Movement and location [ change | change source ]

The sun is located near the inner edge of the Orion Arm of the Milky Way , within the Local Interstellar Cloud or the Gould Belt , at a distance of 7.5-8.5 kpc (25,000-28,000 light - years ) from the Galactic Center . ^{[96] [97] [98] [99] [100] [101] The} sun is included in the Local Bula , a space of dilute hot gas, probably created by the remnant of the Geminga supernova, ^[102] or the multiple supernovae in subgroup B1 of the group. Pleiades. ^{[103] The} distance between the local arm and the next arm, the Perseus Arm, is about 6,500 light-years. ^{[104] The} Sun, and therefore the Solar System, is found in what scientists call a galactic habitable zone.

The solar apex is the direction in which the Sun moves relative to other nearby stars. This movement is towards a point in the constellation Hercules , near the star Vega .

At a distance of 32.6 light-years from the Sun there are 315 known stars in 227 systems, including 163 single stars. It is estimated that another 130 systems in this range have not yet been identified. In a distance of up to 81.5 light-years there can be up to 7,500 stars, of which about 2,600 are known. The number of subterranean objects in that volume is expected to be comparable to the number of stars. ^[105] Of the 50 closest star systems within a 17-light-year range of Earth (the closest being the Proxima Centauri red dwarf at about 4.2 light-years), the Sun ranks fourth in the afternoon. to. ^[106]

Orbit the Milky Way [ change | change source ]

The sun orbits the center of the Milky Way and is currently moving in the direction of the constellation Swan . A simple model of the motion of a star in a galaxy has the galactic coordinates X , Y and Z as:

{displaystyle X(t)=X(0)+{frac {U(0)}{kappa }}sin(kappa t)+{frac {V(0)}{2B}}(1-cos(kappa t))}

{displaystyle Y(t)=Y(0)+2Aleft(X(0)+{frac {V(0)}{2B}}right)t-{frac {Omega _{0}}{Bkappa }}V(0)sin(kappa t)+{frac {2Omega _{0}}{kappa ^{2}}}U(0)(1-cos(kappa t))}

{ displaystyle Z (t) = { frac {W (0)} { nu}} sin ( nu t) + Z (0) cos ( nu t)}

where U , V and W are the respective velocities in relation to the local resting standard, A and B are Oort constants,{displaystyle Omega _{0}=A-B} is the angular velocity of the galactic rotation for the local resting standard, {displaystyle kappa ={sqrt {-4Omega _{0}B}}}is the "epicyclic frequency" and ν is the vertical oscillation frequency. ^[107] For the Sun, the current values ​​of U , V and W are estimated as{displaystyle (U(0),V(0),W(0))=(10.00,5.25,7.17)}km / s, and the estimates for the other constants A  = 15.5 km / s / kpc, B  = −12.2 km / s / kpc, κ = 37 km / s / kpc, and ν = 74 km / s / kpc . We take X (0) and Y (0) as zero and Z (0) estimated to be 17 parsecs. ^[108] This pattern implies that the Sun revolves around a point that revolves around the galaxy. The period of the Sun's circulation around the point is{displaystyle 2pi /kappa }, which, using the equivalent of a parsec equal to 1 km / s of 0.978 million years, reaches 166 million years, shorter than the time required to go around the galaxy. In the ( X, Y ) coordinates the sun describes an ellipse around the point, whose length in the Y direction is

{displaystyle 2times {sqrt {left({frac {2Omega _{0}}{kappa ^{2}}}U(0)right)^{2}+left({frac {Omega _{0}}{Bkappa }}V(0)right)^{2}}}=1035{text{ parsec}}.}

and whose width in the X direction is

{displaystyle 2times {sqrt {left({frac {U(0)}{kappa }}right)^{2}+left({frac {V(0)}{2B}}right)^{2}}}=691{text{ parsec}}}

The ratio of the length to the width of this ellipse, the same for all the stars in our neighborhood, is {displaystyle 2Omega /kappa approx 1,50.} The moving point is currently at

{displaystyle X={frac {V(0)}{2B}}=-215{text{ parsec}}}

{displaystyle Y={frac {2Omega _{0}}{kappa ^{2}}}U(0)=405{text{ parsec}}.}

The oscillation in the Z direction takes the Sun.

