DragonA dragon is a mythological creature, typically depicted as a large and powerful serpent or other reptile, with magical or spiritual qualities. OverviewThe various figures now called dragons most likely have no single origin, but spontaneously came to be in several different cultures around the world, based loosely on the appearance of a snake and possibly fossilized dinosaur and Tertiary mammal megafauna remains. Chinese dragons (among others) or Long are generally seen as benevolent, whereas European dragons are usually malevolent. However, malevolent dragons are not restricted to Europe and also occur in Persian mythology (see Azi Dahaka) and other cultures. Malevolent dragons are prominent figures in Christian belief. In Revelation 12:3, an enormous red dragon with seven heads is described, whose tail sweeps one third of the stars from heaven down to earth (held to be symbolic of the fall of the angels). The Latin word for a dragon, draco, actually means snake or serpent and is so connected to the Christian association of snakes and the Devil. The biblical dragon carries over thirty possible references, with the fire-breathing Leviathan described in Job 41. Strong's Hebrew 03882: [1], 08568, 08577, and Greek 1404. In iconography, some Christian Saints are depicted in the act of killing a dragon: for instance, Saint George in Egyptian Coptic iconography [2], at the coat of arms of Moscow, or, in Italy, Saint Mercurialis, who was the first bishop of the city of Forlì. In the Book of Job Chapter 41, the sea monster Leviathan, which has some dragonlike characteristics, is described as God talks about the "king of beasts" that lived upon the Earth at a former time. Leviathan was birthed from an enzyme from the garden of Eden. God fed Leviathan to Israel while they wandered in the wilderness for forty years (Psalm 74:14). Dobrynya Nikitich slaying Zmey Gorynych, by Ivan Bilibin.In medieval symbolism, dragons were often symbolic of apostasy and treachery, but also of anger and envy, and eventfully symbolised great calamity. Several heads were symbolic of decadence and oppression, and also of heresy. They also served as symbols for independence, leadership and strength. Colors often determined the symbolism a dragon carried. In the hero's journey pattern, dragons represented fear. Dragons are often held to have major spiritual significance in various religions and cultures around the world. In many oriental cultures dragons were, and in some cultures still are, revered as representative of the primal forces of nature and the universe. Some believe that the dragon may have had a real-life counterpart from which the legends around the world arose — typically dinosaurs are mentioned as a possibility — but there is no evidence to support this claim. Another less common claim is that they are based upon some sort of flying machines possessed by some ancient, unknown culture. Both of these hypotheses are pseudoscience. Dragons are very popular in video games today, especially role-playing games. They are typically used as very powerful bosses and villains. In many games, a powerful character must overcome a dragon as a final challenge. The word "dragon" should not be confused with dragoon (infantry that moves around by horse, yet still fight as foot soldiers). However, numerous fantasy settings (such as the Final Fantasy games) make varying degrees of association between dragons and the dragoon character class (such as in the helmet of a dragoon-class character), and in the game Panzer Dragoon in which the player flies about on a dragon. Dragons of myth and folkoreDragon carving on Hopperstad stave church, Norway
Notable dragons in modern literature and culture
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However, numerous fantasy settings (such as the Final Fantasy games) make varying degrees of association between dragons and the dragoon character class (such as in the helmet of a dragoon-class character), and in the game Panzer Dragoon in which the player flies about on a dragon. Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation. The word "dragon" should not be confused with dragoon (infantry that moves around by horse, yet still fight as foot soldiers). 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. In many games, a powerful character must overcome a dragon as a final challenge. 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. They are typically used as very powerful bosses and villains. 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. Dragons are very popular in video games today, especially role-playing games. 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. Both of these hypotheses are pseudoscience. 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. Another less common claim is that they are based upon some sort of flying machines possessed by some ancient, unknown culture. The pupil is controlled by the total amount of light in the visual field, not by the brightest object in the field. Some believe that the dragon may have had a real-life counterpart from which the legends around the world arose — typically dinosaurs are mentioned as a possibility — but there is no evidence to support this claim. During partial eclipses of the Sun, another hazardous condition exists because of the way the eye responds to bright light. In many oriental cultures dragons were, and in some cultures still are, revered as representative of the primal forces of nature and the universe. Even brief glances at the midday Sun through unfiltered binoculars can cause permanent blindness.[19]. Dragons are often held to have major spiritual significance in various religions and cultures around the world. 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 the hero's journey pattern, dragons represented fear. 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. Colors often determined the symbolism a dragon carried. Suitable filters are available at welding supply shops and camera stores. They also served as symbols for independence, leadership and strength. Viewing the Sun through light-concentrating optics such as binoculars is hazardous without an attenuating (ND) filter to dim the sunlight. Several heads were symbolic of decadence and oppression, and also of heresy. Brief viewing of the full direct Sun with the naked eye is unpleasant but generally safe.[18]. In medieval symbolism, dragons were often symbolic of apostasy and treachery, but also of anger and envy, and eventfully symbolised great calamity. 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. God fed Leviathan to Israel while they wandered in the wilderness for forty years (Psalm 74:14). 