Sun

Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation. He died on the 8th of July 1827, and was carried to his grave by sea on a flotilla of over 50 sailboats. During sunrise and sunset, sunlight is attenuated by a particularly long passage through Earth's atmosphere, and the direct Sun is sometimes faint enough to be viewed directly without discomfort or safely with binoculars. He subsequently defeated eleven of the officers, one by one, leaving the last and youngest alive "to tell the tale". Viewing the partially eclipsed Sun with the naked eye can cause permanent localized damage to the retina, resulting in small, permanent blind spots for the viewer.^[20] This is an especially insidious hazard for inexperienced observers and for children, because there is no immediate perception of pain and it is tempting to stare at the spectacle of the eclipsing Sun, compounding any damage. In 1817, he fought against twelve Prussian officers with a cue stick because they had insulted an old man in a bar; he managed to hold them long enough to challenge them all to duels. Each retinal cell that is exposed to the partially-eclipsed solar image thus receives about ten times as much light as it would looking at the normal, non-eclipsed Sun. After the war, he returned to Saint-Malo, rich and with the title of baron, and became a merchant ship-owner, establishing business with Terre-Neuve, the Caribbean, Africa and the Indian Ocean.

In the dim overall light, the pupil tends to dilate from about 2 mm to perhaps 6 mm diameter, increasing the eye's collecting area by a factor of nearly 10. However, he took no part in the Hundred Days as a chief of Legion. During partial eclipses, most sunlight is blocked by the Moon passing directly in front of the Sun, but the uncovered parts of the photosphere have the same surface brightness as during a normal day. In January 1814, Surcouf was made a colonel in the National Guard of Saint-Malo. The pupil is controlled by the total amount of light in the visual field, not by the brightest object in the field. Surcouf was received by Napoleon and made Baron d'Empire, and his possessions were returned to him. During partial eclipses of the Sun, another hazardous condition exists because of the way the eye responds to bright light. On the 4th of February 1809, Le Charles arrived in France with a 8-million franc cargo.

Even brief glances at the midday Sun through unfiltered binoculars can cause permanent blindness.^[19]. She would be re-taken two years later by the frigate Bellone, under captain Duperré. Viewing the Sun through unfiltered 7x50 mm binoculars can deliver as much as 2.5 watts of sunlight into each eye, over 300 times more power than naked eye viewing. In October 1808, the Revenant (renamed Iena), was captured by a British warship. Using a proper filter is very important as some improvised filters reduce visible light while passing either infrared or ultraviolet rays that can still damage the eye. In the meantime, Decaen had confiscated all Surcouf's possessions in the Indian Ocean. Suitable filters are available at welding supply shops and camera stores. After a heated argument with Decaen, Surcouf acquired the frigate La Sémillante, renamed it Le Charles, and sailed it back to France.

Viewing the Sun through light-concentrating optics such as binoculars is hazardous without an attenuating (ND) filter to dim the sunlight. The governor of Isle de France, General Charles Decaen, seized the Revenant for the defense of the island. Brief viewing of the full direct Sun with the naked eye is unpleasant but generally safe.^[18]. In two campaigns, the latter captured about 20 ships, including the large 34-gun Portuguese Conceçao. Direct viewing of the Sun with the naked eye delivers about 4 milliwatts of sunlight to the retina that is in the solar image, heating it up and potentially (though not normally) damaging it. He then decided to stay on the island, leaving the campaign to his second-in-command (and cousin) Joseph Potier. Looking directly at the Sun when it is high in the sky causes temporary bleaching of the photosensitive pigments in the retina, which makes phosphene visual artifacts and may cause temporary partial blindness. He returned to Isle de France on the 31st of February 1808.

Sunlight is very bright, and looking directly at the Sun is painful to the eyes. During the subsequent campaign, which was to be his last, Surcouf captured 16 British ships, partly because British ships tended to lower their flag as soon as they identified their opponent. The energy stored in petroleum is thought to have been converted from sunlight by photosynthesis in the distant past. Surcouf arrived at Isle de France in June, defeating the British blockade and capturing several ships on the journey. Photosynthesis by plants captures the energy of sunlight and converts it to chemical form (oxygen and reduced carbon compounds), while direct heating or electrical conversion by solar cells are used by solar power equipment to generate electricity or do other useful work. Le Revenant was constructed under special directives by Surcouf himself, with a completely coppered hull, and a remarkable (for the time) top speed of 12 knots. This energy can be harnessed through several natural and synthetic processes. On the 2nd of March, Surcouf returned to sea on a specially-built three-mast, the 20-gun Revenant.