{displaystyle {sqrt {left({frac {W(0)}{nu }}right)^{2}+Z(0)^{2}}}=98{text{ parsec}}}

above the galactic plane and the same distance below it, with a period of { displaystyle 2 pi / nu}or 83 million years, about 2.7 times in orbit. ^[109] Although{ displaystyle 2 pi / Omega _ {0}} is 222 million years old, its value { displaystyle Omega} at the point where the Sun is moving is

{displaystyle Omega approx Omega _{0}-{frac {2A}{R_{0}}}Delta Xapprox 26.1{text{ km/s/kpc}}}

which corresponds to 235 million years and this is the time required to orbit the galaxy once. Other stars of the same value a{displaystyle X+V/(2B)} they need the same amount of time to bypass the galaxy as the Sun and thus remain in the same general neighborhood as the Sun.

The Sun's orbit around the Milky Way is probably approximately elliptical, with the addition of perturbations in the spiral arms of the galaxy and the uneven mass distribution in the Milky Way. It has been argued that the Sun's passage through higher-density spiral arms often coincides with mass extinctions on Earth, probably due to increased impact events. ^[110]

The complete tour of the Galactic Center (the galactic year) lasts about 225-250 million years, ^[111] so it is believed that so far the Sun has completed 20-25 orbits. The orbital speed of the Solar System around the center of the Milky Way is about 251 km / s. ^[112] At this speed, the Solar System takes about 1,190 years to travel 1 light-year or 7 days to travel 1 AU .

The Milky Way moves in relation to the cosmic background radiation (CMB) in the direction of the constellation Hydra with a speed of 550 km / s, and the resulting speed of the Sun in relation to CMB is about 370 km / s in the direction of the Cup or Leo . ^[113]

Movement in the Solar System [ change | change source ]

The Sun's motion toward the center of mass of the Solar System is very complex due to planetary perturbations. When Jupiter and Saturn (the two planets with the largest mass) are on the same side of the Sun, the center of gravity of the Solar System is beyond the surface of the Sun; when they are on opposite sides of the star and other planets are in their orbits, the center of gravity can be very close to the center of the Sun. ^[114] Every 179 years (nine times the synodic period of Jupiter and Saturn), the pattern repeats more or less, but rotates about 24 °. ^[115]

Theoretical [ change | change source ]

Heating crown [ change | change source ]

The visible surface of the Sun (photosphere) has a temperature of about 6,000 K, while the temperature of the corona reaches 1,000,000-2,000,000 K. ^[54] The high temperature of the corona shows that it is heated by something other than the direct conduction of heat from photosphere. ^[56]

It is believed that the energy needed to heat the corona is provided by the turbulent motion in the convection zone under the photosphere and two main mechanisms have been proposed to explain coronal heating. ^{[54] The} first is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone. ^[54] These waves move and dissipate in the corona, releasing energy into the gas in the form of heat. ^[116] The second mechanism is heating by a magnetic field: magnetic energy is continuously accumulated by the movement of the photosphere and released by magnetic reconnection in the form of large sunbeams and a lot of similar but smaller events. ^[117]

At present, it is not clear whether the waves are an efficient heating mechanism. All the waves, except the Alfvén waves, proved to dissipate or refract before reaching the crown. ^[118] In addition, Alfvén waves do not dissipate easily in the corona. Therefore, current research has focused on sudden-intensity combustion heating mechanisms. ^[54]

The problem of weak early sun [ change | change source ]

Theoretical models of the Sun's development suggest that 3.8 to 2.5 billion years ago, during the Archaic eon , the Sun had a brightness of only about 75% of that of today. Such a faint star would not have been able to support liquid water on the Earth's surface, and thus life would not have had to develop. However, the geological record shows that the Earth has remained at a fairly constant temperature throughout its history and that the young Earth has been somewhat warmer than it is today. One theory among scientists is that the young Earth's atmosphere contained much larger amounts of greenhouse gases (such as carbon dioxide , methane).) than today, which caught enough heat to compensate for the smaller amount of solar energy reaching the planet. ^[119]

