149-486: The Global Oscillation Network Group (GONG) is a worldwide network of six identical telescopes, designed to have 24/7 observations of the Sun . The network serves multiple purposes, including the provision of operation data for use in space weather prediction, and the study of solar internal structure and dynamics using helioseismology . Deployed in 1995, GONG is a set of six observing systems geographically distributed around
298-564: A distance of one astronomical unit (AU) from the Sun (that is, at or near Earth's orbit). Sunlight on the surface of Earth is attenuated by Earth's atmosphere , so that less power arrives at the surface (closer to 1,000 W/m ) in clear conditions when the Sun is near the zenith . Sunlight at the top of Earth's atmosphere is composed (by total energy) of about 50% infrared light, 40% visible light, and 10% ultraviolet light. The atmosphere filters out over 70% of solar ultraviolet, especially at
447-403: A fairly small amount of power being generated per cubic metre . Theoretical models of the Sun's interior indicate a maximum power density, or energy production, of approximately 276.5 watts per cubic metre at the center of the core, which, according to Karl Kruszelnicki , is about the same power density inside a compost pile . The fusion rate in the core is in a self-correcting equilibrium:
596-414: A few millimeters. Re-emission happens in a random direction and usually at slightly lower energy. With this sequence of emissions and absorptions, it takes a long time for radiation to reach the Sun's surface. Estimates of the photon travel time range between 10,000 and 170,000 years. In contrast, it takes only 2.3 seconds for neutrinos , which account for about 2% of the total energy production of
745-401: A granular appearance called the solar granulation at the smallest scale and supergranulation at larger scales. Turbulent convection in this outer part of the solar interior sustains "small-scale" dynamo action over the near-surface volume of the Sun. The Sun's thermal columns are Bénard cells and take the shape of roughly hexagonal prisms. The visible surface of the Sun, the photosphere,
894-479: A half millennia . It began with the incipient unification of Nile Valley polities around 3100 BC, traditionally under Menes . The civilisation of ancient Egypt was characterised primarily by intensive agricultural use of the fertile Nile Valley; the use of the Nile itself for transportation; the development of writing systems – first hieroglyphs and then later hieratic and other derived scripts – and literature ;
1043-496: A large kingdom at three different times in history. These are called the Old (20th to 18th centuries BC), Middle (14th to 11th centuries BC), and Neo-Assyrian (9th to 7th centuries BC) kingdoms, or periods. Mitanni was a Hurrian empire in northern Mesopotamia founded around 1500 BC. The Mitanians conquered and controlled Assyria until the 14th century BC while contending with Egypt for control of parts of modern Syria. Its capital
1192-589: A later emperor, Darius the Great , expanded the empire to the Indus River , creating the largest empire in the world to that date. But Darius and his son Xerxes I failed to expand into Greece , with expeditions in 490 and 480 BC eventually failing. The Achaemenid dynasty and empire fell to Alexander the Great by 330 BC, and after Alexander's death, much of the area previously ruled by the Cyrus and his successors
1341-451: A number of dynasties that peaked in power under the reign of Ashoka Maurya, one of India's most legendary and famous emperors. During the reign of Ashoka, the four dynasties of Chola , Chera , and Pandya were ruling in the South, while Devanampiya Tissa (250–210 BC) controlled Anuradhapura (now Sri Lanka ). These kingdoms, while not part of Ashoka's empire, were in friendly terms with
1490-520: A period known as the Maunder minimum . This coincided in time with the era of the Little Ice Age , when Europe experienced unusually cold temperatures. Earlier extended minima have been discovered through analysis of tree rings and appear to have coincided with lower-than-average global temperatures. The temperature of the photosphere is approximately 6,000 K, whereas the temperature of
1639-522: A period often known as the Vedic period . Between 1500 and 500 BC these peoples spread throughout most of India and had begun to found small cities. Vedic society was characterized by the varna system which divided society into four broad castes, which were later elaborated. By the end of the Vedic period, this way of organizing society had become central to Indian society. Religion in the late Vedic period
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#17327919495761788-485: A phenomenon described by Hale's law . During the solar cycle's declining phase, energy shifts from the internal toroidal magnetic field to the external poloidal field, and sunspots diminish in number and size. At solar-cycle minimum, the toroidal field is, correspondingly, at minimum strength, sunspots are relatively rare, and the poloidal field is at its maximum strength. With the rise of the next 11-year sunspot cycle, differential rotation shifts magnetic energy back from
1937-473: A result, the outward-flowing solar wind stretches the interplanetary magnetic field outward, forcing it into a roughly radial structure. For a simple dipolar solar magnetic field, with opposite hemispherical polarities on either side of the solar magnetic equator, a thin current sheet is formed in the solar wind. At great distances, the rotation of the Sun twists the dipolar magnetic field and corresponding current sheet into an Archimedean spiral structure called
2086-410: 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 density and hence the fusion rate and correcting the perturbation ; and a slightly lower rate would cause the core to cool and shrink slightly, increasing the density and increasing the fusion rate and again reverting it to its present rate. The radiative zone
2235-456: A tradition of bronze production and the manufacture of evermore refined bronze and iron objects, such as plows, axes and sickles with shaft holes, socketed arrows and spearheads and small ornamented items. By about 500 BCE, large and delicately decorated bronze drums of remarkable quality, weighing more than 70 kg (150 lb), were produced in the laborious lost-wax casting process. This industry of highly sophisticated metal processing
2384-406: A transition layer, the tachocline . 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 between the two—a condition where successive horizontal layers slide past one another. Presently, it is hypothesized that a magnetic dynamo, or solar dynamo , within this layer generates
2533-528: Is Harappan, after the first of its cities to be excavated, Harappa in the Pakistani province of Punjab . Harappan civilization grew out of the earlier agricultural communities as they evolved into cities. These communities created and traded jewelry, figurines, and seals that appear widely scattered throughout Mesopotamia, Afghanistan, and Iran. Chickens were domesticated in addition to the earlier crops and animals. They developed their own writing system,
2682-555: Is a G-type main-sequence star (G2V), informally called a yellow dwarf , though its light is actually white. It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud . Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System . The central mass became so hot and dense that it eventually initiated nuclear fusion in its core . Every second,
2831-444: Is a time period from the beginning of writing and recorded human history through late antiquity . The span of recorded history is roughly 5,000 years, beginning with the development of Sumerian cuneiform script. Ancient history covers all continents inhabited by humans in the period 3000 BC – AD 500, ending with the expansion of Islam in late antiquity. The three-age system periodizes ancient history into
