Free Online Library: Australian Solar Radiation Data Handbook Edition 4.(Book review) by 'Australian Journal of Environmental Education'; Environmental issues Books Book reviews. Browse by Topic. Find books in subject areas that are of interest to you.

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Australian Solar Radiation Data Handbook Edition 4. Compiled by Energy Partners in association with Adelaide Applied Algebra. NSW: Australian and New Zealand Solar Energy Society (ANZSES), 2006. ISBN 0 642 19121 2. Available in hardcopy or CD.

Sorry G Wrong Number Mp3 Song Download. Schools have an increasing interest in the use of sustainable energy as both an educational topic and for improving their own environmental performance. Solar energy is the most abundant sustainable energy source, so access to reliable solar radiation data is imperative. This data is available in Australia in the form of the AUSOLRAD Manual and Software.

It can be purchased from the Australian and New Zealand Solar Energy Society www.anzses.org. Data has been taken from 28 Bureau of Meteorology sites around Australia for typical years. I have been using this resource in my teaching within TAFE and Universities for many years and have found it invaluable. The AUSSOLRAD package consists of a user guide and program that uses the Microsoft.NET framework.

It is easy to install and can import and export data to spreadsheets for example. Microsoft Office Frontpage 2000 Free Download. Data tables in the software include climatic averages such as temperature, humidity and cloud cover, as well as processed solar radiation data for standard orientations (north, south, east and west) and inclinations (horizontal or latitude angle). Processed data includes: * Degree heating and cooling days--used to assess the need for space heating and cooling in buildings.

* Solar irradiance (power in W/[m.sup.2]) for each hour and total irradiation (energy in MJ/[m.sup.2]) over an average day for each month for planes of fixed orientation and inclination in 10 degree increments e.g., average daily irradiation in July falling on a solar collector plane facing 40 East of North and tilted at 20 degrees to the horizontal. * Sun angles (azimuth and altitude) defining the position of the sun in the sky hour by hour. * Solar irradiation that is broken into direct (or beam) and diffuse (or scattered) components. This information is used for sun tracking systems, that is, solar energy systems where the solar collectors move to point perpendicular to the sun's rays throughout the day. * Solar heat gain through windows of any orientation and tilt with simple horizontal shades. There is also a calculator that allows estimation of average solar radiation on walls or heat gain through windows of any orientation and tilt. There are many uses for this data and the table below summarises some of these.

Some examples of how I have used the data in class include: * Simple exercises in comparing the effect of orientation on solar gain in buildings and the need for appropriate shading of windows, summer to winter. * Comparing the effect of changing the tilt angle of the collectors from summer to winter on solar system performance. * Estimating the output of fixed photovoltaic systems for power generation into the electricity grid. Many schools now have their own such systems so estimates can be compared to actual measured data.

Example of Data Use Solar irradiance (power) and To examine how the solar resource irradiation (energy) for each hour varies over the day and year. On any plane. Total irradiation (energy) for an To estimate the average average day each month for fixed performance of solar energy planes of orientation or systems such as photovoltaic inclination in 10 degree (electric) systems and solar water increments. Heaters set at fixed orientations and tilts. Total irradiation and the beam The total irradiation is used to and diffuse components for sun estimate performance of tracking systems.

Photovoltaic tracking systems and to compare their performance with fixed collectors. Beam components are used for concentrating solar collectors that produce high temperature steam for power generation or process heat. Solar heat gain through windows. Allows estimation of the effects of window placement and shading on space heating and cooling of buildings. Who is this data applicable to? Science, maths and environmental educators should be able to make good use of this package with their classes, for example, in assessing and using solar radiation data for their region or to compare regions across Australia. Trevor Berrill Environmental Educator and Renewable Energy Systems Consultant.

Sun with and as seen in with solar filter. Main article: Solar deities play a major role in many world religions and mythologies. The ancient believed that the sun was, the god of justice and twin brother of, the, who was identified as the planet. Later, Utu was identified with the god. Utu was regarded as a helper-deity, who aided those in distress, and, in, he is usually portrayed with a long beard and clutching a, which represented his role as the dispenser of justice. From at least the of, the Sun was worshipped as the, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the period, the Sun became identified with the, whose spherical ball of dung was identified with the Sun.

In the form of the Sun disc, the Sun had a brief resurgence during the when it again became the preeminent, if not only, divinity for the. In, the sun was personified as the goddess. Derivatives of this goddess in include the,,,, and Solntse. In, the sun deity was the male god, but traces of an earlier female solar deity are preserved in.

In later times, Helios was with. In the, mentions the 'Sun of Righteousness' (sometimes translated as the 'Sun of Justice'), which some have interpreted as a reference to the (). In ancient Roman culture, was the day of the Sun god. It was adopted as the day by Christians who did not have a Jewish background. The symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions.