However, the examination of sediments from the Archaic seems incompatible with the hypothesis of high greenhouse concentrations. Instead, the moderate temperature range can be explained by a lower surface albedo . This would have led to an increased absorption of solar energy, thus compensating for the reduced power of solar energy. ^[120]

History observations [ change | change source ]

The enormous effect of the Sun on Earth has been recognized since prehistoric times, and the Sun has been considered a deity in some cultures.

In antiquity [ change | change source ]

The sun has been an object of veneration in many cultures throughout human history. In the most basic understanding, the Sun is a luminous disk in the sky, whose presence above the horizon creates day and whose absence causes night. In many prehistoric and ancient cultures, the Sun was considered a god or a supernatural phenomenon. The worship of the Sun was the center of the religious life of many civilizations, such as ancient Egypt , the Inca Empire of South America and the Aztecs of what is now Mexico. In some religions, such as Hinduism , the Sun is still considered a god. ^[121] In prehistory, humans created numerous monuments to observe phenomena related to the Sun; for example, megalithswere used to mark precisely the solstices of summer and winter (such megaliths found in Nabta Playa, Egypt, Mnajdra, Malta and Stonehenge , England); Newgrange, a mountain built by prehistoric people in Ireland, was designed to accurately identify the day of the winter solstice; El Castillo's pyramid at Chichén Itzá in Mexico was built so that, during the spring and autumn equinoxes, the shadows on the walls of the pyramid would take the form of creepy snakes. ^[122]

The ancient Egyptians depicted the god Ra as being driven through the sky in a solar boat, accompanied by smaller gods, ^[123] and to the Greeks, the god Helios , the personification of the Sun, was carried by a chariot drawn by fire horses. ^[124] During the reign of the Roman emperor Elagabalus , the birthday of the Sun was celebrated as Sol Invictus (literally "Invincible Sun"), shortly after the winter solstice, which could have been a precedent for Christmas. ^[125] Each year, the Sun seemed to move against the background of fixed stars along the ecliptic, through the signs of the zodiac; for this reason, Greek astronomers have recognized that this is one of the sevenplanets (Greek πλανήτες, planetes , means "wanderer"); the name of the days of the weeks after the seven planets dates back to Roman times . ^{[126] [127] [128]}

Developing scientific understanding [ change | change source ]

At the beginning of the first millennium BC, Babylonian astronomers observed that the motion of the Sun along the ecliptic is not uniform, although they did not know why; today it is known that this is due to the motion of the Earth in an elliptical orbit around the Sun, the Earth moving faster when it is closer to the Sun at perihelion and slower when it is farther away at aphelion. ^[129]

One of the first people to give a scientific or philosophical explanation for the Sun was the Greek philosopher Anaxagoras . He considered it a giant ball of burning metal, even larger than the land of the Peloponnese, and that the Moon reflected the light of the Sun. ^[130] As this was clearly contrary to the religious description of the Sun as the chariot of the god Helios, he was imprisoned for preaching heresy and sentenced to exile ^[131] or death, although he was later released due to Pericles ' intervention . Eratosthenes estimated the distance between the Earth and the Sun in the third century BC. as “400 and 80,000 stages”, the translation of which is ambiguous, involving either 4,080,000stages (755,000 km), or 804,000,000 stages (148 to 153 million kilometers); the last value being approximately correct. In the first century AD, Ptolemy estimated the distance to be 1,210 times the radius of the Earth, about 7.71 million kilometers. ^[132]

The theory that the sun is the center around which the planets orbit was first proposed by the Greek Aristarchus of Samos in the third century BC, and later adopted by Seleucus of Seleucia (see Heliocentrism ). This vision was developed in a more detailed mathematical model of a 16th century heliocentric system by Nicolaus Copernicus .