Sunlight on the surface of Earth is attenuated by the Earth's atmosphere, so that less power arrives at the surface — closer to 1000 watts per directly exposed square meter in clear conditions when the Sun is near the zenith. In 1807, a British vessel captured Nicolas Surcouf. near Earth. Their achievements, however, were somewhat less impressive than Surcouf's own: four of the corsairs were captured by British warships, and 5 campaigns turned a deficit. from the Sun, i.e. In 1804, Surcouf went into business as ship-owner, and equipped 14 privateers in the Indian Ocean (among them his brother Nicolas Surcouf and his cousin Joseph Potier). It is about 1370 watts per square meter of area, one A.U. Surcouf left in good terms, and was made officer of the Légion d'Honneur on the 18th of July 1804.

The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. His arguments did not fall on deaf ears; in 1805, Napoleon chose a blockade against England rather than direct confrontation, and allowed privateers to operate with relative impunity. Sunlight — that is, light radiated from the surface of the Sun — is thought to be the main source of energy near the surface of Earth. by attacking its merchant navy) rather than direct naval assault. Thus, the Sun was considered by Greek astronomers to be one of the seven planets (Greek planetes "wanderer"), after which the seven days of the week are named in some languages. Surcouf, however, refused, for two reasons: first, he would not have been allowed to operate as independently as he desired; and second, he believed that the war against England should be waged with economic means (i.e. With respect to the fixed stars, the Sun appears from Earth to revolve once a year along the ecliptic through the zodiac. In 1803, at the breaking of the Treaty of Amiens, First Consul Napoleon Bonaparte personally offered him the title of captain and command of a frigate squadron in the Indian Ocean.

It was only after Einstein's theory of mass-energy convertibility in the early 20th century that it was finally understood that the sun runs on nuclear fusion and is billions of years old, with several other billion to go. He settled in Saint-Malo, married, and spent six years in retirement, as a businessman. In the early years of the modern scientific era, it was proposed that the Sun extracted its energy from friction of its gas masses, which would yield a Sun no older than a few million years, with a few more million years to go. On the 13th of April 1801, though chased by British warships, he arrived in La Rochelle. For teaching this heresy he was imprisoned by the authorities and sentenced to death (though later released through the intervention of Pericles). He became a living legend in France and, in England, a public enemy whose capture was valued at 5 millions francs, although he was noted for the discipline of his crew and his humane treatment of prisoners. One of the first people in the Western world to offer a scientific explanation for the sun was the Greek philosopher Anaxagoras, who reasoned that it was a giant flaming ball of metal even larger than the Peleponessus, and not the chariot of Helios. Despite being outnumbered three to one, the French managed to seize control of the Kent.

In many prehistoric and ancient cultures, the Sun was thought to be a deity or other supernatural phenomenon. On the October 7th, 1800, in the Bay of Bengal, La Confiance met the 38-gun Kent, a 1200-ton East Indiaman with 400 men and a company of naval riflemen. Mankind's most fundamental understanding of the Sun is as the luminous disk in the heavens whose presence above the horizon creates day, and whose absence causes night. Beginning in March, he led a brilliant campaign which resulted in the capture of nine British ships. This stellar evolution scenario is typical of low to medium mass stars. In May, 1800, Surcouf took command of La Confiance, a fine and fast 18-gun frigate from Bordeaux undergoing repairs in Isle de France. The Sun will then evolve into a white dwarf, slowly cooling over eons. He captured a British brig and an American merchantman before returning to Isle de France.

Following the red giant phase, giant thermal pulsations will cause the Sun to throw off its outer layers forming a planetary nebula. Surcouf later had to flee before the 56-gun frigate Sybille, throwing eight guns overboard to out-sail the British warship. While it is likely that the expansion of the outer layers of the Sun will reach the current position of Earth's orbit, recent research suggests that mass lost from the Sun earlier in its red giant phase will cause the Earth's orbit to move further out, preventing it from being engulfed. On the 11th of November, the 20-gun Auspicious was captured, with a cargo worth in excess of one million francs. Helium fusion will begin when the core temperature reaches about 3×10⁸ K. He captured four ships in the South Atlantic, and two others near Sumatra in February 1799. Instead, in 4-5 billion years it will enter its red giant phase, its outer layers expanding as the hydrogen fuel in the core is consumed and the core contracts and heats up. He returned to sea in Nantes in August 1798, as captain of the 18-gun Clarisse, with 105 men.