2980-405: Is about 1,391,400 km ( 864,600 mi ), 109 times that of Earth. Its mass is about 330,000 times that of Earth, making up about 99.86% of the total mass of the Solar System. Roughly three-quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen , carbon , neon , and iron . The Sun
3129-643: Is by far the brightest object in the Earth's sky , with an apparent magnitude of −26.74. This is about 13 billion times brighter than the next brightest star, Sirius , which has an apparent magnitude of −1.46. One astronomical unit (about 150 million kilometres; 93 million miles) is defined as the mean distance between the centres of the Sun and the Earth. The instantaneous distance varies by about ± 2.5 million km or 1.55 million miles as Earth moves from perihelion on ~ January 3rd to aphelion on ~ July 4th. At its average distance, light travels from
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#17327919495763278-474: Is by far the most important source of energy for life on Earth . The Sun has been an object of veneration in many cultures. It has been a central subject for astronomical research since antiquity . The Sun orbits the Galactic Center at a distance of 24,000 to 28,000 light-years . From Earth, it is 1 astronomical unit ( 1.496 × 10 km ) or about 8 light-minutes away. Its diameter
3427-436: Is defined to begin at the distance where the flow of the solar wind becomes superalfvénic —that is, where the flow becomes faster than the speed of Alfvén waves, at approximately 20 solar radii ( 0.1 AU ). Turbulence and dynamic forces in the heliosphere 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
3576-402: Is facilitated by the full ionization of helium in the transition region, which significantly reduces radiative cooling of the plasma. The transition region does not occur at a well-defined altitude, but forms a kind of nimbus around chromospheric features such as spicules and filaments , and is in constant, chaotic motion. The transition region is not easily visible from Earth's surface, but
3725-637: Is managed by the National Solar Observatory Integrated Synoptic Program (NISP), which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation . GONG has been in operation since 1995 and is aging rapidly. To replace it, NSO is proposing to design and build a next-generation Ground-based solar Observing Network, provisionally named ngGONG. In April 2023, NOAA Science Advisory Board reported on
3874-409: Is only 84% of what it was in the protostellar phase (before nuclear fusion in the core started). In the future, helium will continue to accumulate in the core, and in about 5 billion years this gradual build-up will eventually cause the Sun to exit the main sequence and become a red giant . The chemical composition of the photosphere is normally considered representative of the composition of
4023-441: Is readily observable from space by instruments sensitive to extreme ultraviolet . The corona is the next layer of the Sun. The low corona, near the surface of the Sun, has a particle density around 10 m to 10 m . The average temperature of the corona and solar wind is about 1,000,000–2,000,000 K; however, in the hottest regions it is 8,000,000–20,000,000 K. Although no complete theory yet exists to account for
4172-410: Is strongly attenuated by Earth's ozone layer , so that the amount of UV varies greatly with latitude and has been partially responsible for many biological adaptations, including variations in human skin color . High-energy gamma ray photons initially released with fusion reactions in the core are almost immediately absorbed by the solar plasma of the radiative zone, usually after traveling only
4321-422: Is suggested by a high abundance of heavy elements in the Solar System, such as gold and uranium , relative to the abundances of these elements in so-called Population II , heavy-element-poor, stars. The heavy elements could most plausibly have been produced by endothermic nuclear reactions during a supernova, or by transmutation through neutron absorption within a massive second-generation star. The Sun
4470-470: Is tens to hundreds of kilometers thick, and is slightly less opaque than air on Earth. 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 . The spectrum of sunlight has approximately the spectrum of a black-body radiating at 5,772 K (9,930 °F), interspersed with atomic absorption lines from
4619-437: Is the layer below which the Sun becomes opaque to visible light. Photons produced in this layer escape the Sun through the transparent solar atmosphere above it and become solar radiation, sunlight. The change in opacity is due to the decreasing amount of H ions , which absorb visible light easily. Conversely, the visible light perceived is produced as electrons react with hydrogen atoms to produce H ions. The photosphere
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4768-424: Is the most prominent variation in which the number and size of sunspots waxes and wanes. The solar magnetic field extends well beyond the Sun itself. The electrically conducting solar wind plasma carries the Sun's magnetic field into space, forming what is called the interplanetary magnetic field . In an approximation known as ideal magnetohydrodynamics , plasma particles only move along magnetic field lines. As
4917-531: Is the only region of the Sun that produces an appreciable amount of thermal energy through fusion; 99% of the Sun's power is generated in the innermost 24% of its radius, and almost no fusion occurs beyond 30% of the radius. The rest of the Sun is heated by this energy as it is transferred outward through many successive layers, finally to the solar photosphere where it escapes into space through radiation (photons) or advection (massive particles). The proton–proton chain occurs around 9.2 × 10 times each second in
5066-420: Is the thickest layer of the Sun, at 0.45 solar radii. From the core out to about 0.7 solar radii , thermal radiation is the primary means of energy transfer. The temperature drops from approximately 7 million to 2 million kelvins with increasing distance from the core. This temperature gradient is less than the value of the adiabatic lapse rate and hence cannot drive convection, which explains why
5215-444: Is theorized to become a super dense black dwarf , giving off negligible energy. The English word sun developed from Old English sunne . Cognates appear in other Germanic languages , including West Frisian sinne , Dutch zon , Low German Sünn , Standard German Sonne , Bavarian Sunna , Old Norse sunna , and Gothic sunnō . All these words stem from Proto-Germanic * sunnōn . This
5364-538: Is ultimately related to the word for sun in other branches of the Indo-European language family, though in most cases a nominative stem with an l is found, rather than the genitive stem in n , as for example in Latin sōl , ancient Greek ἥλιος ( hēlios ), Welsh haul and Czech slunce , as well as (with *l > r ) Sanskrit स्वर् ( svár ) and Persian خور ( xvar ). Indeed,
5513-402: Is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone. These waves travel upward and dissipate in the corona, depositing their energy in the ambient matter 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
5662-520: Is yet to be confirmed with extensive survey work. With the help of archaeological excavations mainly by Susan and Roderick McIntosh , the site is known to have been occupied from 250 BC to AD 900. The city is believed to have been abandoned and moved where the current city is located due to the spread of Islam and the building of the Great Mosque of Djenné . Previously, it was assumed that advanced trade networks and complex societies did not exist in
5811-547: The Alfvén surface , the boundary separating the corona from the solar wind, defined as where the coronal plasma's Alfvén speed and the large-scale solar wind speed are equal. During the flyby, Parker Solar Probe passed into and out of the corona several times. This proved the predictions that the Alfvén critical surface is not shaped like a smooth ball, but has spikes and valleys that wrinkle its surface. The Sun emits light across