In paganism, the Sun was a source of life, giving warmth and illumination to mankind. It was the center of a popular cult among Romans, who would stand at dawn to catch the first rays of sunshine as they prayed. The celebration of the (which influenced Christmas) was part of the Roman cult of the unconquered Sun (). Christian churches were built with an orientation so that the congregation faced toward the sunrise in the East., the god of the sun, was usually depicted holding arrows and a shield and was closely associated with the practice of. The sun goddess is the most important deity in the religion, and she is believed to be the direct ancestor of all. Characteristics The Sun is a that comprises about 99.86% of the mass of the Solar System. The Sun has an of +4.83, estimated to be brighter than about 85% of the stars in the, most of which are.

The Sun is a, or heavy-element-rich, star. The formation of the Sun may have been triggered by shockwaves from one or more nearby. This is suggested by a high of heavy elements in the Solar System, such as and, relative to the abundances of these elements in so-called, heavy-element-poor, stars. The heavy elements could most plausibly have been produced by nuclear reactions during a supernova, or by through within a massive second-generation star.

The Sun is by far the brightest object in the Earth's sky, with an of −26.74. This is about 13 billion times brighter than the next brightest star,, which has an apparent magnitude of −1.46. The mean distance of the Sun's center to Earth's center is approximately 1 (about 150,000,000 km; 93,000,000 mi), though the distance varies as Earth moves from in January to in July. At this average distance, light travels from the Sun's horizon to Earth's horizon in about 8 minutes and 19 seconds, while light from the closest points of the Sun and Earth takes about two seconds less. The energy of this supports almost all life on Earth by, and drives and weather. The Sun does not have a definite boundary, but its density decreases exponentially with increasing height above the.

For the purpose of measurement, however, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun. By this measure, the Sun is a near-perfect sphere with an estimated at about 9 millionths, which means that its polar diameter differs from its equatorial diameter by only 10 kilometres (6.2 mi). The tidal effect of the planets is weak and does not significantly affect the shape of the Sun.

The Sun rotates faster at its than at its. This is caused by due to heat transport and the due to the Sun's rotation. In a frame of reference defined by the stars, the rotational period is approximately 25.6 days at the equator and 33.5 days at the poles. Viewed from Earth as it orbits the Sun, the apparent rotational period of the Sun at its equator is about 28 days. Main article: The 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 000000000♠1,368 W/m 2 (watts per square meter) at a distance of one (AU) from the Sun (that is, on or near Earth). Sunlight on the surface of Earth is by Earth's atmosphere, so that less power arrives at the surface (closer to 000000000♠1,000 W/m 2) in clear conditions when the Sun is near the. 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 in particular filters out over 70% of solar ultraviolet, especially at the shorter wavelengths.

Solar ionizes Earth's dayside upper atmosphere, creating the electrically conducting. The Sun's color is white, with a color-space index near (0.3, 0.3), when viewed from space or when the Sun is high in the sky. When measuring all the photons emitted, the Sun is actually emitting more photons in the green portion of the spectrum than any other. When the Sun is low in the sky, renders the Sun yellow, red, orange, or magenta. Despite its typical whiteness, most people mentally picture the Sun as yellow; the reasons for this are the subject of debate. The Sun is a star, with G2 indicating its of approximately 5,778 K (5,505 °C, 9,941 °F), and V that it, like most stars, is a star.

The average of the Sun is about 1.88, but as viewed through Earth's atmosphere, this is lowered to about 1.44 Gcd/m 2. However, the luminance is not constant across the disk of the Sun (). See also: The Sun is composed primarily of the and; they account for 74.9% and 23.8% of the mass of the Sun in the photosphere, respectively. All heavier elements, called 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 inherited its chemical composition from the out of which it formed. The hydrogen and helium in the Sun were produced by, and the heavier elements were produced by in generations of stars that completed their and returned their material to the interstellar medium before the formation of the Sun. The chemical composition of the photosphere is normally considered representative of the composition of the primordial Solar System. However, since the Sun formed, some of the helium and heavy elements have gravitationally settled from the photosphere. Therefore, in today's photosphere the helium fraction is reduced, and the is only 84% of what it was in the phase (before nuclear fusion in the core started). The protostellar Sun's composition is believed to have been 71.1% hydrogen, 27.4% helium, and 1.5% heavier elements.

Today, nuclear fusion in the Sun's core has modified the composition by converting hydrogen into helium, so the innermost portion of the Sun is now roughly 60% helium, with the abundance of heavier elements unchanged. Because heat is transferred from the Sun's core by radiation rather than by convection (see below), none of the fusion products from the core have risen to the photosphere. The reactive core zone of 'hydrogen burning', where hydrogen is converted into helium, is starting to surround an inner core of 'helium ash'. This development will continue and will eventually cause the Sun to leave the, to become a. The solar heavy-element abundances described above are typically measured both using of the Sun's photosphere and by measuring abundances in 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 settling of heavy elements. The two methods generally agree well.

