Geocentric model
In astronomy, the geocentric model is a superseded description of the Universe with Earth at the center. Under the geocentric model, the Sun, Moon and planets all orbited Earth; the geocentric model served as the predominant description of the cosmos in many ancient civilizations, such as those of Aristotle and Ptolemy. Two observations supported the idea. First, from anywhere on Earth, the Sun appears to revolve around Earth once per day. While the Moon and the planets have their own motions, they appear to revolve around Earth about once per day; the stars appeared to be fixed on a celestial sphere rotating once each day about an axis through the geographic poles of Earth. Second, Earth seems to be unmoving from the perspective of an earthbound observer. Ancient Greek, ancient Roman, medieval philosophers combined the geocentric model with a spherical Earth, in contrast to the older flat Earth model implied in some mythology; the ancient Jewish Babylonian uranography pictured a flat Earth with a dome-shaped, rigid canopy called the firmament placed over it.
However, the ancient Greeks believed that the motions of the planets were circular and not elliptical, a view, not challenged in Western culture until the 17th century, when Johannes Kepler postulated that orbits were heliocentric and elliptical. In 1687, Newton showed; the astronomical predictions of Ptolemy's geocentric model were used to prepare astrological and astronomical charts for over 1500 years. The geocentric model held sway into the early modern age, but from the late 16th century onward, it was superseded by the heliocentric model of Copernicus and Kepler. There was much resistance to the transition between these two theories; some Christian theologians were reluctant to reject a theory. Others felt a unknown theory could not subvert an accepted consensus for geocentrism; the geocentric model entered Greek philosophy at an early point. In the 6th century BC, Anaximander proposed a cosmology with Earth shaped like a section of a pillar, held aloft at the center of everything; the Sun and planets were holes in invisible wheels surrounding Earth.
About the same time, Pythagoras thought that the Earth was a sphere, but not at the center. These views were combined, so most educated Greeks from the 4th century BC on thought that the Earth was a sphere at the center of the universe. In the 4th century BC, two influential Greek philosophers and his student Aristotle, wrote works based on the geocentric model. According to Plato, the Earth was a sphere; the stars and planets were carried around the Earth on spheres or circles, arranged in the order: Moon, Venus, Mars, Saturn, fixed stars, with the fixed stars located on the celestial sphere. In his "Myth of Er", a section of the Republic, Plato describes the cosmos as the Spindle of Necessity, attended by the Sirens and turned by the three Fates. Eudoxus of Cnidus, who worked with Plato, developed a less mythical, more mathematical explanation of the planets' motion based on Plato's dictum stating that all phenomena in the heavens can be explained with uniform circular motion. Aristotle elaborated on Eudoxus' system.
In the developed Aristotelian system, the spherical Earth is at the center of the universe, all other heavenly bodies are attached to 47–55 transparent, rotating spheres surrounding the Earth, all concentric with it. These spheres, known as crystalline spheres, all moved at different uniform speeds to create the revolution of bodies around the Earth, they were composed of an incorruptible substance called aether. Aristotle believed that the Moon was in the innermost sphere and therefore touches the realm of Earth, causing the dark spots and the ability to go through lunar phases, he further described his system by explaining the natural tendencies of the terrestrial elements: Earth, fire, air, as well as celestial aether. His system held that Earth was the heaviest element, with the strongest movement towards the center, thus water formed a layer surrounding the sphere of Earth; the tendency of air and fire, on the other hand, was to move upwards, away from the center, with fire being lighter than air.