5960-569: The Chaldeans in 614 BC. The Achaemenid Empire was founded by Cyrus the Great , who first became king of the Persians, then conquered the Medes, Lydia , and Babylon by 539 BC. The empire built on earlier Mesopotamian systems of government to govern their large empire. By building roads, they improved both the ability to send governmental instructions throughout their lands as well as improving
6109-763: The Congo River and into the Great Lakes area. By AD 1000 these groups had spread throughout all of southern Africa south of the equator. Iron metallurgy and agriculture spread along with these peoples, with the cultivation of millet, oil palms, sorghum, and yams as well as the use of domesticated cattle, pigs, and sheep. These technologies helped increase population, and settled communities became common in sub-Saharan Africa except in deserts or heavy forests. Paleolithic tools have been discovered in India dating to 200,000 years ago, and Neolithic sites are known from near
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6258-681: The Indus Valley dating to around 8000 BC. Agriculture began in the Indus Valley around 7000 BC, and reached the Ganges Valley by 3000 BC. Barley , cotton , and wheat were grown and the population had domesticated cattle, goats, and sheep. The Indus Valley Civilisation developed around 3000 BC in the Indus and Ghaggar-Hakra river valleys of eastern Afghanistan , Pakistan, and western India. Another name for this civilisation
6407-495: The Indus Valley script , which is still mostly undeciphered. The exact structure of society and the way the cities were governed is not known. By about 1600 BC, the Indus Valley culture had abandoned many of their cities, including Mohenjo-Daro . The exact reason for this decline is not known. Indo-European speaking peoples began to spread into India about 1500 BC. The Rigveda , in Sanskrit , dates to this period and begins
6556-587: The Maccabean revolt led to independence during Hellenistic period until Roman conquest . Phoenicia was an ancient civilisation centered in the north of ancient Canaan , with its heartland along the coastal regions of modern-day Lebanon , Syria and Israel. Phoenician civilisation was an enterprising maritime trading culture that spread across the Mediterranean between the period of 1550 to 300 BC. One Phoenician colony, Carthage , ruled an empire in
6705-802: The Maritime Jade Road , a jade trade network, in Southeast Asia which existed in Taiwan and the Philippines for 3,000 years from 2000 BCE to 1000 CE. The trade was established by links between the indigenous peoples of Taiwan and the Philippines, and later included parts of Vietnam, Malaysia, Indonesia, Thailand, and other areas in Southeast Asia (known as the Sa Huynh - Kalanay Interaction Sphere). Lingling-o artifacts are one of
6854-603: The Maurya Empire . An alliance existed between Devanampiya Tissa and Ashoka of India, who sent Buddhist missionaries to Sri Lanka. Most of North India was reunited under the Gupta Empire beginning under Chandragupta I around AD 320. Under his successors the empire spread to include much of India except for the Deccan Plateau and the very south of the peninsula. This was a period of relative peace, and
7003-778: The Nile Delta in the north, as far south as Jebel Barkal at the Fourth Cataract of the Nile. Extensions to the geographical range of ancient Egyptian civilisation included, at different times, areas of the southern Levant , the Eastern Desert and the Red Sea coastline, the Sinai Peninsula , and the Western Desert (focused on the several oases ). Ancient Egypt developed over at least three and
7152-688: The Old Kingdom , which saw pyramid building on a large scale. After 2100 BC, the Old Kingdom dissolved into smaller states during the First Intermediate Period , which lasted about 100 years. The Middle Kingdom began around 2000 BC with the reunification of Egypt under pharoes ruling from Thebes . The Middle Kingdom ended with the conquest of northern Egypt by the Hyksos around 1650 BC. The Hyksos were expelled from Egypt and
7301-524: The Parker spiral . Sunspots are visible as dark patches on the Sun's photosphere and correspond to concentrations of magnetic field where convective transport of heat is inhibited from the solar interior to the surface. As a result, sunspots are slightly cooler than the surrounding photosphere, so they appear dark. At a typical solar minimum , few sunspots are visible, and occasionally none can be seen at all. Those that do appear are at high solar latitudes. As
7450-827: The Pitcairns , the Kermadec Islands , and the Norfolk Islands were also formerly settled by Austronesians but later abandoned. There is also putative evidence, based in the spread of the sweet potato , that Austronesians may have reached South America from Polynesia, where they might have traded with the Indigenous peoples of the Americas . Austronesians established prehistoric maritime trade networks in Island Southeast Asia, including
7599-845: The Seleucid Empire . Parthia had many wars with the Romans, but it was rebellions within the empire that ended it in the 3rd century AD. The Sasanian Empire began when the Parthian Empire ended in AD 224. Their rulers claimed the Achaemenids as ancestors and set up their capital at Ctesiphon in Mesopotamia. Their period of greatest military expansion occurred under Shapur I , who by the time of his death in AD 272 had defeated Roman imperial armies and set up buffer states between
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#17327919495767748-713: The Stone Age , the Bronze Age , and the Iron Age , with recorded history generally considered to begin with the Bronze Age. The start and end of the three ages vary between world regions. In many regions the Bronze Age is generally considered to begin a few centuries prior to 3000 BC, while the end of the Iron Age varies from the early first millennium BC in some regions to the late first millennium AD in others. During
7897-496: The Zapotec civilization . The ancient Near East is considered the cradle of civilization . It was the first to practice intensive year-round agriculture; created one of the first coherent writing systems , invented the potter's wheel and then the vehicular wheel , created the first centralized governments , law codes and empires, as well as displaying social stratification , slavery, and organized warfare. It began
8046-410: The corona , and the heliosphere . The coolest layer of the Sun is a temperature minimum region extending to about 500 km above the photosphere, and has a temperature of about 4,100 K . This part of the Sun is cool enough to allow for the existence of simple molecules such as carbon monoxide and water. The chromosphere, transition region, and corona are much hotter than the surface of
8195-614: The l -stem survived in Proto-Germanic as well, as * sōwelan , which gave rise to Gothic sauil (alongside sunnō ) and Old Norse prosaic sól (alongside poetic sunna ), and through it the words for sun in the modern Scandinavian languages: Swedish and Danish sol , Icelandic sól , etc. The principal adjectives for the Sun in English are sunny for sunlight and, in technical contexts, solar ( / ˈ s oʊ l ər / ), from Latin sol . From
8344-428: The photosphere . For the purpose of measurement, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun. By this measure, the Sun is a near-perfect sphere with an oblateness estimated at 9 millionths, which means that its polar diameter differs from its equatorial diameter by only 10 kilometers (6.2 mi). The tidal effect of
8493-444: The visible spectrum , so its color is white , with a CIE color-space index near (0.3, 0.3), when viewed from space or when the Sun is high in the sky. The Solar radiance per wavelength peaks in the green portion of the spectrum when viewed from space. When the Sun is very low in the sky, atmospheric scattering renders the Sun yellow, red, orange, or magenta, and in rare occasions even green or blue . Some cultures mentally picture