Singly ionized iron-group elements In the 1970s, much research focused on the abundances of elements in the Sun. Although significant research was done, until 1978 it was difficult to determine the abundances of some iron-group elements (e.g. And ) via because of their. The first largely complete set of of singly ionized iron-group elements were made available in the 1960s, and these were subsequently improved.

In 1978, the abundances of singly ionized elements of the iron group were derived. Isotopic composition Various authors have considered the existence of a gradient in the compositions of solar and planetary, e.g. Correlations between isotopic compositions of and in the Sun and on the planets. Prior to 1983, it was thought that the whole Sun has the same composition as the solar atmosphere. In 1983, it was claimed that it was in the Sun itself that caused the isotopic-composition relationship between the planetary and solar-wind-implanted noble gases.

Structure and energy production Core. The structure of the Sun The of the Sun extends from the center to about 20–25% of the solar radius. It has a density of up to 000000000♠150 g/cm 3 (about 150 times the density of water) and a temperature of close to 15.7 million (K). By contrast, the Sun's surface temperature is approximately 5,800 K. Recent analysis of mission data favors a faster rotation rate in the core than in the radiative zone above.

Through most of the Sun's life, energy has been produced by in the core region through a series of steps called the; this process converts into. Only 0.8% of the energy generated in the Sun comes from the, though this proportion is expected to increase as the Sun becomes older. The core is the only region in the Sun that produces an appreciable amount of through fusion; 99% of the power is generated within 24% of the Sun's radius, and by 30% of the radius, fusion has stopped nearly entirely. The remainder of the Sun is heated by this energy as it is transferred outwards through many successive layers, finally to the solar photosphere where it escapes into space as sunlight or the of particles. The occurs around 999999999♠9.2 ×10 37 times each second in the core, converting about 3.7 ×10 38 protons into (helium nuclei) every second (out of a total of ~8.9 ×10 56 free protons in the Sun), or about 6.2 ×10 11 kg/s. Fusing four free (hydrogen nuclei) into a single (helium nucleus) releases around 0.7% of the fused mass as energy, so the Sun releases energy at the mass–energy conversion rate of 4.26 million metric tons per second (which requires 600 metric megatons of hydrogen ), for 384.6 ( 000000000♠3.846 ×10 26 W), or 9.192 ×10 10 of per second. Theoretical models of the Sun's interior indicate a power density of approximately 276.5 W/m 3, a value that more nearly approximates that of reptile metabolism or a compost pile than of a thermonuclear bomb.

The fusion rate in the core is in a self-correcting equilibrium: a slightly higher rate of fusion would cause the core to heat up more and slightly against the weight of the outer layers, reducing the density and hence the fusion rate and correcting the; 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. Radiative zone. Main article: From the core out to about 0.7 solar radii, 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 is less than the value of the and hence cannot drive convection, which explains why the transfer of energy through this zone is by instead of thermal. Of and emit, which travel only a brief distance before being reabsorbed by other ions. The density drops a hundredfold (from 20 g/cm 3 to 0.2 g/cm 3) from 0.25 solar radii to the 0.7 radii, the top of the radiative zone. Main article: The Sun's convection zone extends from 0.7 solar radii (200,000 km) to near the surface. In this layer, the solar plasma is not dense enough 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 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 that carry the majority 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 the top of the radiative zone and the convective cycle continues.

At the photosphere, the temperature has dropped to 5,700 K and the density to only 0.2 g/m 3 (about 1/6,000 the density of air at sea level). The thermal columns of the convection zone form an imprint on the surface of the Sun giving it a granular appearance called the at the smallest scale and 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 and take the shape of hexagonal prisms. Main article: The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes to visible light.

Above the photosphere visible sunlight is free to propagate into space, and almost all of its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of, which absorb visible light easily. Conversely, the visible light we see is produced as electrons react with atoms to produce H − ions. The photosphere 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. The spectrum of sunlight has approximately the spectrum of a radiating at about 6,000, interspersed with atomic from the tenuous layers above the photosphere. The photosphere has a particle density of ~10 23 m −3 (about 0.37% of the particle number per volume of 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. During early studies of the of the photosphere, some absorption lines were found that did not correspond to any then known on Earth.

In 1868, hypothesized that these absorption lines were caused by a new element that he dubbed, after the Greek Sun god. Twenty-five years later, helium was isolated on Earth. During a total, the solar can be seen with the naked eye, during the brief period of totality. During a total, when the disk of the Sun is covered by that of the Moon, parts of the Sun's surrounding atmosphere can be seen. It is composed of four distinct parts: the, the, the and the. The coolest layer of the Sun is a temperature minimum region extending to about 000000000♠500 km above the photosphere, and has a temperature of about 000000000♠4,100.