Observations of sunspots were recorded during the Han Dynasty (206 BC - 220 AD) by Chinese astronomers, who kept records of these observations for centuries. Averroes also provided a description of sunspots in the 12th century. ^{[133] The} invention of the telescope in the early seventeenth century allowed detailed observation of sunspots by Thomas Harriot , Galileo Galilei and other astronomers. Galileo hypothesized that sunspots were on the surface of the Sun and were not small objects passing between the Earth and the Sun. ^[134]

In the Middle Ages , astronomy developed in Muslim countries. Al-Battani discovered that the direction of the Sun's peak was changing. ^[135] (In modern heliocentric terms, this is caused by a gradual movement of the aphelion of the Earth's orbit). Ibn Yunus observed more than 10,000 measurements for the position of the Sun for many years using a large astrolabe . ^[136]

From an observation of the transit of Venus in 1032, the Persian astronomer and polymath Ibn Sina (Avicenna) came to the conclusion that Venus is closer to Earth than to the Sun. ^[137] In 1672, Giovanni Cassini and Jean Richer determined the distance from Mars and were able to calculate the distance to the Sun.

In 1666, Isaac Newton observed sunlight using a prism and showed that it is made up of several colors. ^[138] In 1800, William Herschel discovered infrared radiation outside the red part of the sunlight spectrum. ^[139]

In the nineteenth century, great advances were made in spectroscopic studies of the Sun; Joseph von Fraunhofer recorded over 600 absorption lines in the solar spectrum; the strongest are still called Fraunhofer lines. In the early years of the modern scientific era, the Sun's energy source was a great mystery. Lord Kelvin suggested that the Sun is a liquid body that cools gradually, radiating internal heat. ^[140] Kelvin and Hermann von Helmholtzproposed a gravitational contracting mechanism to explain energy production, but the resulting estimated age of the Sun was only 20 million years, too short for at least 300 million years suggested by some geological discoveries of those times. ^[140] [141] In 1890, Joseph Lockyer , who discovered helium in the solar spectrum, proposed a meteoritic hypothesis for the formation and evolution of the Sun. ^[142]

It was not until 1904 that a documented solution was offered. Ernest Rutherford suggested that the power of solar radiation can be sustained by internal heat sources and suggested radioactive degradation as a source. ^[143] An essential indication of the source of solar energy was provided by the work of Albert Einstein , who showed the equivalence of mass and energy in the relation E = mc ² . ^[144] In 1920, Sir Arthur Eddingtonhypothesized that pressures and temperatures in the Sun's nucleus could produce a nuclear fusion reaction that connects hydrogen protons to helium nuclei, leading to the release of energy associated with a mass deficit of the helium nucleus. ^{[145] The} preponderance of hydrogen in the Sun was confirmed in 1925 by Cecilia Payne using the ionization theory developed by Meghnad Saha . The theoretical concept of fusion was developed in the 1930s by astrophysicists Subrahmanyan Chandrasekhar and Hans Bethe . Hans Bethe calculated the details of the two energy-producing nuclear reactions that power the Sun. ^[146] [147]In 1957, a collective work entitled "Synthesis of Elements in Stars" was published (authors: Margaret Burbidge , Geoffrey Burbidge , William Fowler, and Fred Hoyle ), which convincingly demonstrated that most elements in the universe were formed in star fusion processes. , some like the Sun. ^[148]

Solar space missions [ change | change source ]

The first satellites to observe the Sun were the American Pioneer probes : Pioneer 6, 7, 8 and 9, which were launched between 1959 and 1968. These probes orbited the Sun from a distance similar to that of Earth and made the first detailed measurements of the solar wind and the solar magnetic field. Pioneer 9 operated for a particularly long time, transmitting data until May 1983. ^[149] [150] In the 1970s, two Helios spacecraft and Skylab's Apollo Telescope Mount provided scientists with significant new data about the solar wind.and the solar corona. The Helios 1 and 2 probes, which were the result of American-German cooperation, studied the solar wind in the orbit whose periheion was in Mercury 's orbit . ^[151] The Skylab space station, launched by NASA in 1973, included a solar observation module called the Apollo Telescope Mount, which was operated by astronauts living in the station. ^[55] Skylab provided information on the transition layer of the solar atmosphere and recorded ultraviolet emissions from the solar corona. ^[55] Among the findings were the first observations of coronal mass ejections and coronal holes, which are now known to be closely related to the solar wind. ^[151]

