The Heavenly Questions or Questions to Heaven is a piece contained in the Classical Chinese poetry collection of Chu Ci, noted both in terms of poetry and as a source for information on the ancient culture of China the area of the ancient state of Chu. Of all the poems attributed to Qu Yuan, "Tianwen" contains more myths than any of the other pieces which may be attributed to him. According to legend, Qu Yuan wrote this series of questions in verse after viewing various scenes depicted on temple murals; the Heavenly Questions consists of a series of verses, in question format, addressed to Tian, or Heaven. The 172 questions asked revolve around Chinese mythology and ancient Chinese religious beliefs, perceived contradictions or conundrums existing therein; that the Tianwen consists in questions rather than answers is somewhat of a problem for mythographers. The questions themselves open up informative windows into a world of ancient mythology; the informational questions raised by Tianwen are a factor that contributes to the description of Tianwen as "the written treasure of Chinese mythology", or as "the most valuable document in Chinese mythology".
The poetic style of the "Heavenly Question" is markedly different from the other sections of the Chuci collection, with the exception of the "Nine Songs". The poetic form of the "Heavenly Questions" is the four-character line, more similar to the Shijing than to the predominantly variable lines typical of the Chuci pieces, the vocabulary is differs from most of the rest of the Chuci, sharing more in common with works in the wisdom tradition like the Daodejing. David Hinton finds that these features of the work suggest that the "Heavenly Questions" has ancient sources in the oral tradition, although having been put together into its present form by Qu Yuan. Hinton finds that much of the power of the poetic impact of the "Heavenly Questions" derives from "its fragmentary and enigmatic character" combined with a pervasive sense of mystery throughout the poem; the content of the "Tianwen" includes questions regarding various myths, which today are important informational sources on the historical development of these myths, with the "Tianwen" representing some of the earliest textual bases of information regarding these myths.
The "Heavenly Questions" was an influence on the works of the Chuci. David Hinton sees the "Heavenly Questions" and the "Nine Songs" as introducing a "shamanistic world from the folk tradition" into the literary tradition of Chinese poetry: appearing in form close to the older, oral tradition in "Heavenly Questions" and the "Nine Songs", these voices from the shamanic world were transformed into poetry of "self-conscious individual authorship" with a personal voice in the "Li Sao". Other examples of the influence of the Heavenly Questions include the poem written by Li He, which A. C. Graham translates as "Don't Go Out of the Door", which in turn influenced the lyrics of the Pink Floyd song "Set the Controls for the Heart of the Sun", attributed to Roger Waters; this translation by Graham features the line: "Witness the man who raved at the wall as he wrote his questions to Heaven". Thus, beginning with the "Heavenly Questions" contained in the Chu Ci anthology of the third or fourth century BCE progressing to the eighth or ninth century work of Li He influenced by Qu Yuan's "Heavenly Questions", continuing on into the twentieth century with Graham's translation, through the subsequent use of this motif by Roger Waters in the lyrics for a song by the popular music band Pink Floyd, subsequently as cover versions of that song in the twenty-first century, "Heavenly Questions" has had a long and enduring influence upon poetry and song.