8642-575: The Assyrians, who conquered Israel in 722 BC. The Neo-Babylonian Empire did the same to Judah in 586. After both conquests, the conquering forces deported many of the inhabitants to other regions of their respective empires. Following the fall of Babylon to the Persian Empire, Cyrus the Great allowed the rebuilding of the temple at Jerusalem , and some of the exiles from Judah returned to Judea , where they remained under Persian rule until
8791-907: The Earth so that the Sun can be observed as continuously as possible. The six observatories are the Teide Observatory ( Canary Islands ), the Learmonth Solar Observatory ( Western Australia ), the Big Bear Solar Observatory ( California ), the Mauna Loa Observatory ( Hawaii ), the Udaipur Solar Observatory ( India ) and the Cerro Tololo Inter-American Observatory ( Chile ). With these sites, GONG typically can observe
8940-650: The Egyptians as a possible challenge to their hegemony , but an ethnic group rather than an organised state. Israel had emerged by the middle of the 9th century BC, when the Assyrian King Shalmaneser III named " Ahab the Israelite" among his enemies at the battle of Qarqar (853). Judah emerged somewhat later than Israel, probably during the 9th century BC, but the subject is one of considerable controversy. Israel came into conflict with
9089-518: The Fertile Crescent, alongside the first evidence for agriculture. Other animals, such as pigs and poultry , were later domesticated and used as food sources. Cattle and water buffalo were domesticated around 7000 BC and horses , donkeys , and camels were domesticated by about 4000 BC. All of these animals were used not only for food, but to carry and pull people and loads, greatly increasing human ability to do work. The invention of
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#17327919495769238-465: The Greek helios comes the rare adjective heliac ( / ˈ h iː l i æ k / ). In English, the Greek and Latin words occur in poetry as personifications of the Sun, Helios ( / ˈ h iː l i ə s / ) and Sol ( / ˈ s ɒ l / ), while in science fiction Sol may be used to distinguish the Sun from other stars. The term sol with a lowercase s is used by planetary astronomers for
9387-613: The Gupta rulers generally left administration in local rulers. The Gupta Empire was weakened and ultimately ruined by the raids of Hunas (a branch of the Hephthalites emanating from Central Asia), and the empire broke up into smaller regional kingdoms by the end of the fifth century AD. India would remain fragmented into smaller states until the rise of the Mughal Empire in the 1500s. The Neolithic period of Southeast Asia
9536-889: The Malayan-Indonesian " thalassian " zone shared these characteristics with Indochinese polities like the Pyu city-states in the Irrawaddy River valley, the Văn Lang kingdom in the Red River Delta and Funan around the lower Mekong . Văn Lang, founded in the 7th century BCE, endured until 258 BCE under the Hồng Bàng dynasty , as part of the Đông Sơn culture that sustained a dense and organised population that produced an elaborate Bronze Age industry. Intensive wet-rice cultivation in an ideal climate enabled
9685-768: The Middle East. Egypt developed its own system of hieroglyphs by about 3200 BC. By 2800 BC the Indus Valley Civilization had developed its Indus script , which remains undeciphered. Chinese Characters were independently developed in China during the Shang dynasty in the form of the Oracle Bone Script dating to the period 1600 to 1100 BC. Writing in Mesoamerica dates to 600 BC with
9834-408: The Nubians had created a new kingdom further south, known as the Kingdom of Kush , centred on the upper Nile with a capital at Kerma . In the Egyptian New Kingdom period, Kush once more was conquered by Egypt. However, by 1100 BC a new kingdom of Kush had formed, with a capital at Napata . Nubian rulers conquered Egypt around 760 BC and retained control for about a century. The Kingdom of Aksum
9983-472: The Pacific Islands to successfully retain rice cultivation. Palau and Yap were settled by separate voyages by 1000 BCE. Another important migration branch was by the Lapita culture , which rapidly spread into the islands off the coast of northern New Guinea and into the Solomon Islands and other parts of coastal New Guinea and Island Melanesia by 1200 BCE. They reached the islands of Fiji , Samoa , and Tonga by around 900 to 800 BCE. This remained
10132-401: The Sasanians and Roman Empires. After Shapur, the Sasanians were under more pressure from the Kushans to their east as well as the Roman then Byzantine Empire to its west. However, the Sasanians rebuilt and founded numerous cities and their merchants traveled widely and introduced crops such as sugar, rice, and cotton into the Iranian plateau. But in AD 651, the last Sassanid emperor was killed by
10281-446: The Solar System . Long-term secular change in sunspot number is thought, by some scientists, to be correlated with long-term change in solar irradiance, which, in turn, might influence Earth's long-term climate. The solar cycle influences space weather conditions, including those surrounding Earth. For example, in the 17th century, the solar cycle appeared to have stopped entirely for several decades; few sunspots were observed during
10430-510: The Sun 91% of the time, 24/7. GONG was constructed to provide observations for helioseismology, which aims to understand the solar interior by analyzing the sound waves that are trapped in it. In 2001, the original GONG detectors were upgraded to 1000 x 1000 pixels and continuous magnetograms were implemented, and the new system is known as GONG++. While GONG still provides helioseismology data, it now also provides full-disk solar magnetic field maps (magnetograms) every minute and full-disk images of
10579-443: The Sun as yellow and some even red; the cultural reasons for this are debated. The Sun is classed as a G2 star, meaning it is a G-type star , with 2 indicating its surface temperature is in the second range of the G class. 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 1,368 W/m (watts per square meter) at
10728-424: The Sun extends from the center to about 20–25% of the solar radius. It has a density of up to 150 g/cm (about 150 times the density of water) and a temperature of close to 15.7 million kelvin (K). By contrast, the Sun's surface temperature is about 5800 K . Recent analysis of SOHO mission data favors the idea that the core is rotating faster than the radiative zone outside it. Through most of
10877-676: The Sun in the wavelength of the Hydrogen–α (Hα) spectral line every 20 seconds. These data products are used for research into the solar magnetic field and chromosphere but are also essential inputs into forecasts of space weather. The NOAA Space Weather Prediction Center (SWPC), the US Airforce 557th Weather Wing , and the NASA Community Coordinated Modeling Center (CCMC) all use GONG data to predict space weather conditions. The GONG Project
11026-438: The Sun into a red giant . This process will make the Sun large enough to render Earth uninhabitable approximately five billion years from the present. After the red giant phase, models suggest the Sun will shed its outer layers and become a dense type of cooling star (a white dwarf ), and no longer produce energy by fusion, but will still glow and give off heat from its previous fusion for perhaps trillions of years. After that, it
11175-413: The Sun's magnetic field . The Sun's convection zone extends from 0.7 solar radii (500,000 km) to near the surface. In this layer, the solar plasma is not dense or hot enough to transfer the heat energy of the interior outward via radiation. Instead, the density of the plasma is low enough to allow convective currents to develop and move the Sun's energy outward towards its surface. Material heated at