Our Sun does not have enough mass to explode as a supernova, and its mass is below the Chandrasekhar limit. Following a dispute with the governor of Isle de France, Surcouf sailed to France to receive his letter of marque. This is suggested by a high abundance of heavy elements such as iron, gold and uranium in the solar system: the most plausible ways that these elements could be produced are by endothermic nuclear reactions during a supernova or by transmutation via neutron absorption inside a massive first generation star. The capture was declared legal, but in the absence of a letter of marque, the authorities retained the entire cargo (a portion of which normally goes to the corsair). The Sun is thought to be a second-generation star, whose formation may have been triggered by shockwaves from a nearby supernova. Surcouf was welcomed as a saviour in the famished Port Louis. It returned to Earth in 2004 and is undergoing analysis, but it was damaged by crash-landing when its parachute failed to deploy on reentry to Earth's atmosphere. After a brief gunnery exchange, the British ships lowered their flag and were brought back to Mauritius, with their cargo of rice and mais.

A solar wind sample return mission, Genesis, was designed to allow astronomers to directly measure the composition of solar material. On the 3rd of June 1794, Surcouf sailed with the 4-gun ship La Créole, with a complement of 30 men, with orders to bring rice to Mauritius, and encountered three English ships escorted by the 26-gun Triton; he used a technicality to engage combat in self-defence, by not flying his colours until the English ships requested them by firing a warning shot (a naval convention of the time), which Surcouf later reported to consider an aggression. Elemental abundances in the photosphere are well known from spectroscopic studies, but the composition of the interior of the Sun is much less well known. However, the Convention frowned at privateers, and it was difficult to obtain a letter of marque. It has proved so useful that a follow-on mission, the Solar Dynamics Observatory, is planned for launch in 2008. He was made a captain in Isle de France, and expressed his ambition to wage corsair warfare against England. Originally a two-year mission, SOHO is now over ten years old (as of late 2005). Surcouf was one of the heroes of the day.

To obtain an uninterrupted view of the Sun, the European Space Agency and NASA cooperatively launched the Solar and Heliospheric Observatory (SOHO) on December 2, 1995. Surcouf was made a second officer of the frigate Cybèle, which, with another frigate and a brig, and with less than half their firepower, engaged and repelled the attackers. The North/South swing in apparent angle is the main source of seasons on Earth. Isle de France was threatened by two vessels (54-gun and 60-gun) commanded by Commodore Osborn. The most obvious variation in the Sun's apparent position through the year is a North/South swing over 47 degrees of angle, due to the 23.5 degree tilt of the Earth, but there is an East/West component as well. He sailed to Isle de France (present-day Mauritius) in August on a commercial brig, and was informed on his arrival of the outbreak of war against Britain. The shape described by the Sun's position, considered at the same time each day for a complete year, is called the analemma, and resembles a figure 8, aligned along the North/South direction. In 1792 he came back to Saint-Malo and discovered the political changes France had undergone in the wake of the French Revolution.

Observed from Earth, the path of the Sun across the sky varies throughout the year. Between 1789 and 1791, he participated in slave trade between Mozambique and Madagascar. the interplanetary medium) in a magnetic field, induces electric currents which in turn generates magnetic fields, and in this respect it behaves like an MHD dynamo. At age 15, he enlisted on a merchantman to India. Magnetohydrodynamic (MHD) theory predicts that the motion of a conducting fluid (e.g. At 13, he escaped his professors and stole a small craft to prove his ability to sail; he was subsequently caught in a tempest and had to be rescued. But satellite observations show that it is about 100 times greater at around 10^-9 tesla. He attended a religious school and was educated by the Jesuits.

If space were a vacuum, then the Sun's 10^-4 tesla magnetic dipole field would reduce with the cube of the distance to about 10^-11 tesla. Surcouf was born in December 1773 in Saint-Malo, a fortified town in Brittany, traditionally a corsair stronghold. The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated. During his lengendary career, he captured 47 ships and was renowned for his gallantry and chivalry, earning the nickname of Roi des Corsaires ("King of Privateers"). The influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium creates the largest structure in the Solar System, the Heliospheric current sheet. Robert Surcouf (1773–1827) was a famous French privateer. The magnetic field of the sun reverses once for each 11-year sunspot cycle. See French ship Surcouf for ships name in the honour of Surcouf.

The solar activity cycle includes old magnetic fields being stripped off the Sun's surface starting from one pole and ending at the other. Surcouf happened to be a descendant of Duguay-Trouin on the side of his mother. (See magnetic reconnection). In Master and Commander: The Far Side of the World, a British ship (ironically enough) escapes a French privateer using this same trick. The differential rotation of the Sun's latitudes causes its magnetic field lines to become twisted together over time, causing magnetic field loops to erupt from the Sun's surface and trigger the formation of the Sun's dramatic sunspots and solar prominences. The manoeuver consisting in setting up a decoy a night by planting a lantern on a small boat was executed by Surcouf to successfully escape the British frigate HMS Sybille. This makes it possible for the Sun to rotate faster at its equator (about 25 days) than it does at higher latitudes (28 days near its poles). The phrase "A man fights for what he lacks the most!" is said by "cap'tain Red" in Polansky's Pirates!.