Beyond the layer of fire, were the solid spheres of aether in which the celestial bodies were embedded. They, were entirely composed of aether. Adherence to the geocentric model stemmed from several important observations. First of all, if the Earth did move one ought to be able to observe the shifting of the fixed stars due to stellar parallax. In short, if the Earth was moving, the shapes of the constellations should change over the course of a year. If they did not appear to move, the stars are either much farther away than the Sun and the planets than conceived, making their motion undetectable, or in reality they are not moving at all; because the stars were much further away than Greek astronomers postulated, stellar parallax was not detected until the 19th century. Therefore, the Greeks chose the simpler of the two explanations. Another observ
Hermann Bondi
Sir Hermann Bondi was an Anglo-Austrian mathematician and cosmologist. He is best known for developing the Steady State theory of the universe with Fred Hoyle and Thomas Gold as an alternative to the Big Bang theory, he contributed to the theory of general relativity, was the first to analyze the inertial and gravitational interaction of negative mass. Bondi was born in the son of a medical doctor, he was brought up in Vienna. He showed early prodigious ability at mathematics, was recommended to Arthur Eddington by Abraham Fraenkel. Fraenkel was a distant relation, the only mathematician in the extended family, Hermann's mother had the foresight to engineer a meeting between her young son and the famous man, knowing that this might be the key to enabling him to follow his wishes and become a mathematician himself. Eddington encouraged him to travel to England to read the mathematical tripos at Trinity College, Cambridge, he arrived in Cambridge in 1937. Realizing the perilous position of his parents in 1938, shortly before the Anschluss, he sent them a telegram telling them to leave Austria at once.
They managed to reach Switzerland, settled in New York. In the early years of World War II, he was interned on the Isle of Man and in Canada as a friendly enemy alien. Other internees included Max Perutz. Bondi and Gold had been released by the end of 1941, worked with Fred Hoyle on radar at the Admiralty Signals Establishment, he became a British subject in 1946. Bondi lectured in mathematics at the University of Cambridge from 1945 to 1954, he was a fellow of Trinity 1943-9 and 1952-4 In 1948, Bondi and Gold formulated the Steady State theory, which holds that the universe is expanding but matter is created to form new stars and galaxies to maintain a constant average density. Steady State theory was eclipsed by the rival Big Bang theory with the discovery of the cosmic microwave background. Bondi was one of the first to appreciate the nature of gravitational radiation, introducing Bondi radiation coordinates, the Bondi k-calculus, the notions of Bondi mass and Bondi news, writing review articles.
He popularized the sticky bead argument, said to be due, anonymously, to Richard Feynman, for the claim that physically meaningful gravitational radiation is indeed predicted by general relativity, an assertion, controversial up until about 1955. A 1947 paper revived interest in the Lemaître–Tolman metric, an inhomogeneous, spherically symmetric dust solution. Bondi contributed to the theory of accretion of matter from a cloud of gas onto a star or a black hole, working with Raymond Lyttleton and giving his name to "Bondi accretion" and the "Bondi radius", he became a professor at King's College London in 1954, was given the title of Emeritus Professor there in 1985. He was secretary of the Royal Astronomical Society from 1956 to 1964. Bondi was active outside the confines of academic lecturing and research, he held many positions: Director-General of the European Space Research Organisation Chief Scientific Adviser to the Ministry of Defence Chief Scientific Adviser to the Department of Energy Chairman of the Natural Environment Research Council President of the Society for Research into Higher Education President of the Hydrographic Society Master of Churchill College, Cambridge.
He became a fellow of the Royal Society in 1959. He made a series of television programs called E=mc2 for the BBC in 1963, he was appointed a Knight Commander of the Bath in 1973. He was awarded the Einstein Society Gold Medal in 1983, the Gold Medal of the Institute of Mathematics and its Applications in 1988, the G. D. Birla International Award for Humanism, the Gold Medal of the Royal Astronomical Society in 2001, he was awarded an Honorary Degree by the University of Bath in 1974. His report into the flooding of London in 1953 led to the building of the Thames Barrier, he supported the proposal for a Severn Barrage to generate electricity, but this project was not carried forward. His papers from 1940 to 2000 are archived in 109 archive boxes by the Janus Project, his parents were Jewish. He was president of the British Humanist Association from 1982 to 1999, president of the Rationalist Press Association from 1982, he was one of the signers of the Humanist Manifesto. He married Christine Stockman a mathematician and astronomer, in 1947.