11324-398: The Sun's core by radiation rather than by convection (see Radiative zone below), so the fusion products are not lifted outward by heat; they remain in the core, and gradually an inner core of helium has begun to form that cannot be fused because presently the Sun's core is not hot or dense enough to fuse helium. In the current photosphere, the helium fraction is reduced, and the metallicity
11473-437: The Sun's core fuses about 600 billion kilograms (kg) of hydrogen into helium and converts 4 billion kg of matter into energy . About 4 to 7 billion years from now, when hydrogen fusion in the Sun's core diminishes to the point where the Sun is no longer in hydrostatic equilibrium , its core will undergo a marked increase in density and temperature which will cause its outer layers to expand, eventually transforming
11622-403: The Sun's horizon to Earth's horizon in about 8 minutes and 20 seconds, while light from the closest points of the Sun and Earth takes about two seconds less. The energy of this sunlight supports almost all life on Earth by photosynthesis , and drives Earth's climate and weather. The Sun does not have a definite boundary, but its density decreases exponentially with increasing height above
11771-499: The Sun's life, energy has been produced by nuclear fusion in the core region through the proton–proton chain ; this process converts hydrogen into helium. Currently, 0.8% of the energy generated in the Sun comes from another sequence of fusion reactions called the CNO cycle ; the proportion coming from the CNO cycle is expected to increase as the Sun becomes older and more luminous. The core
11920-551: The Sun's life, they account for 74.9% and 23.8%, respectively, of the mass of the Sun in the photosphere. All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant. The Sun's original chemical composition was inherited from the interstellar medium out of which it formed. Originally it would have been about 71.1% hydrogen, 27.4% helium, and 1.5% heavier elements. The hydrogen and most of
12069-438: The Sun, to reach the surface. Because energy transport in the Sun is a process that involves photons in thermodynamic equilibrium with matter , the time scale of energy transport in the Sun is longer, on the order of 30,000,000 years. This is the time it would take the Sun to return to a stable state if the rate of energy generation in its core were suddenly changed. Electron neutrinos are released by fusion reactions in
12218-402: The Sun. The reason is not well understood, but evidence suggests that Alfvén waves may have enough energy to heat the corona. Above the temperature minimum layer is a 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
12367-667: The Western Mediterranean until being defeated by Rome in the Punic Wars . The Phoenicians invented the Phoenician alphabet , the forerunner of the modern alphabet still in use today. The history of Pre-Islamic Arabia before the rise of Islam in the AD 630s is not known in great detail. Archaeological exploration in the Arabian Peninsula has been sparse; indigenous written sources are limited to
12516-492: The ability of their military forces to be deployed rapidly. Increased trade and upgraded farming techniques increased wealth, but also exacerbated inequalities between social classes. The empire's location at the centre of trading networks spread its intellectual and philosophical ideas throughout a wide area, and its religion, while not itself spreading far, had an impact on later religions such as Christianity , Islam , and Judaism . Cyrus' son Cambyses II conquered Egypt, while
12665-492: The archipelago of the Philippines , intermingling with the earlier Australo-Melanesian population who had inhabited the islands since about 23,000 years earlier. Over the next thousand years, Austronesian peoples migrated southeast to the rest of the Philippines, and into the islands of the Celebes Sea and Borneo. From southwestern Borneo, Austronesians spread further west in a single migration event to both Sumatra and
12814-486: The beginning and end of total solar eclipses. The temperature of the chromosphere increases gradually with altitude, ranging up to around 20,000 K near the top. In the upper part of the chromosphere helium becomes partially ionized . Above the chromosphere, in a thin (about 200 km ) transition region, the temperature rises rapidly from around 20,000 K in the upper chromosphere to coronal temperatures closer to 1,000,000 K . The temperature increase
12963-527: The capital of the Akkadian Empire. Despite an extensive search, the precise site has never been found. Akkad reached the height of its power between about 2330 and 2150 BC, following the conquests of King Sargon of Akkad . Through the spread of Sargon's empire, the language of Akkad, known as Akkadian from the city, spread and replaced the Sumerian language in Mesopotamia and eventually by 1450 BC
13112-570: The casting of iron with molds and then hammering it which enabled weapons and tools to be made stronger and also cheaper. Although chariots had been used previously, the use of spoked wheels allowed the chariots to be much lighter and more maneuverable. In 1274 BC the Hittites clashed with the Egyptians at the Battle of Kadesh , where both sides claimed victory. In 1207 the Hittite capital of Hattusa
13261-614: The coastal regions of southern Vietnam, becoming the ancestors of the speakers of the Malayic and Chamic branches of the Austronesian language family. Soon after reaching the Philippines, Austronesians colonized the Northern Mariana Islands by 1500 BCE or even earlier, becoming the first humans to reach Remote Oceania . The Chamorro migration was also unique in that it was the only Austronesian migration to
13410-460: The core, but, unlike photons, they rarely interact with matter, so almost all are able to escape the Sun immediately. However, measurements of the number of these neutrinos produced in the Sun are lower than theories predict by a factor of 3. In 2001, the discovery of neutrino oscillation resolved the discrepancy: the Sun emits the number of electron neutrinos predicted by the theory, but neutrino detectors were missing 2 ⁄ 3 of them because
13559-501: The core, converting about 3.7 × 10 protons into alpha particles (helium nuclei) every second (out of a total of ~8.9 × 10 free protons in the Sun), or about 6.2 × 10 kg/s . However, each proton (on average) takes around 9 billion years to fuse with another using the PP chain. Fusing four free protons (hydrogen nuclei) into a single alpha particle (helium nucleus) releases around 0.7% of
13708-401: The corona reaches 1,000,000–2,000,000 K . The high temperature of the corona shows that it is heated by something other than direct heat conduction from the photosphere. 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
13857-553: The demise of GONG is closing." The Board recommended that "NOAA/NWS financially support the design phase for ngGONG, to insure the initiation of the project." Sun The Sun is the star at the center of the Solar System . It is a massive, nearly perfect sphere of hot plasma , heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light and infrared radiation with 10% at ultraviolet energies. It
14006-400: The duration of a solar day on another planet such as Mars . The astronomical symbol for the Sun is a circle with a center dot, [REDACTED] . It is used for such units as M ☉ ( Solar mass ), R ☉ ( Solar radius ) and L ☉ ( Solar luminosity ). The scientific study of the Sun is called heliology . The Sun is a G-type main-sequence star that makes up about 99.86% of
14155-538: The empire was Aksum , now in northern Ethiopia. The Nok culture appeared in Nigeria around 1000 BC and mysteriously vanished around AD 200. The civilisation's social system is thought to have been highly advanced. The Nok civilisation was considered to be the earliest sub-Saharan producer of life-sized Terracotta which have been discovered by archaeologists. The Nok also used iron smelting that may have been independently developed. The civilisation of Djenné-Djenno
