured The pupil is the hole that is located in the center of the iris of the eye and that controls the amount of light that enters the Eye. During partial eclipses most sunlight is blocked by the Moon passing in front of the Sun, but the uncovered parts of the photosphere have the same surface brightness as during a normal day. Surface brightness is a concept used in Astronomy when describing extended Astronomical objects such as galaxies and Nebulae General In the overall gloom, the pupil expands from ~2 mm to ~6 mm, and each retinal cell exposed to the solar image receives about ten times more light than it would looking at the non-eclipsed Sun. This can damage or kill those cells, resulting in small permanent blind spots for the viewer. ^[83] The hazard is insidious for inexperienced observers and for children, because there is no perception of pain: it is not immediately obvious that one's vision is being destroyed.

During sunrise and sunset, sunlight is attenuated due to Rayleigh scattering and Mie scattering from a particularly long passage through Earth's atmosphere and the direct Sun is sometimes faint enough to be viewed comfortably with the naked eye or safely with optics (provided there is no risk of bright sunlight suddenly appearing through a break between clouds). Sunrise is the instant at which the upper edge of the Sun appears above the Horizon in the East. Sunset, also called sundown in some American English Dialects is the instant when the trailing edge of the Sun 's disk disappears below Rayleigh scattering (named after Lord Rayleigh) is the elastic Scattering of Light or other electromagnetic radiation by particles much smaller Mie theory, also called Lorenz-Mie theory or Lorenz-Mie-Debye theory, is a complete analytical solution of Maxwell's equations for the Scattering Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation.

Attenuating filters to view the Sun should be specifically designed for that use: some improvised filters pass UV or IR rays that can harm the eye at high brightness levels. Filters on telescopes or binoculars should be on the objective lens or aperture, never on the eyepiece, because eyepiece filters can suddenly crack or shatter due to high heat loads from the absorbed sunlight. An objective in Optics is the lens or Mirror in a Microscope, Telescope, camera or other optical instrument For the device for looking through a camera see Viewfinder. An eyepiece, or ocular lens, is a type of lens that is attached Welding glass #14 is an acceptable solar filter, but "black" exposed photographic film is not (it passes too much infrared).

In cultural history

Like other natural phenomena, the Sun has been an object of veneration in many cultures throughout human history. Sol (pronounced /sɒl/ in English) is the Latin word for "Sun". Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. The Latin name is widely known, but not common in general English language use, although the adjectival form is the related word solar. 'Sol' is more often used in science fiction writing (Star Trek in particular) as a formal name for the specific star, since in many stories the local Sun is a different star and thus the generic term "the Sun" would be ambiguous. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth By extension, the Solar System is often referred to in science fiction as the "Sol System". The Solar System consists of the Sun and those celestial objects bound to it by Gravity. 'Sol' is sometimes used in scientific circles, but 'Sol' is not the "official" name of the Sun, and the word 'Sol' makes no appearances in common reference sources. ^[84]

The term sol is used by planetary astronomers to refer to the duration of a solar day on Mars. Solar times are measures of the apparent position of the Sun on the Celestial sphere. ^[85] A mean Earth solar day is approximately 24 hours, while a mean Martian sol, is 24 hours, 39 minutes, and 35. 244 seconds. ^[86] See also Timekeeping on Mars. Various schemes have been used or proposed to keep track of time and date on the planet Mars independently of Earth time and calendars

Sol is also the modern word for "Sun" in Portuguese, Spanish, Icelandic, Danish, Norwegian, Swedish, Catalan and Galician. Portuguese ( or língua portuguesa) is a Romance language that originated in what is now Galicia (Spain and northern Portugal. Icelandic ( is a North Germanic language, the language of Iceland. Danish ( d̥ænsɡ̊ is one of the North Germanic languages (also called Scandinavian languages a sub-group of the Germanic branch of the Norwegian ( norsk) is a North Germanic Language spoken primarily in Norway, where it is an official language Swedish ( is a North Germanic language spoken by more than nine million people predominantly in Sweden and parts of Finland, especially along the Catalan ˈkætəˌlæn ( català kətəˈla or) is a Romance language, the national and official language of Andorra, and a co-official The Peruvian currency nuevo sol is named after the Sun (in Spanish), like its successor (and predecessor, in use 1985–1991) the Inti (in Quechua). Peru (Perú Piruw Piruw officially the Republic of Peru ( reˈpuβlika del peˈɾu is a country in western South America. A currency is a unit of exchange, facilitating the transfer of Goods and/or services It is one form of Money, where money is The inti was the Currency of Peru between 1985 and 1991 Its ISO 4217 code was PEI and its abbreviation in local use was "I/ Quechua ( Runa Simi) is a Native American language of South America. In Persian, sol means "solar year". A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons as seen from Earth

In East Asia the Sun is represented by the symbol 日 (Chinese pinyin rì) or 太阳 (tài yáng). Pinyin, more formally Hanyu pinyin, is the most common Standard Mandarin Romanization system in use In Vietnamese these Han words are called nhật and thái dương respectively, while the native Vietnamese word mặt trời literally means 'face of the heavens'. Vietnamese ( tiếng Việt, or less commonly Việt ngữ) formerly known under French colonization as Annamese ( see Annam) The Moon and the Sun are associated with the yin and yang where the Moon represents yin and the Sun yang as dynamic opposites. In Chinese philosophy, the concept of yin and yang ( is used to describe how seemingly opposing forces are bound together intertwined and interdependent in the

See also

References

External links

• Nasa SOHO (Solar & Heliospheric Observatory) satellite
• National Solar Observatory
• Astronomy Cast: The Sun