All matter in the Sun is in the form of gas and plasma due to its high temperatures. On spotting the much more powerful Kent:. Others suggest that cosmic rays might strongly influence the Earth's climate, and that their flux was much higher in the early history of the solar system ^[17]. Discussing with a British officer:. Some scientists have suggested that the young Earth's atmosphere contained much larger quantities of greenhouse gases such as carbon dioxide and/or ammonia than are present today ^[16]. In fact, the young Earth was actually warmer than it is today.

However, the geologic record shows that the Earth has remained at a fairly constant temperature throughout its history. Such a weak star would not have been able to sustain liquid water on the Earth's surface, and thus life should not have been able to develop. Theoretical models of the sun's development suggest that 3.8 to 2.5 billion years ago, during the Archean period, the Sun was only about 75 percent as bright as it is today. One possible candidate to explain coronal heating is continuous flaring at small scales ^[15], but this is still an open topic of investigation.

Current research focus has therefore shifted towards flare heating mechanisms. In addition, Alfven waves do not easily dissipate in the corona ^[14]. All waves except Alfven waves have been found to dissipate or refract before reaching the corona (^[12], ^[13]). Currently, it is unclear whether waves are an efficient heating mechanism.

^[8], ^[9], ^[10], ^[11]. The other proposed mechanism is flare heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in the form of solar flares and waves. These waves travel upward and dissipate in the corona, depositing their energy in the ambient gas in the form of heat. Two main mechanisms have been proposed to explain coronal heating: Wave heating, in which sound, gravitational and magnetohydrodynamic waves are produced by turbulence in the convection zone.

It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere. The high temperature of the corona shows that it is heated by something other than the photosphere. Above it lies the solar corona with a temperature of one million kelvins. The optical surface of the Sun (the photosphere) is known to have a temperature of about 6,000 K.

Thus, measurement and theory have been reconciled. It has recently been found that neutrinos have rest mass, and can therefore transform into harder-to-detect varieties of neutrinos while en route from the Sun to Earth in a process known as neutrino oscillation ^[7]. Several neutrino observatories were constructed, including the Sudbury Neutrino Observatory and Kamiokande to try to measure the solar neutrino flux. For some time it was thought that the number of neutrinos produced by the nuclear reactions in the Sun was only a third of the number predicted by theory, a result that was termed the solar neutrino problem.

The temperature of the corona is several megakelvins. The low corona, which is very near the surface of the Sun, has a particle density of 10¹¹/m³ (Earth's atmosphere near sea level has a particle density of about 2x10²⁵/m³). The corona merges smoothly with the solar wind that fills the solar system and heliosphere. The corona is the extended outer atmosphere of the Sun, which is much larger in volume than the Sun itself.

It is called the chromosphere from the Greek root chroma, meaning color, because the chromosphere is visible as a colored flash at the beginning and end of total eclipses of the Sun. Above the visible surface of the Sun is a thin layer, about 2,000km thick, that is dominated by a spectrum of emission and absorption lines. This part of the Sun is cool enough to support simple molecules such as carbon monoxide and water which can be detected by their absorption spectra. It is about 4,000 K.

The coolest layer of the Sun is the temperature minimum region about 500km above the photosphere. They can be viewed with telescopes operating across the electromagnetic spectrum, from radio through visible light to gamma rays. The parts of the Sun above the photosphere are referred to collectively as the solar atmosphere. The photosphere has a particle density of about 10²³/m³ (this is about 1% of the particle density of Earth's atmosphere at sea level).

Sunlight has approximately a black-body spectrum that indicates its temperature is about 6,000 K, interspersed with atomic absorption lines from the tenuous layers above the photosphere. Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H^- ions. The change in opacity has to do with the decreasing amount of H^- ions, which absorb visible light easily. Above the photosphere, sunlight is free to propagate into space and its energy escapes the Sun entirely.

The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light. The turbulent convection of this outer part of the solar interior gives rise to a 'small-scale' dynamo that produces magnetic north and south poles all over the surface of the Sun. The thermal columns in the convection zone form an imprint on the surface of the Sun, in the form of the solar granulation and supergranulation. Convective overshoot is thought to occur at the base of the convection zone, carrying turbulent downflows into the outer layers of the radiative zone.