Together, they had two sons and three daughters, one of whom is Professor Liz Bondi, feminist geographer at the University of Edinburgh. He died in Cambridge in 2005, aged 85. and his ashes were scattered at Anglesey Abbey near Cambridge. Christine died in 2015. Christina Sormani, C. Denson Hill, Paweł Nurowski, Lydia Bieri, David Garfinkle, Nicolás Yunes. "A two-part feature: The Mathematics of Gravitational waves". Notices of the American Mathematical Society. American Mathematical Society. 64: 684-707. ISSN 1088-9477. CS1 maint: Uses authors parameter
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance-era mathematician and astronomer who formulated a model of the universe that placed the Sun rather than the Earth at the center of the universe, in all likelihood independently of Aristarchus of Samos, who had formulated such a model some eighteen centuries earlier. The publication of Copernicus' model in his book De revolutionibus orbium coelestium, just before his death in 1543, was a major event in the history of science, triggering the Copernican Revolution and making a pioneering contribution to the Scientific Revolution. Copernicus was born and died in Royal Prussia, a region, part of the Kingdom of Poland since 1466. A polyglot and polymath, he obtained a doctorate in canon law and was a mathematician, physician, classics scholar, governor and economist. In 1517 he derived a quantity theory of money—a key concept in economics—and in 1519 he formulated an economic principle that came to be called Gresham's law. Nicolaus Copernicus was born on 19 February 1473 in the city of Thorn, in the province of Royal Prussia, in the Crown of the Kingdom of Poland.
His father was a merchant from Kraków and his mother was the daughter of a wealthy Toruń merchant. Nicolaus was the youngest of four children, his brother Andreas became an Augustinian canon at Frombork. His sister Barbara, named after her mother, became a Benedictine nun and, in her final years, prioress of a convent in Chełmno, his sister Katharina married the businessman and Toruń city councilor Barthel Gertner and left five children, whom Copernicus looked after to the end of his life. Copernicus never married and is not known to have had children, but from at least 1531 until 1539 his relations with Anna Schilling, a live-in housekeeper, were seen as scandalous by two bishops of Warmia who urged him over the years to break off relations with his "mistress". Copernicus' father's family can be traced to a village in Silesia near Nysa; the village's name has been variously spelled Kopernik, Copernic, Kopernic and today Koperniki. In the 14th century, members of the family began moving to various other Silesian cities, to the Polish capital, Kraków, to Toruń.
The father, Mikołaj the Elder the son of Jan, came from the Kraków line. Nicolaus was named after his father, who appears in records for the first time as a well-to-do merchant who dealt in copper, selling it in Danzig, he moved from Kraków to Toruń around 1458. Toruń, situated on the Vistula River, was at that time embroiled in the Thirteen Years' War, in which the Kingdom of Poland and the Prussian Confederation, an alliance of Prussian cities and clergy, fought the Teutonic Order over control of the region. In this war, Hanseatic cities like Danzig and Toruń, Nicolaus Copernicus's hometown, chose to support the Polish King, Casimir IV Jagiellon, who promised to respect the cities' traditional vast independence, which the Teutonic Order had challenged. Nicolaus' father was engaged in the politics of the day and supported Poland and the cities against the Teutonic Order. In 1454 he mediated negotiations between Poland's Cardinal Zbigniew Oleśnicki and the Prussian cities for repayment of war loans.
In the Second Peace of Thorn, the Teutonic Order formally relinquished all claims to its western province, which as Royal Prussia remained a region of the Crown of the Kingdom of Poland until the First and Second Partitions of Poland. Copernicus's father married Barbara Watzenrode, the astronomer's mother, between 1461 and 1464, he died about 1483. Nicolaus' mother, Barbara Watzenrode, was the daughter of a wealthy Toruń patrician and city councillor, Lucas Watzenrode the Elder, Katarzyna, mentioned in other sources as Katarzyna Rüdiger gente Modlibóg; the Modlibógs were a prominent Polish family, well known in Poland's history since 1271. The Watzenrode family, like the Kopernik family, had come from Silesia from near Świdnica, after 1360 had settled in Toruń, they soon became one of most influential patrician families. Through the Watzenrodes' extensive family relationships by marriage, Copernicus was related to wealthy families of Toruń, Gdańsk and Elbląg, to prominent Polish noble families of Prussia: the Czapskis, Działyńskis, Konopackis and Kościeleckis.