14304-498: The entire territory. Among large, thin-walled terracotta jars, ornamented and colorized cooking pots, glass items, jade earrings and metal objects were deposited near the rivers and along the coast. Around 3000 to 1500 BCE, a large-scale migration of Austronesians , known as the Austronesian expansion began from Taiwan . Population growth primarily fueled this migration. These first settlers settled in northern Luzon , in
14453-486: The expanding Islamic Arabs. The Hittites first came to Anatolia about 1900 BC and during the period 1600-1500 they expanded into Mesopotamia where they adopted the cuneiform script to their Indo-European language. By 1200 their empire stretched to Phoenicia and eastern Anatolia . They improved two earlier technologies from Mesopotamia and spread these new techniques widely – improved iron working and light chariots with spoked wheels in warfare. The Hittites introduced
14602-563: The external poloidal dipolar magnetic field is near its dynamo-cycle minimum strength; but an internal toroidal quadrupolar field, generated through differential rotation within the tachocline, is near its maximum strength. At this point in the dynamo cycle, buoyant upwelling within the convective zone forces emergence of the toroidal magnetic field through the photosphere, giving rise to pairs of sunspots, roughly aligned east–west and having footprints with opposite magnetic polarities. The magnetic polarity of sunspot pairs alternates every solar cycle,
14751-521: The farming communities to produce a regular crop surplus that was used by the ruling elite to raise, command and pay work forces for public construction and maintenance projects such as canals and fortifications. The earliest known evidence of copper and bronze production in Southeast Asia was found at Ban Chiang in north-east Thailand and among the Phùng Nguyên culture of northern Vietnam around 2000 BCE. The Đông Sơn culture established
14900-448: The form of large solar flares and myriad similar but smaller events— nanoflares . 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. In addition, Alfvén waves do not easily dissipate in the corona. Current research focus has therefore shifted towards flare heating mechanisms. Ancient history Ancient history
15049-687: The furthest extent of the Austronesian expansion into Polynesia until around 700 CE, when there was another surge of island colonization. It reached the Cook Islands , Tahiti , and the Marquesas by 700 CE; Hawaii by 900 CE; Rapa Nui by 1000 CE; and New Zealand by 1200 CE. For a few centuries, the Polynesian islands were connected by bidirectional long-distance sailing, with the exception of Rapa Nui, which had limited further contact due to its isolated geographical location. Island groups like
15198-404: The fused mass as energy, so the Sun releases energy at the mass–energy conversion rate of 4.26 billion kg/s (which requires 600 billion kg of hydrogen ), for 384.6 yottawatts ( 3.846 × 10 W ), or 9.192 × 10 megatons of TNT per second. The large power output of the Sun is mainly due to the huge size and density of its core (compared to Earth and objects on Earth), with only
15347-482: The heliosphere, forming the solar magnetic field into a spiral shape, until it impacts the heliopause more than 50 AU from the Sun. In December 2004, the Voyager 1 probe passed through a shock front that is thought to be part of the heliopause. In late 2012, Voyager 1 recorded a marked increase in cosmic ray collisions and a sharp drop in lower energy particles from the solar wind, which suggested that
15496-432: The helium in the Sun would have been produced by Big Bang nucleosynthesis in the first 20 minutes of the universe, and the heavier elements were produced by previous generations of stars before the Sun was formed, and spread into the interstellar medium during the final stages of stellar life and by events such as supernovae . Since the Sun formed, the main fusion process has involved fusing hydrogen into helium. Over
15645-401: The importance of GONG and its successor data source for space weather operations. It concluded that "GONG provides a vital data source for space weather operations, and it is nearing end of life. The ngGONG project is the most straightforward replacement. It will maintain present operational capabilities, and provide observations for future requirements. The time window to complete ngGONG prior to
15794-555: The land was reunited in the New Kingdom around 1550 BC. This period lasted until about 1000 BC, and saw Egypt expand its borders into Palestine and Syria. The Third Intermediate Period was marked by the rule of priests as well as the conquest of Egypt by Nubian kings and then later Assyria, Persia, and Macedonians. The Ta-Seti kingdom in Nubia to the south of Egypt was conquered by Egyptian rulers around 3100 BC, but by 2500 BC
15943-467: The many inscriptions and coins from southern Arabia. Existing material consists primarily of written sources from other traditions (such as Egyptians, Greeks, Persians, Romans, etc.) and oral traditions later recorded by Islamic scholars. A number of small kingdoms existed in Arabia from around AD 100 to perhaps about AD 400. Carthage was founded around 814 BC by Phoenician settlers. Ancient Carthage
16092-505: The mass of the Solar System. It has an absolute magnitude of +4.83, estimated to be brighter than about 85% of the stars in the Milky Way , most of which are red dwarfs . It is more massive than 95% of the stars within 7 pc (23 ly). The Sun is a Population I , or heavy-element-rich, star. Its formation approximately 4.6 billion years ago may have been triggered by shockwaves from one or more nearby supernovae . This
16241-444: The neutrinos had changed flavor by the time they were detected. The Sun has a stellar magnetic field that varies across its surface. Its polar field is 1–2 gauss (0.0001–0.0002 T ), whereas the field is typically 3,000 gauss (0.3 T) in features on the Sun called sunspots and 10–100 gauss (0.001–0.01 T) in solar prominences . The magnetic field varies in time and location. The quasi-periodic 11-year solar cycle
16390-442: The organisation of collective projects such as the pyramids ; trade with surrounding regions; and a polytheistic religious tradition that included elaborate funeral customs including mummification . Overseeing these activities were a socio-political and economic elite under the figure of a (semi)-divine ruler from a succession of ruling dynasties . Ancient Egyptian history is divided across various periods, beginning with
16539-419: The past 4.6 billion years, the amount of helium and its location within the Sun has gradually changed. The proportion of helium within the core has increased from about 24% to about 60% due to fusion, and some of the helium and heavy elements have settled from the photosphere toward the center of the Sun because of gravity . The proportions of heavier elements are unchanged. Heat is transferred outward from
16688-414: The photospheric surface. Both coronal mass ejections and high-speed streams of solar wind carry plasma and the interplanetary magnetic field outward into the Solar System. The effects of solar activity on Earth include auroras at moderate to high latitudes and the disruption of radio communications and electric power . Solar activity is thought to have played a large role in the formation and evolution of
16837-455: The planets is weak and does not significantly affect the shape of the Sun. The Sun rotates faster at its equator than at its poles . This differential rotation is caused by convective motion due to heat transport and the Coriolis force due to the Sun's rotation. In a frame of reference defined by the stars, the rotational period is approximately 25.6 days at the equator and 33.5 days at