In 1980, NASA launched the Solar Maximum mission. This satellite was designed to observe gamma rays, X-rays and UV rays in solar flares during high solar activity. Just a few months after the start of the mission, an electronics error caused the satellite to enter standby mode and did not work for the next three years. In 1984, the Challenger shuttle intercepted the satellite and repaired it, after which the satellite returned to Earth orbit. Solar Maximum Mission completed approximately 240,000 photographs of the corona before entering Earth's atmosphere in June 1989. ^[152]

Launched in 1991, the Japanese satellite Yohkoh ("Sunbeam") observed solar flares at X-ray wavelengths. than previously thought. Yohkoh observed an entire solar cycle, but went into standby mode when a 2001 ring eclipse caused him to lose control of the Sun's position. The satellite was destroyed by re-entry into the atmosphere in 2005. ^[153]

One of the most important solar missions to date has been the Solar and Heliosphere Observatory , built jointly by the European Space Agency and NASA and launched on 2 December 1995. ^[55] Originally planned to carry out a two-year mission, it has been expanded. until 2012 ^[154] and then until 2016. The probe was placed in the Lagrange Point L1 between Earth and the Sun and constantly monitored the Sun at several wavelengths. ^[55] In addition to direct observation of the Sun, it also led to the discovery of a large number of comets , mainly small comets that were destroyed as they passed the Sun.^{[155] The} SOHO Observatory proved to be so useful that in February 2010 the Solar Dynamics Observatory (SDO) was sent to continue the mission. ^[156]

All these probes observed the Sun from the ecliptic plane, which allows detailed observations only in the equatorial region. The Ulysses spacecraft was launched in 1990 to study the polar regions of the Sun. He first traveled to Jupiter, so that the planet's gravitational assistance would allow it to exit far above the plane of the ecliptic. Unexpectedly, the probe was at the right place and time to observe the collision of Comet Shoemaker-Levy 9 with Jupiter in 1994. When Ulysseswas in planned orbit, began to observe the solar wind and the force of the magnetic field at high heliographic latitudes, discovering that high-latitude solar wind travels at about 750 km / s, slower than expected and that large magnetic waves emitted from heliographic latitudes large scattering galactic cosmic rays. ^[157]

The content of elements in the photosphere is well known due to spectroscopic studies, but the composition inside the Sun is much less known. A return mission with solar wind samples, Genesis , was designed to allow astronomers to directly measure the composition of solar material. ^[158] Genesis returned to Earth in 2004, but the probe's parachute did not open during the flight through the atmosphere and the lander collapsed. Despite the serious damage, some samples were recovered from the broken capsule and are being analyzed. ^[159]

The STEREO (Solar Terrestrial Relations Observatory) mission was launched in October 2006. Two identical space probes were launched into orbit, with one probe in front of Earth and the other following it behind Earth. This allows stereoscopic images of the Sun and solar phenomena, such as coronal mass ejections. ^[160] [161]

The Parker spacecraft was launched in 2018 and is to make observations inside the solar corona to explain the mechanisms of corona heating and the acceleration of the solar wind. It will approach the Sun at a minimum distance of 2.3 million kilometers in 2025. ^[162] In February 2020, ESA in cooperation with NASA launched the Solar Orbiter probe to investigate how the Sun creates and controls the behavior of the heliosphere. The mission is planned to last 7 years. Indian space research organization has scheduled the launch of a 100 kg satellite called Aditya-L1by the end of 2020. The main tool will be a coronagraph to study the dynamics of the solar corona. ^[163]

Observations and effects [ change | change source ]