Lucas and Katherine had three children: Lucas Watzenrode the Younger, who would become Bishop of Warmia and Copernicus's patron. Lucas Watzenrode the Elder, a wealthy merchant and in 1439–62 president of the judicial bench, was a decided opponent of the Teutonic Knights. In 1453 he was the delegate from Toruń at the Grudziądz conference that planned the uprising against them. During the ensuing Thirteen Years' War, he supported the Prussian cities' war effort with substantial monetary subsidies, with political activity in Toruń and Danzig, by fighting in battles at Łasin and Malbork, he died in 1462. Lucas Watzenrode the Younger, the astronomer's maternal uncle and patron, was educated at the University of Kraków and at the universities of Cologne and Bologna, he was a bitter opponent of the Teutonic Order, its Grand Master once referred to him as "the devil incarn
Thomas Gold
Thomas Gold was an Austrian-born astrophysicist, a professor of astronomy at Cornell University, a member of the U. S. National Academy of Sciences, a Fellow of the Royal Society. Gold was one of three young Cambridge scientists who in 1948 proposed the now abandoned "steady state" hypothesis of the universe. Gold's work crossed academic and scientific boundaries, into biophysics, aerospace engineering, geophysics. Gold was born on May 22, 1920 in Vienna, Austria to Max Gold, a wealthy Jewish industrialist who ran one of Austria's largest mining and metal fabrication companies, German former actress Josefine Martin. Following the economic downfall of the European mining industry in the late 1920s, Max Gold moved his family to Berlin, where he had taken a job as director of a metal trading company. Following the start of Nazi leader Adolf Hitler's anti-Jewish campaigns in 1933, Gold and his family left Germany because of his father's heritage; the family travelled through Europe for the next few years.
Gold attended boarding school at the Lyceum Alpinum Zuoz in Zuoz, where he proved to be a clever and physically and mentally aggressive individual. Gold finished his schooling at Zuoz in 1938, fled with his family to England after the German invasion of Austria in early 1938. Gold began studying mechanical sciences. In May 1940, just as Hitler was commencing his advance in Belgium and France, Gold was sent into internment as an enemy alien by the British government, it was on the first night of internment, at an army barracks in Bury St Edmunds, that he met his future collaborator and close friend, Hermann Bondi. Gold spent most of his nearly 15 months of internment in a camp in Canada, after which he returned to England and reentered Cambridge University, where he abandoned his study of mechanical sciences for physics. After graduating with a pass degree in June 1942, Gold worked as an agricultural labourer and lumberjack in northern England before joining Bondi and Fred Hoyle on naval research into radar ground clutter near Dunsfold, Surrey.
The three men would spend their off-duty hours in "intense and wide-ranging scientific discussion" on topics such as cosmology and astrophysics. Within months, Gold was placed in charge of constructing new radar systems. Gold determined how landing craft could use radar to navigate to the appropriate landing spot on D-Day and discovered that the German navy had fitted snorkels to its U-boats, making them operable underwater while still taking in air from above the surface. After the war and Bondi returned to Cambridge, while Gold stayed with naval research until 1947, he began working at Cambridge's Cavendish Laboratory to help construct the world's largest magnetron, a device invented by two British scientists in 1940 that generated intense microwaves for radar. Soon after, Gold joined R. J. Pumphrey, a zoologist at the Cambridge Zoology Laboratory who had served as the deputy head of radar naval research during the war, to study the effect of resonance on the human ear, he found that the degree of resonance observed in the cochlea was not in accordance with the level of damping that would be expected from the viscosity of the watery liquid that fills the inner ear.