16986-473: The poles. Viewed from Earth as it orbits the Sun, the apparent rotational period of the Sun at its equator is about 28 days. Viewed from a vantage point above its north pole, the Sun rotates counterclockwise around its axis of spin. A survey of solar analogs suggest the early Sun was rotating up to ten times faster than it does today. This would have made the surface much more active, with greater X-ray and UV emission. Sun spots would have covered 5–30% of
17135-557: The poloidal to the toroidal field, but with a polarity that is opposite to the previous cycle. The process carries on continuously, and in an idealized, simplified scenario, each 11-year sunspot cycle corresponds to a change, then, in the overall polarity of the Sun's large-scale magnetic field. The Sun's magnetic field leads to many effects that are collectively called solar activity . Solar flares and coronal mass ejections tend to occur at sunspot groups. Slowly changing high-speed streams of solar wind are emitted from coronal holes at
17284-472: The population to settle in one place instead of migrating after crops and herds. It also allowed for a much greater population density, and in turn required an extensive labour force and division of labour. This organization led to the necessity of record keeping and the development of writing. Babylonia was an Amorite state in lower Mesopotamia (modern southern Iraq ), with Babylon as its capital. Babylonia emerged when Hammurabi created an empire out of
17433-448: The primordial Solar System. Typically, the solar heavy-element abundances described above are measured both by using spectroscopy of the Sun's photosphere and by measuring abundances in meteorites that have never been heated to melting temperatures. These meteorites are thought to retain the composition of the protostellar Sun and are thus not affected by the settling of heavy elements. The two methods generally agree well. The core of
17582-470: The probe had passed through the heliopause and entered the interstellar medium , and indeed did so on August 25, 2012, at approximately 122 astronomical units (18 Tm) from the Sun. The heliosphere has a heliotail which stretches out behind it due to the Sun's peculiar motion through the galaxy. On April 28, 2021, NASA's Parker Solar Probe encountered the specific magnetic and particle conditions at 18.8 solar radii that indicated that it penetrated
17731-567: The region in the former savannah of the Sahara. Its inhabitants fished and grew millet. It has been found that the Soninke of the Mandé peoples were responsible for constructing such settlements. Around 300 BC, the region became more desiccated and the settlements began to decline, most likely relocating to Koumbi Saleh. From the type of architecture and pottery, it is believed that Tichit was related to
17880-634: The region until the arrival of traders from Southwest Asia . However, sites such as Djenné-Djenno disprove this, as these traditions in West Africa flourished long before. Towns similar to that at Djenne-Jeno also developed at the site of Dia, also in Mali along the Niger River , from around 900 BC. Dhar Tichitt and Oualata were prominent among the early urban centres, dated to 2000 BC, in present-day Mauritania. About 500 stone settlements littered
18029-588: The same time period. Cultivation of millet, rice , and legumes began around 7000 BC in China . Taro cultivation in New Guinea dates to about 7000 BC also with squash cultivation in Mesoamerica perhaps sharing that date. Animal domestication began with the domestication of dogs , which dates to at least 15,000 years ago, and perhaps even earlier. Sheep and goats were domesticated around 9000 BC in
18178-684: The same time, southeastern Europe and Siberia around 40,000 years ago, and Japan about 30,000 years ago. Humans migrated to the Americas about 15,000 years ago. Evidence for agriculture emerges in about 9000 BC in what is now eastern Turkey and spread through the Fertile Crescent . Settlement at Göbekli Tepe began around 9500 BC and may have the world's oldest temple. The Nile River Valley has evidence of sorghum and millet cultivation starting around 8000 BC and agricultural use of yams in Western Africa perhaps dates to
18327-437: The shorter wavelengths. Solar ultraviolet radiation ionizes Earth's dayside upper atmosphere, creating the electrically conducting ionosphere . Ultraviolet light from the Sun has antiseptic properties and can be used to sanitize tools and water. This radiation causes sunburn , and has other biological effects such as the production of vitamin D and sun tanning . It is the main cause of skin cancer . Ultraviolet light
18476-471: The simple plough by 6000 BC further increased agricultural efficiency. Metal use in the form of hammered copper items predates the discovery of smelting of copper ores , which happened around 6000 BC in western Asia and independently in eastern Asia before 2000 BC. Gold and silver use dates to between 6000 and 5000 BC. Alloy metallurgy began with bronze in about 3500 BC in Mesopotamia and
18625-425: The solar cycle progresses toward its maximum , sunspots tend to form closer to the solar equator, a phenomenon known as Spörer's law . The largest sunspots can be tens of thousands of kilometers across. An 11-year sunspot cycle is half of a 22-year Babcock –Leighton dynamo cycle, which corresponds to an oscillatory exchange of energy between toroidal and poloidal solar magnetic fields. At solar-cycle maximum,
18774-736: The study of the stars and the sciences of astronomy and mathematics. Mesopotamia is the site of some of the earliest known civilisations in the world. Agricultural communities emerged in the area with the Halaf culture around 8000 BC and continued to expand through the Ubaid period around 6000 BC. Cities began in the Uruk period (4000–3100 BC) and expanded during the Jemdet Nasr (3100–2900 BC) and Early Dynastic (2900–2350 BC) periods. The surplus of storable foodstuffs created by this economy allowed
18923-439: The subsequent Ghana Empire. Old Jenne (Djenne) began to be settled around 300 BC, producing iron and with sizeable population, evidenced in crowded cemeteries. The inhabitants and creators of these settlements during these periods are thought to have been ancestors of the Soninke people. Peoples speaking precursors to the modern-day Bantu languages began to spread throughout southern Africa, and by 2000 BC they were expanding past
19072-417: The surface. The rotation rate was gradually slowed by magnetic braking , as the Sun's magnetic field interacted with the outflowing solar wind. A vestige of this rapid primordial rotation still survives at the Sun's core, which has been found to be rotating at a rate of once per week; four times the mean surface rotation rate. The Sun consists mainly of the elements hydrogen and helium . At this time in
19221-431: The tachocline picks up heat and expands, thereby reducing its density and allowing it to rise. As a result, an orderly motion of the mass develops into thermal cells that carry most of the heat outward to the Sun's photosphere above. Once the material diffusively and radiatively cools just beneath the photospheric surface, its density increases, and it sinks to the base of the convection zone, where it again picks up heat from
19370-424: The temperature of the corona, at least some of its heat is known to be from magnetic reconnection . The corona is the extended atmosphere of the Sun, which has a volume much larger than the volume enclosed by the Sun's photosphere. A flow of plasma outward from the Sun into interplanetary space is the solar wind . The heliosphere, the tenuous outermost atmosphere of the Sun, is filled with solar wind plasma and
19519-422: The tenuous layers above the photosphere. The photosphere has a particle density of ~10 m (about 0.37% of the particle number per volume of Earth's atmosphere at sea level). The photosphere is not fully ionized—the extent of ionization is about 3%, leaving almost all of the hydrogen in atomic form. The Sun's atmosphere is composed of five layers: the photosphere, the chromosphere , the transition region ,