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. Leviathan was birthed from an enzyme from the garden of Eden. Sunlight is very bright, and looking directly at the Sun is painful to the eyes. In the Book of Job Chapter 41, the sea monster Leviathan, which has some dragonlike characteristics, is described as God talks about the "king of beasts" that lived upon the Earth at a former time. The energy stored in petroleum is thought to have been converted from sunlight by photosynthesis in the distant past. In iconography, some Christian Saints are depicted in the act of killing a dragon: for instance, Saint George in Egyptian Coptic iconography [2], at the coat of arms of Moscow, or, in Italy, Saint Mercurialis, who was the first bishop of the city of Forlì. 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. Strong's Hebrew 03882: [1], 08568, 08577, and Greek 1404. This energy can be harnessed through several natural and synthetic processes. The biblical dragon carries over thirty possible references, with the fire-breathing Leviathan described in Job 41. 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. The Latin word for a dragon, draco, actually means snake or serpent and is so connected to the Christian association of snakes and the Devil. near Earth. In Revelation 12:3, an enormous red dragon with seven heads is described, whose tail sweeps one third of the stars from heaven down to earth (held to be symbolic of the fall of the angels). from the Sun, i.e. Malevolent dragons are prominent figures in Christian belief. It is about 1370 watts per square meter of area, one A.U. However, malevolent dragons are not restricted to Europe and also occur in Persian mythology (see Azi Dahaka) and other cultures. The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. Chinese dragons (among others) or Long are generally seen as benevolent, whereas European dragons are usually malevolent. 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. The various figures now called dragons most likely have no single origin, but spontaneously came to be in several different cultures around the world, based loosely on the appearance of a snake and possibly fossilized dinosaur and Tertiary mammal megafauna remains. 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. . With respect to the fixed stars, the Sun appears from Earth to revolve once a year along the ecliptic through the zodiac. A dragon is a mythological creature, typically depicted as a large and powerful serpent or other reptile, with magical or spiritual qualities. 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. Dragon Tales the animated children's series on PBS. 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. Rêve de Dragon). For teaching this heresy he was imprisoned by the authorities and sentenced to death (though later released through the intervention of Pericles). Dragons in Dungeons & Dragons and other fantasy role-playing games (e.g. 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. Pernese dragons, from the books by Anne McCaffrey. In many prehistoric and ancient cultures, the Sun was thought to be a deity or other supernatural phenomenon. Tolkien. 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. R. This stellar evolution scenario is typical of low to medium mass stars. R. The Sun will then evolve into a white dwarf, slowly cooling over eons. Smaug, from The Hobbit and Glaurung, from The Silmarillion by J. Following the red giant phase, giant thermal pulsations will cause the Sun to throw off its outer layers forming a planetary nebula. Puff the Magic Dragon, a poem, then song; dragons in children's culture. 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. Basilisk. Helium fusion will begin when the core temperature reaches about 3×108 K. Wyvern. 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. Griffin. Our Sun does not have enough mass to explode as a supernova, and its mass is below the Chandrasekhar limit. Dragon Relatives
Welsh dragon. A solar wind sample return mission, Genesis, was designed to allow astronomers to directly measure the composition of solar material. Tatar dragon. 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. Romanian dragons (Zmeu and Balaur). It has proved so useful that a follow-on mission, the Solar Dynamics Observatory, is planned for launch in 2008. Slavic dragon. Originally a two-year mission, SOHO is now over ten years old (as of late 2005). Serbian dragon. 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. Polish dragon. The North/South swing in apparent angle is the main source of seasons on Earth. Norse dragon. 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. Lindworm dragon. 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. Greek dragon. Observed from Earth, the path of the Sun across the sky varies throughout the year. French dragon. 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. Finnish dragon. Magnetohydrodynamic (MHD) theory predicts that the motion of a conducting fluid (e.g. Egyptian dragon. But satellite observations show that it is about 100 times greater at around 10-9 tesla. Celtic dragon. 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. European dragon
Korean dragon. The solar activity cycle includes old magnetic fields being stripped off the Sun's surface starting from one pole and ending at the other. Japanese dragon. (See magnetic reconnection). Indian dragon. 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. Chinese dragon. 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). Asian dragon
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. Although it is the nearest star to Earth and has been intensively studied by scientists, many questions about the Sun remain unanswered, such as why its outer atmosphere has a temperature of over 106 K when its visible surface (the photosphere) has a temperature of just 6,000 K. In about 5 billion years time the Sun will evolve into a red giant and then a white dwarf.[2]. It is thought that the Sun is about 5 billion years old, and is about halfway through its main sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. About 74% of its mass is hydrogen, with 25% helium and the rest made up of trace quantities of heavier elements. The Sun is a ball of plasma with a mass of about 2×1030 kg, which is somewhat higher than that of an average star. It is sometimes referred to by its Latin name, Sol. Its heat and light support almost all life on Earth. Earth orbits the Sun, as do many other bodies, including other planets, asteroids, meteoroids, comets and dust. The Sun is the star at the center of our Solar system. |