American poet Gjertrud Schnackenberg used the title Heavenly Questions for her elegy of six linked poems on the death of her husband Robert Nozick in 2002. The work won the Griffin Poetry Prize in 2011; the title was taken from the Chinese poem. Bashe Chu ci List of Chuci contents Liu An Liu Xiang Qu Yuan Song Yu Tian Wang Yi Wu Yinglong Zhulong Birrell, Anne. Chinese Mythology.. ISBN 0-8018-6183-7 Graham, A. C.. Poems of the Late T'ang. New York, New York: The New York Review of Books. ISBN 978-1-59017-257-5 Hawkes, David and introduction. Qu Yuan et al; the Songs of the South: An Ancient Chinese Anthology of Poems by Qu Yuan and Other Poets. London: Penguin Books. ISBN 978-0-14-044375-2 Hinton, David. Classical Chinese Poetry: An Anthology. New York: Farrar and Giroux. ISBN 0-374-10536-7 / ISBN 978-0-374-10536-5. Yang, Lihui, et al.. Handbook of Chinese Mythology. New York: Oxford University Press. ISBN 978-0-19-533263-6 Heavenly Questions by Gjertrud Schnackenberg – review at The Guardian
The Yangtze or Yangzi, 6,300 km long, is the longest river in Asia and the third-longest in the world. The river is the longest in the world to flow within one country, it drains one-fifth of the land area of China, its river basin is home to nearly one-third of the country's population. The Yangtze is the sixth-largest river by discharge volume in the world; the English name Yangtze derives from the Chinese name Yángzǐ Jiāng, which refers to the lowest 435 km of the river between Nanjing and Shanghai. The whole river is known in China as Cháng Jiāng. In more recent modern texts, it is spelled as the Yangzi, in align with its modern pinyin; the Yangtze plays a large role in the history and economy of China. The prosperous Yangtze River Delta generates as much as 20% of the PRC's GDP; the Yangtze River flows through a wide array of ecosystems and is habitat to several endemic and endangered species including the Chinese alligator, the narrow-ridged finless porpoise, the Chinese paddlefish, the Yangtze River dolphin or baiji, the Yangtze sturgeon.
For thousands of years, the river has been used for water, sanitation, industry, boundary-marking and war. The Three Gorges Dam on the Yangtze River is the largest hydro-electric power station in the world. In recent years, the river has suffered from industrial pollution, plastic pollution, agricultural run-off and loss of wetland and lakes, which exacerbates seasonal flooding; some sections of the river are now protected as nature reserves. A stretch of the upstream Yangtze flowing through deep gorges in western Yunnan is part of the Three Parallel Rivers of Yunnan Protected Areas, a UNESCO World Heritage Site. In mid-2014, the Chinese government announced it was building a multi-tier transport network, comprising railways and airports, to create a new economic belt alongside the river; because the source of the Yangtze was not ascertained until modern times, the Chinese have given different names to lower and upstream sections of the river."Yangtze" was the name of Chang Jiang for the lower part from Nanjing to the river mouth at Shanghai.
However, due to the fact that Christian missionaries carried out their activities in this area and were familiar with the name of this part of Chang Jiang, "Yangtze river" was used to refer to the whole Chang Jiang in the English language. In modern Chinese, Yangtze is still used to refer to the lower part of Chang Jiang from Nanjing to the river mouth. Yangtze never stands for the whole Chang Jiang. Chang Jiang is the modern Chinese name for the lower 2,884 km of the Yangtze from its confluence with the Min River at Yibin in Sichuan province to the river mouth at Shanghai. Chang Jiang means the "Long River." In Old Chinese, this stretch of the Yangtze was called Jiang/Kiang 江, a character of phono-semantic compound origin, combining the water radical 氵 with the homophone 工. Krong was a word in the Austroasiatic language of local peoples such as the Yue. Similar to *krong in Proto-Vietnamese and krung in Mon, all meaning "river", it is related to modern Vietnamese sông and Khmer kôngkea. By the Han dynasty, Jiang had come to mean any river in Chinese, this river was distinguished as the "Great River" 大江.
The epithet 長, means "long", was first formally applied to the river during the Six Dynasties period. Various sections of Chang Jiang have local names. From Yibin to Yichang, the river through Sichuan and Chongqing Municipality is known as the Chuan Jiang or "Sichuan River." In Hubei Province, the river is called the Jing Jiang or the "Jing River" after Jingzhou. In Anhui Province, the river takes on the local name Wan Jiang after the shorthand name for Anhui, wǎn, and Yangzi Jiang or the "Yangzi River", from which the English name Yangtze is derived, is the local name for the Lower Yangtze in the region of Yangzhou. The name comes from an ancient ferry crossing called Yangzi or Yangzijin. Europeans who arrived in the Yangtze River Delta region applied this local name to the Å river; the dividing site between upstream and midstream is considered to be at Yichang and that between midstream and downstream at Hukou. The Jinsha River is the name for 2,308 km of the Yangtze from Yibin upstream to the confluence with the Batang River near Yushu in Qinghai Province.