Once the material cools off at the surface, it plunges back downward to the base of the convection zone, to receive more heat from the top of the radiative zone. As a result, thermal convection occurs as thermal columns carry hot material to the surface (photosphere) of the Sun. From about 0.7 solar radii to 1.0 solar radii, the material in the Sun is not dense enough or hot enough to transfer the heat energy of the interior outward via radiation. Because of this, it can take a photon nearly 1,000,000 years to reach the photosphere.

Heat is transferred by ions of hydrogen and helium emitting photons, which travel a brief distance before being re-absorbed by other ions. In this zone, there is no thermal convection: while the material grows cooler with altitude, this temperature gradient is slower than the adiabatic lapse rate and hence cannot drive convection. From about 0.2 to about 0.7 solar radii, the material is hot and dense enough that thermal radiation is sufficient to transfer the intense heat of the core outward. Neutrinos are also released in the fusion reactions in the core, but unlike photons they very rarely interact with matter, and so almost all are able to escape the Sun immediately.

Upon reaching the surface after a final trip through the convective outer layer, the photons escape as visible light. 65) to as little as 17,000 years [6]. Lewis, The Illustrated Encyclopedia of the Universe, Harmony Books, New York, 1983, p. Estimates of the "photon travel time" range from as much as 50 million years (Richard S.

The high-energy photons (gamma and X rays) released in fusion reactions take a long time to reach the Sun's surface, slowed down by the indirect path taken, as well as constant absorption and re-emission at lower energies in the solar mantle (see below). All of the energy of the interior fusion must travel through the successive layers to the solar photosphere, before it escapes to space. The core extends from the center of the Sun to about 0.2 solar radii, and is the only part of the Sun where an appreciable amount of heat is produced by fusion: the rest of the star is heated by energy that is transferred outward. About 8.9×10³⁷ protons (hydrogen nuclei) are converted to helium nuclei every second, releasing energy at the matter-energy conversion rate of 4.26 million tonnes per second or 383 yottawatts (9.15×10¹⁶ tons of TNT per second).

At the center of the Sun, where its density reaches up to 150,000 kg/m³ (150 times the density of water on Earth), thermonuclear reactions (nuclear fusion) convert hydrogen into helium, producing the energy that keeps the Sun in a state of equilibrium. Computer modeling of the Sun is also used as a theoretical tool to investigate its deep layers. However, just as the study of the waves generated by earthquakes (seismology) can be used to study the interior structure of the Earth, helioseismology, the study of sound waves that travel through the Sun's interior, has also contributed greatly to our understanding of the Sun's structure. The solar interior is not directly observable and the Sun itself is opaque to electromagnetic radiation.

Most of the mass is within about 0.7 radii. This is simply the layer above which the gases are too cool or too thin to radiate a significant amount of light. The Sun's radius is measured from centre to the edges of the photosphere. Nevertheless, the Sun has a well-defined interior structure, described below.

The Sun does not have a definite boundary as rocky planets do, as the density of its gases drops off following an approximately exponential relationship with distance from the centre of the Sun. The mass of the Sun is so comparatively great that the center of mass of the solar system is generally within the bounds of the Sun itself. Tidal effects from the planets do not significantly affect the shape of the Sun, although the Sun itself orbits the center of mass of the solar system, which is offset from the Sun's center mostly because of the large mass of Jupiter. This is because the centrifugal effect of the Sun's slow rotation is 18 million times weaker than its surface gravity (at the equator).

The Sun is a near-perfect sphere, with an oblateness estimated at about 9 millionths, which means the polar diameter differs from the equatorial by about 10 km. The astronomical symbol for the Sun is a circle with a point at its centre: . Compared to the average movement of other stars in the area, the Sun is moving with a speed of 20 km/s toward the star Vega. The orbital speed is 217 km/s, equivalent to one light year every 1400 years, and one AU every 8 days.

The Sun orbits the center of the Milky Way galaxy at a distance of about 25,000 to 28,000 light-years from the galactic centre, completing one revolution in about 226 million years. Its current age is thought to be about 4.5 billion years, a figure which is determined using computer models of stellar evolution, and nucleocosmochronology ^[5]. The Sun has a predicted main sequence lifetime of about 10 billion years. The Sun has a spectral class of G2V, with the G2 meaning that its color is yellow and its spectrum contains spectral lines of ionized and neutral metals as well as very weak hydrogen lines [3], and the V signifying that it, like most stars, is a "main sequence" star [4].

The Sun is classified as a main sequence star, which means it is in a state of "hydrostatic balance", neither contracting nor expanding, and is generating its energy through nuclear fusion of hydrogen nuclei into helium. . See below for details. Looking directly at the Sun can damage the retina and one's eyesight.