In 1948, Gold hypothesized that the ear operates by "regeneration", in that electromechanical action occurs when electrical energy is used to counteract the effects of damping. Although Gold won a prize fellowship from Trinity College for his thesis on the regeneration and obtained a junior lectureship at the Cavendish Laboratory, his theory was ignored by ear specialists and physiologists, such as future Nobel Prize winner Georg von Békésy, who did not believe the cochlea operated under a feedback system. In the 1970s, researchers discovered that Gold's hypothesis had been correct – the ear contained microscopic hair cells that operated on a feedback mechanism to generate resonance. Gold began discussing problems in physics with Hoyle and Bondi again, centering on the issues over redshift and Hubble's law; this led the three to all start questioning the Big Bang theory proposed by Georges Lemaître in 1931 and advanced by George Gamow, which suggested that the universe expanded from an dense and hot state and continues to expand today.
As recounted in a 1978 interview with physicist and historian Spencer R. Weart, Gold believed that there was reason to think that the creation of matter was "done all the time and none of the problems about fleeting moments arise, it can be just in a steady state with the expansion taking things apart as fast as new matter comes into being and condenses into new galaxies". Two papers were published in 1948 discussing the "steady-state theory" as an alternative to the Big Bang: one by Gold and Bondi, the other by Hoyle. In their seminal paper and Bondi asserted that although the universe is expanding, it does not change its look over time, they proposed the perfect cosmological principle as the underpinning of their theory, which held that the universe is homogeneous and isotropic in space and time. On the large scale, they argued that there "is nothing outstanding about any place in the universe, that those differences which do exist are only of local significance. However, since the universe was not characterized by a lack of evolution, distinguishing features or recognizable direction of time, they postulated that there had to be large-scale motions in the universe.
They highlighted two possible types of motion: large-scale expansion and its reverse, large-scale contraction. They estim
Proper motion
Proper motion is the astronomical measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distant stars. The components for proper motion in the equatorial coordinate system are given in the direction of right ascension and of declination, their combined value is computed as the total proper motion. It has dimensions of angle per time arcseconds per year or milliarcseconds per year. Knowledge of the proper motion and radial velocity allows calculations of true stellar motion or velocity in space in respect to the Sun, by coordinate transformation, the motion in respect to the Milky Way. Proper motion is not "proper", because it includes a component due to the motion of the Solar System itself. Over the course of centuries, stars appear to maintain nearly fixed positions with respect to each other, so that they form the same constellations over historical time.
Ursa Major or Crux, for example, looks nearly the same now. However, precise long-term observations show that the constellations change shape, albeit slowly, that each star has an independent motion; this motion is caused by the movement of the stars relative to the Solar System. The Sun travels in a nearly circular orbit about the center of the Milky Way at a speed of about 220 km/s at a radius of 8 kPc from the center, which can be taken as the rate of rotation of the Milky Way itself at this radius; the proper motion is a two-dimensional vector and is thus defined by two quantities: its position angle and its magnitude. The first quantity indicates the direction of the proper motion on the celestial sphere, the second quantity is the motion's magnitude expressed in arcseconds per year or milliarcsecond per year. Proper motion may alternatively be defined by the angular changes per year in the star's right ascension and declination, using a constant epoch in defining these; the components of proper motion by convention are arrived at.
Suppose an object moves from coordinates to coordinates in a time Δt. The proper motions are given by: μ α = α 2 − α 1 Δ t, μ δ = δ 2 − δ 1 Δ t; the magnitude of the proper motion μ is given by the Pythagorean theorem: μ 2 = μ δ 2 + μ α 2 ⋅ cos 2 δ, μ 2 = μ δ 2 + μ α ∗ 2, where δ is the declination. The factor in cos2δ accounts for the fact that the radius from the axis of the sphere to its surface varies as cosδ, for example, zero at the pole. Thus, the component of velocity parallel to the equator corresponding to a given angular change in α is smaller the further north the object's location; the change μα, which must be multiplied by cosδ to become a component of the proper motion, is sometimes called the "proper motion in right ascension", μδ the "proper motion in declination". If the proper motion in right ascension has been converted by cosδ, the result is designated μα*. For example, the proper motion results in right ascension in the Hipparcos Catalogue have been converted. Hence, the individual proper motions in right ascension and declination are made equivalent for straightforward calculations of various other stellar motions.