This part of the Sun is cool enough to allow the existence of simple molecules such as and water, which can be detected via their absorption spectra. The chromosphere, transition region, and corona are much hotter than the surface of the Sun. The reason is not well understood, but evidence suggests that may have enough energy to heat the corona. Above the temperature minimum layer is a layer about 000000000♠2,000 km thick, dominated by a spectrum of emission and absorption lines. It is called the chromosphere from the Greek root chroma, meaning color, because the chromosphere is visible as a colored flash at the beginning and end of total.

The temperature of the chromosphere increases gradually with altitude, ranging up to around 000000000♠20,000 K near the top. In the upper part of the chromosphere becomes partially. See also: High-energy 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 a few millimeters.

Re-emission happens in a random direction and usually at a 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 the, which account for about 2% of the total energy production of 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.

Neutrinos are also released by the fusion reactions in the core, but, unlike photons, they rarely interact with matter, so almost all are able to escape the Sun immediately. For many years measurements of the number of neutrinos produced in the Sun were by a factor of 3.

This discrepancy was resolved in 2001 through the discovery of the effects of: the Sun emits the number of neutrinos predicted by the, but neutrino detectors were missing ​ 2⁄ 3 of them because the neutrinos had changed by the time they were detected. Magnetism and activity Magnetic field. The extends to the outer reaches of the Solar System, and results from the influence of the Sun's rotating magnetic field on the in the.

The Sun has a that varies across the surface of the Sun. Its polar field is 1–2 (0.0001–0.0002 ), whereas the field is typically 3,000 gauss (0.3 T) in features on the Sun called and 10–100 gauss (0.001–0.01 T) in. The magnetic field also varies in time and location. The quasi-periodic 11-year is the most prominent variation in which the number and size of sunspots waxes and wanes. Sunspots are visible as dark patches on the Sun's, and correspond to concentrations of magnetic field where the of heat is inhibited from the solar interior to the surface. As a result, sunspots are slightly cooler than the surrounding photosphere, and, so, they appear dark. At a typical, few sunspots are visible, and occasionally none can be seen at all.

Those that do appear are at high solar latitudes. As the solar cycle progresses towards its, sunspots tend form closer to the solar equator, a phenomenon known as.

The largest sunspots can be tens of thousands of kilometers across. An 11-year sunspot cycle is half of a 22-year –Leighton cycle, which corresponds to an oscillatory exchange of energy between solar magnetic fields. At, the external poloidal dipolar magnetic field is near its dynamo-cycle minimum strength, but an internal 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 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, a phenomenon known as the Hale cycle. 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, 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 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 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. In an approximation known as ideal, plasma particles only move along the magnetic field lines. As 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 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 structure called the. The interplanetary magnetic field is much stronger than the dipole component of the solar magnetic field. The Sun's dipole magnetic field of 50–400 (at the photosphere) reduces with the inverse-cube of the distance to about 0.1 nT at the distance of Earth.

However, according to spacecraft observations the interplanetary field at Earth's location is around 5 nT, about a hundred times greater. The difference is due to magnetic fields generated by electrical currents in the plasma surrounding the Sun.

Variation in activity. Measurements from 2005 of solar cycle variation during the last 30 years The Sun's magnetic field leads to many effects that are collectively called. And tend to occur at sunspot groups.

Slowly changing high-speed streams of are emitted from at the photospheric surface. Both coronal-mass ejections and high-speed streams of solar wind carry plasma and outward into the Solar System.

The effects of solar activity on Earth include at moderate to high latitudes and the disruption of radio communications and. Solar activity is thought to have played a large role in the. With solar-cycle modulation of sunspot number comes a corresponding modulation of conditions, including those surrounding Earth where technological systems can be affected.

Long-term change 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. For example, in the 17th century, the solar cycle appeared to have stopped entirely for several decades; few sunspots were observed during a period known as the.

This coincided in time with the era of the, when Europe experienced unusually cold temperatures. Earlier extended minima have been discovered through analysis of and appear to have coincided with lower-than-average global temperatures. A recent theory claims that there are magnetic instabilities in the core of the Sun that cause fluctuations with periods of either 41,000 or 100,000 years. These could provide a better explanation of the than the.

Main articles: and The Sun today is roughly halfway through the most stable part of its life. It has not changed dramatically for over four billion years, and will remain fairly stable for more than five billion more.

However, after hydrogen fusion in its core has stopped, the Sun will undergo severe changes, both internally and externally. Formation The Sun formed about 4.6 billion years ago from the collapse of part of a giant that consisted mostly of hydrogen and helium and that probably gave birth to many other stars. This age is estimated using of and through. The result is consistent with the of the oldest Solar System material, at 4.567 billion years ago.

Studies of ancient reveal traces of stable daughter nuclei of short-lived isotopes, such as, that form only in exploding, short-lived stars. This indicates that one or more supernovae must have occurred near the location where the Sun formed. A from a nearby supernova would have triggered the formation of the Sun by compressing the matter within the molecular cloud and causing certain regions to collapse under their own gravity. As one fragment of the cloud collapsed it also began to rotate because of and heat up with the increasing pressure.