Sunlight can cause pain when you look at it with the naked eye; if done for a short time and with the eyes half closed, it is not dangerous for normal eyes. ^[164] [165] Direct gaze of the Sun causes temporary partial blindness. During this action, about 4 milliwats of light hit the retina, warming it slightly, which can cause eye damage. ^[166] [167] Exposure to ultraviolet light causes a gradual yellowing of the lens of the eyes over the years and contributes to the formation of cataracts , but this depends on the general exposure to UV solar radiation and not if we look directly at the Sun. ^[168]Prolonged viewing of the Sun directly with the naked eye can cause damage caused by solar radiation to the retina after about 100 seconds, especially when the UV light from the Sun is intense and well focused. ^[169] [170] The effects are stronger if the sun is near its zenith or observed at high altitudes; also, young eyes and lens implants (especially from older generations) do not filter ultraviolet light as effectively as naturally aging eyes.

Visualizing the Sun with light-focusing optical instruments, such as binoculars without a proper filter that blocks UV radiation and significantly darkens sunlight, can lead to permanent damage to the retina. ^[171] For observation, use specially designed filters. Some makeshift filters that allow ultraviolet or infrared rays to pass through can damage the eye at high brightness levels. ^[172] Binoculars without filters can provide energy hundreds of times more than when you look directly at the Sun, and can cause immediate damage. Even a brief glance at the sun at noon through an unfiltered telescope can cause permanent eye damage. ^[173]

Partial solar eclipses are dangerous for observers because the pupil of the eye is not adapted to the unusually high visual contrast: the pupil dilates or narrows depending on the total amount of light in the field of view, not the brightness of the brightest object. During partial eclipses, most of the sunlight is blocked by the Moon passing in front of the Sun, but the exposed parts of the photosphere have the same brightness as during a normal day. When the total amount of light is reduced, the pupil expands from ~ 2 mm to ~ 6 mm, and each retinal cell exposed to sunlight receives up to ten times more light than when looking at the Sun that is not eclipsed. ^[174] The danger is insidious for inexperienced observers and children, because there is no perception of pain: it is not immediately obvious that someone's sight is destroyed.

During sunrise and sunset, sunlight is dimmed and the Sun is sometimes dim enough to be seen comfortably with the naked eye or safely with the use of optical instruments (provided there is no risk of sudden brightness, for example, through a break between clouds). ^[175] Fog, dust and high humidity contribute to light attenuation. ^[176]

Shortly after sunset or before sunrise, a rare optical phenomenon , known as the green ray , may occur . The flash is caused by sunlight coming just below the horizon, being curved (usually by reversing the temperature) to the observer. Light of shorter wavelengths (purple, blue, green) is more curved than that of longer wavelengths (yellow, orange, red), but light in purple and blue is more diffuse, leaving light that is perceived as green. ^[177]

Ultraviolet light from the Sun has antiseptic properties and can be used to sanitize tools and water. It also causes sunburn and has other biological effects, such as vitamin D production and sun tanning . It is the leading cause of skin cancer . Ultraviolet light is strongly attenuated by the ozone layer of the Earth's atmosphere, so the amount of UV varies greatly with latitude and has been partly responsible for many biological adaptations, including variations in human skin color in different regions of the Earth. ^[178]

Notes [ edit | change source ]

References [ change | change source ]

External links [ change | change source ]

You can find more information about Sun by searching in similar Wikipedia projects, grouped under the generic name "sister projects" :
	Definitions and translations in Wiktionary
	Images and media at Commons
	Quotes from Wikiquote
	Source text at Wikisource
	Manual to Wikimanuale
	Wikiversity study resources

• Nasa SOHO (Solar and Heliospheric Observatory) satellite
• National Solar Observatory
• Astronomy Cast: The Sun
• A collection of spectacular images of the Sun from various institutions (The Boston Globe)
• Satellite observations of solar luminosity
• Sun|Trek, an educational website about the Sun
• The Swedish 1-meter Solar Telescope, SST
• An animated explanation of the structure of the Sun (Universitatea din Glamorgan)
• Animation – The Future of the Sun
• Solar Conveyor Belt Speeds Up – NASA – imagini
• NASA 5-year timelapse video of the Sun
• Sun in Ultra High Definition NASA January 11, 2015

See also [ edit ] change source ]

 

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