The position angle θ is related to these components by: μ sin θ = μ α cos δ = μ α ∗, μ cos θ = μ δ. Motions in equatorial coordinates can be converted to motions in galactic coordinates. For the majority of stars seen in the sky, the observed proper motions are small and unremarkable; such stars are either faint or are distant, have changes of below 10 milliarcseconds per year, do not appear to move appreciably over many millennia. A few do have significant motions, are called high-proper motion stars. Motions can be in seemingly random directions. Two or more stars, double stars or open star clusters, which are moving in similar directions, exhibit so-called shared or common proper motion, suggesting they may be gravitationally attached or share similar motion in space. Barnard's Star has the largest proper motion of all stars, moving at 10.3 seconds of arc per year. L
Bayesian inference
Bayesian inference is a method of statistical inference in which Bayes' theorem is used to update the probability for a hypothesis as more evidence or information becomes available. Bayesian inference is an important technique in statistics, in mathematical statistics. Bayesian updating is important in the dynamic analysis of a sequence of data. Bayesian inference has found application in a wide range of activities, including science, philosophy, medicine and law. In the philosophy of decision theory, Bayesian inference is related to subjective probability called "Bayesian probability". Bayesian inference derives the posterior probability as a consequence of two antecedents: a prior probability and a "likelihood function" derived from a statistical model for the observed data. Bayesian inference computes the posterior probability according to Bayes' theorem: P = P ⋅ P P where H stands for any hypothesis whose probability may be affected by data. There are competing hypotheses, the task is to determine, the most probable.
P, the prior probability, is the estimate of the probability of the hypothesis H before the data E, the current evidence, is observed. The evidence E corresponds to new data. P, the posterior probability, is the probability of H given E, i.e.. This is: the probability of a hypothesis given the observed evidence. P is the probability of observing E given H, is called the likelihood; as a function of E with H fixed, it indicates the compatibility of the evidence with the given hypothesis. The likelihood function is a function of the evidence, E, while the posterior probability is a function of the hypothesis, H. P is sometimes termed the marginal likelihood or "model evidence"; this factor is the same for all possible hypotheses being considered, so this factor does not enter into determining the relative probabilities of different hypotheses. For different values of H, only the factors P and P, both in the numerator, affect the value of P – the posterior probability of a hypothesis is proportional to its prior probability and the newly acquired likelihood.
Bayes' rule can be written as follows: P = P P ⋅ P where the factor P P can be interpreted as the impact of E on the probability of H. Bayesian updating is used and computationally convenient. However, it is not the only updating rule. Ian Hacking noted that traditional "Dutch book" arguments did not specify Bayesian updating: they left open the possibility that non-Bayesian updating rules could avoid Dutch books. Hacking wrote "And neither the Dutch book argument nor any other in the personalist arsenal of proofs of the probability axioms entails the dynamic assumption. Not one entails Bayesianism. So the personalist requires the dynamic assumption to be Bayesian, it is true that in consistency a personalist could abandon the Bayesian model of learning from experience. Salt could lose its savour." Indeed, there are non-Bayesian updating rules that avoid Dutch books following the publication of Richard C. Jeffrey's rule
Supernova
A supernova is an event that occurs upon the death of certain types of stars. Supernovae are more energetic than novae. In Latin, nova means "new", referring astronomically to what appears to be a temporary new bright star. Adding the prefix "super-" distinguishes supernovae from ordinary novae, which are far less luminous; the word supernova was coined by Walter Baade and Fritz Zwicky in 1931. Only three Milky Way, naked-eye supernova events have been observed during the last thousand years, though many have been seen in other galaxies; the most recent directly observed supernova in the Milky Way was Kepler's Supernova in 1604, but two more recent supernova remnants have been found. Statistical observations of supernovae in other galaxies suggest they occur on average about three times every century in the Milky Way, that any galactic supernova would certainly be observable with modern astronomical telescopes. Supernovae may expel much, if not all, of the material away from a star at velocities up to 30,000 km/s or 10% of the speed of light.