19668-524: The territories of the former kingdoms of Sumer and Akkad . The Neo-Babylonian Empire , or Chaldea , was Babylonia from the 7th and 6th centuries BC. Under the reign of Nebuchadnezzar II , it conquered Jerusalem . This empire also created the Hanging Gardens of Babylon and the still-surviving Ishtar Gate as architectural embellishments of its capital at Babylon. Akkad was a city and its surrounding region near Babylon. Akkad also became
19817-517: The time period of ancient history, the world population was already exponentially increasing due to the Neolithic Revolution , which was in full progress. While in 10,000 BC, the world population stood at 2 million, it rose to 45 million by 3000 BC. By the Iron Age in 1000 BC, the population had risen to 72 million. By the end of the ancient period in AD 500, the world population is thought to have stood at 209 million. In 10,500 years,
19966-404: The top of the radiative zone and the convective cycle continues. At the photosphere, the temperature has dropped 350-fold to 5,700 K (9,800 °F) and the density to only 0.2 g/m (about 1/10,000 the density of air at sea level, and 1 millionth that of the inner layer of the convective zone). The thermal columns of the convection zone form an imprint on the surface of the Sun giving it
20115-418: The transfer of energy through this zone is by radiation instead of thermal convection. Ions of hydrogen and helium emit photons, which travel only a brief distance before being reabsorbed by other ions. The density drops a hundredfold (from 20 000 kg/m to 200 kg/m ) between 0.25 solar radii and 0.7 radii, the top of the radiative zone. The radiative zone and the convective zone are separated by
20264-568: The use of fire has been dated as early as 1.8 million years ago, a date which is contested, with generally accepted evidence for the controlled use of fire dating to 780,000 years ago. Actual use of hearths first appears 400,000 years ago. Dates for the emergence of Homo sapiens (modern humans) range from 250,000 to 160,000 years ago, with the varying dates being based on DNA studies and fossils respectively. Some 50,000 years ago, Homo sapiens migrated out of Africa . They reached Australia about 45,000 years ago, southwestern Europe about
20413-569: The world population increased by 100 times. Prehistory is the period before written history. Most of our knowledge of that period comes from the work of archaeologists. Prehistory is often known as the Stone Age , and is divided into the Paleolithic (earliest), Mesolithic , and Neolithic . The early human migrations in the Lower Paleolithic saw Homo erectus spread across Eurasia 1.8 million years ago. Evidence for
20562-540: Was Washukanni , whose precise location has not been determined by archaeologists. The Medes and Persians were peoples who had appeared in the Iranian plateau around 1500 BC. Both peoples spoke Indo-European languages and were mostly pastoralists with a tradition of horse archery. The Medes established their own Median Empire by the 6th century BC, having defeated the Neo-Assyrian Empire with
20711-477: Was a city-state that ruled an empire through alliances and trade influence that stretched throughout North Africa and modern Spain . At the height of the city's influence, its empire included most of the western Mediterranean. The empire was in a constant state of struggle with the Roman Republic , which led to a series of conflicts known as the Punic Wars . After the third and final Punic War , Carthage
20860-492: Was an important trading nation in northeastern Africa centered in present-day Eritrea and northern Ethiopia , it existed from approximately AD 100 to 940, growing from the Iron Age proto-Aksumite period around the 4th century BC to achieve prominence by the 1st century AD. The Kingdom of Aksum at its height by the early 6th-century AD extended through much of modern Ethiopia and across the Red Sea to Arabia. The capital city of
21009-445: Was characterized by several migrations into Mainland and Island Southeast Asia from southern China by Austronesian , Austroasiatic , Kra-Dai and Hmong-Mien -speakers. Territorial principalities in both Insular and Mainland Southeast Asia, characterized as "agrarian kingdoms", developed an economy by around 500 BCE based on surplus crop cultivation and moderate coastal trade of domestic natural products. Several states of
21158-541: Was destroyed and then occupied by Roman forces. Nearly all of the territory held by Carthage fell into Roman hands. Ancient Egypt was a long-lived civilisation geographically located in north-eastern Africa. It was concentrated along the middle to lower reaches of the Nile River, reaching its greatest extent during the 2nd millennium BC, which is referred to as the New Kingdom period. It reached broadly from
21307-455: Was developed independent of Chinese or Indian influence. Historians relate these achievements to the presence of organized, centralized and hierarchical communities and a large population. Between 1000 BCE and 100 CE, the Sa Huỳnh culture flourished along the south-central coast of Vietnam . Ceramic jar burial sites that included grave goods have been discovered at various sites along
21456-720: Was developed independently in China by 2000 BC. Pottery developed independently throughout the world, with fired pots appearing first among the Jomon of Japan and in West Africa at Mali . Sometime between 5000 and 4000 BC the potter's wheel was invented. By 3000 BC, the pottery wheel was adapted into wheeled vehicles which could be used to carry loads further and easier than with human or animal power alone. Writing developed separately in five different locations in human history: Mesopotamia, Egypt, India, China, and Mesoamerica. By 3400 BC, "proto-literate" cuneiform spread in
21605-421: Was evolving into Hinduism , which spread throughout Southeast Asia. Siddhartha Gautama , born around 560 BC in northern India, went on to found a new religion based on his ascetic life – Buddhism . This faith also spread throughout Eastern and Southeastern Asia after his death. This period also saw the composition of the epics Ramayana and Mahabharata . The kingdom of Magadha rose to prominence under
21754-524: Was located in the Niger River Valley in the country of Mali and is considered to be among the oldest urbanized centers and the best-known archaeology site in sub-Saharan Africa . This archaeological site is located about 3 kilometers (1.9 miles) away from the modern town and is believed to have been involved in long-distance trade and possibly the domestication of African rice. The site is believed to exceed 33 hectares (82 acres); however, this
21903-512: Was ruled by the Seleucid dynasty . Parthia was an Iranian civilisation situated in the northeastern part of modern Iran. Their power was based on a combination of military power based on heavy cavalry with a decentralised governing structure based on a federated system . The Parthian Empire was led by the Arsacid dynasty , which by around 155 BC under Mithradates I had mostly conquered
22052-682: Was sacked, ending the Hittite Empire . Israel and Judah were related Iron Age kingdoms of the ancient Levant and had existed during the Iron Ages and the Neo-Babylonian, Persian and Hellenistic periods. The name Israel first appears in the stele of the Egyptian pharaoh Merneptah around 1209 BC. This "Israel" was a cultural and probably political entity of the central highlands, well enough established to be perceived by
22201-634: Was the main language of diplomacy in the Near East. Assyria was originally a region on the Upper Tigris , where a small state was created in the 19th century BC. The capital was at Assur , which gave the state its name. Later, as a nation and empire that came to control all of the Fertile Crescent, Egypt and much of Anatolia , the term "Assyria proper" referred to roughly the northern half of Mesopotamia (the southern half being Babylonia), with Nineveh as its capital. The Assyrian kings controlled
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