Much of the mass became concentrated in the center, whereas the rest flattened out into a disk that would become the planets and other Solar System bodies. Gravity and pressure within the core of the cloud generated a lot of heat as it accreted more matter from the surrounding disk, eventually triggering. Thus, the Sun was born.

Main sequence. Evolution of the Sun's, and compared to the present Sun. After Ribas (2010) The Sun is about halfway through its stage, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than four million of matter are converted into energy within the Sun's core, producing and. At this rate, the Sun has so far converted around 100 times the mass of Earth into energy, about 0.03% of the total mass of the Sun.

The Sun will spend a total of approximately 10 years as a main-sequence star. The Sun is gradually becoming hotter during its time on the main sequence, because the helium atoms in the core occupy less volume than the that were fused. The core is therefore shrinking, allowing the outer layers of the Sun to move closer to the centre and experience a stronger gravitational force, according to the. This stronger force increases the pressure on the core, which is resisted by a gradual increase in the rate at which fusion occurs. This process speeds up as the core gradually becomes denser.

It is estimated that the Sun has become 30% brighter in the last 4.5 billion years. At present, it is increasing in brightness by about 1% every 100 million years. After core hydrogen exhaustion. The size of the current Sun (now in the ) compared to its estimated size during its red-giant phase in the future The Sun does not have enough mass to explode as a. Instead it will exit the in approximately 5 billion years and start to turn into a. As a red giant, the Sun will grow so large that it will engulf Mercury, Venus, and probably Earth. Even before it becomes a red giant, the luminosity of the Sun will have nearly doubled, and Earth will receive as much sunlight as Venus receives today.

Once the core hydrogen is exhausted in 5.4 billion years, the Sun will expand into a phase and slowly double in size over about half a billion years. It will then expand more rapidly over about half a billion years until it is over two hundred times larger than today and a couple of thousand times more luminous. This then starts the phase where the Sun will spend around a billion years and lose around a third of its mass. Evolution of a Sun-like star.

The track of a one solar mass star on the is shown from the main sequence to the post-asymptotic-giant-branch stage. After the red-giant branch the Sun has approximately 120 million years of active life left, but much happens. First, the core, full of helium ignites violently in the, where it is estimated that 6% of the core, itself 40% of the Sun's mass, will be converted into carbon within a matter of minutes through the. The Sun then shrinks to around 10 times its current size and 50 times the luminosity, with a temperature a little lower than today. It will then have reached the or, but a star of the Sun's mass does not evolve blueward along the horizontal branch. Instead, it just becomes moderately larger and more luminous over about 100 million years as it continues to burn helium in the core. When the helium is exhausted, the Sun will repeat the expansion it followed when the hydrogen in the core was exhausted, except that this time it all happens faster, and the Sun becomes larger and more luminous.

This is the phase, and the Sun is alternately burning hydrogen in a shell or helium in a deeper shell. After about 20 million years on the early asymptotic giant branch, the Sun becomes increasingly unstable, with rapid mass loss and that increase the size and luminosity for a few hundred years every 100,000 years or so. The thermal pulses become larger each time, with the later pulses pushing the luminosity to as much as 5,000 times the current level and the radius to over 1 AU. According to a 2008 model, Earth's orbit is shrinking due to (and, eventually, drag from the lower ), so that it will be engulfed by the Sun near the tip of the red giant branch phase, 1 and 3.8 million years after Mercury and Venus have respectively suffered the same fate. Models vary depending on the rate and timing of mass loss. Models that have higher mass loss on the red-giant branch produce smaller, less luminous stars at the tip of the asymptotic giant branch, perhaps only 2,000 times the luminosity and less than 200 times the radius.

For the Sun, four thermal pulses are predicted before it completely loses its outer envelope and starts to make a. By the end of that phase – lasting approximately 500,000 years – the Sun will only have about half of its current mass. The post-asymptotic-giant-branch evolution is even faster. The luminosity stays approximately constant as the temperature increases, with the ejected half of the Sun's mass becoming ionised into a as the exposed core reaches 30,000 K.

The final naked core, a, will have a temperature of over 100,000 K, and contain an estimated 54.05% of the Sun's present day mass. The planetary nebula will disperse in about 10,000 years, but the white dwarf will survive for trillions of years before fading to a hypothetical. Motion and location Orbit in Milky Way. Illustration of the Milky Way, showing the location of the Sun The Sun lies close to the inner rim of the 's, in the or the, at a distance of 7.5–8.5 (25,000–28,000 light-years) from the. The Sun is contained within the, a space of rarefied hot gas, possibly produced by the supernova remnant, or multiple supernovae in subgroup B1 of the Pleiades moving group. The distance between the local arm and the next arm out, the, is about 6,500 light-years.