This drives an expanding and fast-moving shock wave into the surrounding interstellar medium, in turn, sweeping up an expanding shell of gas and dust, observed as a supernova remnant. Supernovae create and eject the bulk of the chemical elements produced by nucleosynthesis. Supernovae play a significant role in enriching the interstellar medium with the heavier atomic mass chemical elements. Furthermore, the expanding shock waves from supernovae can trigger the formation of new stars. Supernova remnants are expected to accelerate a large fraction of galactic primary cosmic rays, but direct evidence for cosmic ray production was found only in a few of them so far, they are potentially strong galactic sources of gravitational waves. Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first instance, a degenerate white dwarf may accumulate sufficient material from a binary companion, either through accretion or via a merger, to raise its core temperature enough to trigger runaway nuclear fusion disrupting the star.
In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical collapse mechanics have been established and accepted by most astronomers for some time. Owing to the wide range of astrophysical consequences of these events, astronomers now deem supernova research, across the fields of stellar and galactic evolution, as an important area for investigation; the earliest recorded supernova HB9 was viewed by Indians 5,000-years ago and recorded in the oldest Star chart. The SN 185, was viewed by Chinese astronomers in 185 AD; the brightest recorded supernova was SN 1006, which occurred in 1006 AD and was described by observers across China, Iraq and Europe. The observed supernova SN 1054 produced the Crab Nebula. Supernovae SN 1572 and SN 1604, the latest to be observed with the naked eye in the Milky Way galaxy, had notable effects on the development of astronomy in Europe because they were used to argue against the Aristotelian idea that the universe beyond the Moon and planets was static and unchanging.
Johannes Kepler began observing SN 1604 at its peak on October 17, 1604, continued to make estimates of its brightness until it faded from naked eye view a year later. It was the second supernova to be observed in a generation. There is some evidence that the youngest galactic supernova, G1.9+0.3, occurred in the late 19th century more than Cassiopeia A from around 1680. Neither supernova was noted at the time. In the case of G1.9+0.3, high extinction along the plane of the galaxy could have dimmed the event sufficiently to go unnoticed. The situation for Cassiopeia A is less clear. Infrared light echos have been detected showing that it was a type IIb supernova and was not in a region of high extinction. Before the development of the telescope, only five supernovae were seen in the last millennium. Compared to a star's entire history, the visual appearance of a galactic supernova is brief spanning several months, so that the chances of observing one is once in a lifetime. Only a tiny fraction of the 100 billion stars in a typical galaxy have the capacity to become a supernova, restricted to either those having large mass or extraordinarily rare kinds of binary stars containing white dwarfs.
However and discovery of extragalactic supernovae are now far more common. The first such observation was of SN 1885A in the Andromeda galaxy. Today and professional astronomers are finding several hundred every year, some when near maximum brightness, others on old astronomical photographs or plates. American astronomers Rudolph Minkowski and Fritz Zwicky developed the modern supernova classification scheme beginning in 1941. During the 1960s, astronomers found that the maximum intensities of supernovae could be used as standard candles, hence indicators of astronomical distances; some of the most distant supernovae observed in 2003, appeared dimmer than expected. This supports the view. Techniques were developed for reconstructing supernovae events that have no written records of being observed; the date of the Cassiopeia A supernova event was determined from light echoes off nebulae, while the age of supernova remnant RX J0852.0-4622 was estimated from temperature