The Sun, and thus the Solar System, is found in what scientists call the. The Apex of the Sun's Way, or the, is the direction that the Sun travels relative to other nearby stars. This motion is towards a point in the constellation, near the star. Of the 50 within 17 light-years from Earth (the closest being the red dwarf at approximately 4.2 light-years), the Sun ranks fourth in mass. The Sun orbits the center of the Milky Way, and it is presently moving in the direction of the constellation of. The Sun's orbit around the Milky Way is roughly elliptical with orbital perturbations due to the non-uniform mass distribution in Milky Way, such as that in and between the galactic spiral arms. In addition, the Sun oscillates up and down relative to the galactic plane approximately 2.7 times per orbit.

It has been argued that the Sun's passage through the higher density spiral arms often coincides with on Earth, perhaps due to increased. It takes the Solar System about 225–250 million years to complete one orbit through the Milky Way (a ), so it is thought to have completed 20–25 orbits during the lifetime of the Sun. The of the Solar System about the center of the Milky Way is approximately 251 km/s (156 mi/s).

At this speed, it takes around 1,190 years for the Solar System to travel a distance of 1 light-year, or 7 days to travel 1. The Milky Way is moving with respect to the (CMB) in the direction of the constellation with a speed of 550 km/s, and the Sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of.

Theoretical problems. Main article: Theoretical models of the Sun's development suggest that 3.8 to 2.5 billion years ago, during the, the Sun was only about 75% as bright as it is today.

Such a weak star would not have been able to sustain liquid water on Earth's surface, and thus life should not have been able to develop. However, the geological record demonstrates that Earth has remained at a fairly constant temperature throughout its history, and that the young Earth was somewhat warmer than it is today. One theory among scientists is that the atmosphere of the young Earth contained much larger quantities of (such as, ) than are present today, which trapped enough heat to compensate for the smaller amount of reaching it. However, examination of Archaean sediments appears inconsistent with the hypothesis of high greenhouse concentrations.

Instead, the moderate temperature range may be explained by a lower surface brought about by less continental area and the 'lack of biologically induced cloud condensation nuclei'. This would have led to increased absorption of solar energy, thereby compensating for the lower solar output.

History of observation The enormous effect of the Sun on Earth has been recognized since, and the Sun has been as a. Early understanding. See also: The Sun has been an object of veneration in many cultures throughout human history. Humanity's most fundamental understanding of the Sun is as the luminous disk in the, whose presence above the creates day and whose absence causes night. In many prehistoric and ancient cultures, the Sun was thought to be a or other entity.

Was central to civilizations such as the, the of South America and the of what is now. In religions such as, the Sun is still considered a god. Many ancient monuments were constructed with solar phenomena in mind; for example, stone accurately mark the summer or winter (some of the most prominent megaliths are located in,;, Malta and at, England);, a prehistoric human-built mount in Ireland, was designed to detect the winter solstice; the pyramid of at in Mexico is designed to cast shadows in the shape of serpents climbing the at the vernal and autumnal. The Egyptians portrayed the god as being carried across the sky in a solar barque, accompanied by lesser gods, and to the Greeks, he was, carried by a chariot drawn by fiery horses.

From the reign of in the the Sun's birthday was a holiday celebrated as (literally 'Unconquered Sun') soon after the winter solstice, which may have been an antecedent to Christmas. Regarding the, the Sun appears from Earth to revolve once a year along the through the, and so Greek astronomers categorized it as one of the seven (Greek planetes, 'wanderer'); the naming of the after the seven planets dates to the. Development of scientific understanding In the early first millennium BC, observed that the Sun's motion along the ecliptic is not uniform, though they did not know why; it is today known that this is due to the movement of in an around the Sun, with Earth moving faster when it is nearer to the Sun at and moving slower when it is farther away. One of the first people to offer a scientific or philosophical explanation for the Sun was the. He reasoned that it was not the of, but instead a giant flaming ball of metal even larger than the land of the and that the reflected the light of the Sun.

For teaching this, he was imprisoned by the authorities and, though he was later released through the intervention of. Estimated the distance between Earth and the Sun in the 3rd century BC as 'of stadia 400 and 80000', the translation of which is ambiguous, implying either 4,080,000 (755,000 km) or 804,000,000 stadia (148 to 153 million kilometers or 0.99 to 1.02 AU); the latter value is correct to within a few percent. In the 1st century AD, estimated the distance as 1,210 times, approximately 7.71 million kilometers (0.0515 AU). The theory that the Sun is the center around which the planets orbit was first proposed by the ancient Greek in the 3rd century BC, and later adopted by (see ). This view was developed in a more detailed of a heliocentric system in the 16th century.

Observations of sunspots were recorded during the (206 BC–AD 220) by, who maintained records of these observations for centuries. Also provided a description of sunspots in the 12th century.

The invention of the in the early 17th century permitted detailed observations of by, and other astronomers. Galileo posited that sunspots were on the surface of the Sun rather than small objects passing between Earth and the Sun. Include ' discovery that the direction of the Sun's (the place in the Sun's orbit against the fixed stars where it seems to be moving slowest) is changing. (In modern heliocentric terms, this is caused by a gradual motion of the aphelion of the Earth's orbit). Observed more than 10,000 entries for the Sun's position for many years using a large. Sol, the Sun, from a 1550 edition of 's Liber astronomiae. From an observation of a in 1032, the Persian astronomer and polymath concluded that Venus is closer to Earth than the Sun.

In 1672 and determined the distance to and were thereby able to calculate the distance to the Sun. In 1666, observed the Sun's light using a, and showed that it is made up of light of many colors. In 1800, discovered radiation beyond the red part of the solar spectrum. The 19th century saw advancement in spectroscopic studies of the Sun; recorded more than 600 in the spectrum, the strongest of which are still often referred to as. In the early years of the modern scientific era, the source of the Sun's energy was a significant puzzle. Suggested that the Sun is a gradually cooling liquid body that is radiating an internal store of heat.

Kelvin and then proposed a mechanism to explain the energy output, but the resulting age estimate was only 20 million years, well short of the time span of at least 300 million years suggested by some geological discoveries of that time. In 1890, who discovered helium in the solar spectrum, proposed a meteoritic hypothesis for the formation and evolution of the Sun.

Not until 1904 was a documented solution offered. Suggested that the Sun's output could be maintained by an internal source of heat, and suggested as the source. However, it would be who would provide the essential clue to the source of the Sun's energy output with his relation E = mc 2.

In 1920, Sir proposed that the pressures and temperatures at the core of the Sun could produce a nuclear fusion reaction that merged hydrogen (protons) into helium nuclei, resulting in a production of energy from the net change in mass. The preponderance of hydrogen in the Sun was confirmed in 1925 by using the theory developed by, an Indian physicist. The theoretical concept of fusion was developed in the 1930s by the astrophysicists and. Hans Bethe calculated the details of the two main energy-producing nuclear reactions that power the Sun.

In 1957,,, and showed that most of the elements in the universe have been by nuclear reactions inside stars, some like the Sun. Solar space missions. A lunar transit of the Sun captured during calibration of STEREO B's ultraviolet imaging cameras The first satellites designed to observe the Sun were 's 5, 6, 7, 8 and 9, which were launched between 1959 and 1968. These probes orbited the Sun at a distance similar to that of Earth, and made the first detailed measurements of the solar wind and the solar magnetic field.

Operated for a particularly long time, transmitting data until May 1983. In the 1970s, two spacecraft and the provided scientists with significant new data on solar wind and the solar corona.

The Helios 1 and 2 probes were U.S.–German collaborations that studied the solar wind from an orbit carrying the spacecraft inside 's orbit. The Skylab space station, launched by NASA in 1973, included a solar module called the Apollo Telescope Mount that was operated by astronauts resident on the station. Skylab made the first time-resolved observations of the solar transition region and of ultraviolet emissions from the solar corona. Discoveries included the first observations of, then called 'coronal transients', and of, now known to be intimately associated with the.

In 1980, the was launched. This spacecraft was designed to observe, and radiation from during a time of high solar activity and. Just a few months after launch, however, an electronics failure caused the probe to go into standby mode, and it spent the next three years in this inactive state. In 1984 mission retrieved the satellite and repaired its electronics before re-releasing it into orbit. The Solar Maximum Mission subsequently acquired thousands of images of the solar corona before Earth's atmosphere in June 1989. Launched in 1991, Japan's ( Sunbeam) satellite observed solar flares at X-ray wavelengths.

Mission data allowed scientists to identify several different types of flares, and demonstrated that the corona away from regions of peak activity was much more dynamic and active than had previously been supposed. Yohkoh observed an entire solar cycle but went into standby mode when an in 2001 caused it to lose its lock on the Sun. It was destroyed by atmospheric re-entry in 2005. One of the most important solar missions to date has been the, jointly built by the and and launched on 2 December 1995. Originally intended to serve a two-year mission, a mission extension through 2012 was approved in October 2009. It has proven so useful that a follow-on mission, the (SDO), was launched in February 2010. Situated at the between Earth and the Sun (at which the gravitational pull from both is equal), SOHO has provided a constant view of the Sun at many wavelengths since its launch.

Besides its direct solar observation, SOHO has enabled the discovery of a large number of, mostly tiny that incinerate as they pass the Sun. A solar prominence erupts in August 2012, as captured by SDO All these satellites have observed the Sun from the plane of the ecliptic, and so have only observed its equatorial regions in detail. The was launched in 1990 to study the Sun's polar regions.

It first travelled to, to 'slingshot' into an orbit that would take it far above the plane of the ecliptic. Once Ulysses was in its scheduled orbit, it began observing the solar wind and magnetic field strength at high solar latitudes, finding that the solar wind from high latitudes was moving at about 750 km/s, which was slower than expected, and that there were large magnetic waves emerging from high latitudes that scattered galactic. Elemental abundances in the photosphere are well known from studies, but the composition of the interior of the Sun is more poorly understood. A sample return mission,, was designed to allow astronomers to directly measure the composition of solar material. The (STEREO) mission was launched in October 2006. Two identical spacecraft were launched into orbits that cause them to (respectively) pull further ahead of and fall gradually behind Earth. This enables imaging of the Sun and solar phenomena, such as.

The has scheduled the launch of a 100 kg satellite named for 2017–18. Its main instrument will be a for studying the dynamics of the Solar corona. Observation and effects. The Sun, as seen from low Earth orbit overlooking the. This sunlight is not filtered by the lower atmosphere, which blocks much of the solar spectrum The brightness of the Sun can cause pain from looking at it with the; however, doing so for brief periods is not hazardous for normal non-dilated eyes.

Looking directly at the Sun causes visual artifacts and temporary partial blindness. It also delivers about 4 milliwatts of sunlight to the retina, slightly heating it and potentially causing damage in eyes that cannot respond properly to the brightness. Exposure gradually yellows the lens of the eye over a period of years, and is thought to contribute to the formation of, but this depends on general exposure to solar UV, and not whether one looks directly at the Sun. Long-duration viewing of the direct Sun with the naked eye can begin to cause UV-induced, sunburn-like lesions on the retina after about 100 seconds, particularly under conditions where the UV light from the Sun is intense and well focused; conditions are worsened by young eyes or new lens implants (which admit more UV than aging natural eyes), Sun angles near the zenith, and observing locations at high altitude. Viewing the Sun through light-concentrating such as may result in permanent damage to the retina without an appropriate filter that blocks UV and substantially dims the sunlight. When using an attenuating filter to view the Sun, the viewer is cautioned to use a filter specifically designed for that use.

Some improvised filters that pass UV or rays, can actually harm the eye at high brightness levels., also called Solar Diagonals, are effective and inexpensive for small telescopes. The sunlight that is destined for the eyepiece is reflected from an unsilvered surface of a piece of glass.

Only a very small fraction of the incident light is reflected. The rest passes through the glass and leaves the instrument. If the glass breaks because of the heat, no light at all is reflected, making the device fail-safe. Simple filters made of darkened glass allow the full intensity of sunlight to pass through if they break, endangering the observer's eyesight. Unfiltered binoculars can deliver hundreds of times as much energy as using the naked eye, possibly causing immediate damage. It is claimed that even brief glances at the midday Sun through an unfiltered telescope can cause permanent damage. With Partial are hazardous to view because the eye's is not adapted to the unusually high visual contrast: the pupil dilates according to the total amount of light in the field of view, not by the brightest object in the field.

During partial eclipses most sunlight is blocked by the passing in front of the Sun, but the uncovered parts of the photosphere have the same as during a normal day. In the overall gloom, the pupil expands from ~2 mm to ~6 mm, and each retinal cell exposed to the solar image receives up to ten times more light than it would looking at the non-eclipsed Sun. This can damage or kill those cells, resulting in small permanent blind spots for the viewer. The hazard is insidious for inexperienced observers and for children, because there is no perception of pain: it is not immediately obvious that one's vision is being destroyed.

A sunrise During and, sunlight is attenuated because of and from a particularly long passage through Earth's atmosphere, and the Sun is sometimes faint enough to be viewed comfortably with the naked eye or safely with optics (provided there is no risk of bright sunlight suddenly appearing through a break between clouds). Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation. An, known as a, can sometimes be seen shortly after sunset or before sunrise. The flash is caused by light from the Sun just below the horizon being (usually through a ) towards the observer. Light of shorter wavelengths (violet, blue, green) is bent more than that of longer wavelengths (yellow, orange, red) but the violet and blue light is more, leaving light that is perceived as green.

Light from the Sun has properties and can be used to sanitize tools and water. It also causes, and has other biological effects such as the production of and. Ultraviolet light is strongly attenuated by Earth's, so that the amount of UV varies greatly with and has been partially responsible for many biological adaptations, including variations in in different regions of the globe. Planetary system. • ^ All numbers in this article are short scale.

One billion is 10 9, or 1,000,000,000. • In, the term heavy elements (or metals) refers to all except hydrogen and helium. • live so deep under the sea that they have no access to sunlight. Bacteria instead use sulfur compounds as an energy source, via. • 1.88 Gcd/m 2 is calculated from the solar illuminance of 000000000♠128 000 lux (see ) times the square of the distance to the center of the Sun, divided by the cross sectional area of the Sun. 1.44 Gcd/m 2 is calculated using 000000000♠98 000 lux. • A 50 kg adult human has a volume of about 0.05 m 3, which corresponds to 13.8 watts, at the volumetric power of the solar center.

This is 285 kcal/day, about 10% of the actual average caloric intake and output for humans in non-stressful conditions. • Earth's atmosphere near sea level has a particle density of about 2 ×10 25 m −3.