From antiquity until the Ming Dynasty, this stretch of the river was believed to be a tributary of the Yangtze while the Min River was thought to be the main course of the river above Yibin. In the Yu Gong, written in the fifth century BCE, this section is called the Hei Shui 黑水 or the "Black Water." The name "Jinsha" originates in the Song dynasty when the river attracted large numbers of gold prospectors. Gold prospecting along the Jinsha continued to this day. Prior to the Song dynasty, other names were used including, for example Lújiāng from the Three Kingdoms period; the Tongtian River describes the 813 km section from Yushu up to the confluence with the Dangqu River. The name comes from a fabled river in the Journey to the West. In antiquity, it was called the Yak River. In Mongolian, this section is known as the Murui-ussu. and sometimes confused with the nearby Baishui. The Tuotuo River is the official headstream of the Yangtze, a
Flood control methods are used to reduce or prevent the detrimental effects of flood waters. Flood relief methods are used to reduce the effects of high water levels. Floods are caused by many factors or a combination of any of these prolonged heavy rainfall accelerated snowmelt, severe winds over water, unusual high tides, tsunamis, or failure of dams, retention ponds, or other structures that retained the water. Flooding can be exacerbated by increased amounts of impervious surface or by other natural hazards such as wildfires, which reduce the supply of vegetation that can absorb rainfall. Periodic floods occur on many rivers. During times of rain, some of the water is retained in ponds or soil, some is absorbed by grass and vegetation, some evaporates, the rest travels over the land as surface runoff. Floods occur when ponds, riverbeds and vegetation cannot absorb all the water. Water runs off the land in quantities that cannot be carried within stream channels or retained in natural ponds and man-made reservoirs.
About 30 percent of all precipitation becomes runoff and that amount might be increased by water from melting snow. River flooding is caused by heavy rain, sometimes increased by melting snow. A flood that rises with little or no warning, is called a flash flood. Flash floods result from intense rainfall over a small area, or if the area was saturated from previous precipitation; when rainfall is light, the shorelines of lakes and bays can be flooded by severe winds—such as during hurricanes—that blow water into the shore areas. Coastal areas are sometimes flooded by unusually high tides, such as spring tides when compounded by high winds and storm surges. Flooding has many impacts, it endangers the lives of humans and other species. Rapid water runoff causes soil erosion and concomitant sediment deposition elsewhere; the spawning grounds for fish and other wildlife habitats can become polluted or destroyed. Some prolonged high floods can delay traffic in areas. Floods can interfere with drainage and economical use such as interfering with farming.
Structural damage can occur in bridge abutments, bank lines, sewer lines, other structures within floodways. Waterway navigation and hydroelectric power are impaired. Financial losses due to floods are millions of dollars each year, with the worst floods in recent U. S. history having cost billions of dollars. There are many disruptive effects of flooding on economic activities. However, flooding can bring benefits, such as making soil more fertile and providing nutrients in which it is deficient. Periodic flooding was essential to the well-being of ancient communities along the Tigris-Euphrates Rivers, the Nile River, the Indus River, the Ganges and the Yellow River, among others; the viability for hydrologically based renewable sources of energy is higher in flood-prone regions. This is the method used for remote sensing the disasters. Detection of disasters such as floods and explosions are quite complex in previous days and range of detection is inappropriate. But, it came to possibilities by using Multi temporal visualization of Synthetic Aperture Radar images.
But to obtain the good SAR images perfect spatial registration and precise calibration are necessary to specify changes that have occurred. Calibration of SAR is complex and a sensitive problem. Errors may occur after calibration that involves data fusion and visualization process. Traditional image pre-processing cannot be used here due to the on-Gaussian of radar back scattering, but a processing method called "cross calibration/normalization" is used to solve this problem; the application generates a single disaster image called "fast-ready disaster map" from multitemporal SAR images. These maps are generated without user interaction and helps in providing immediate first aid to the people; this process provides image enhancement and comparison between numerous images using data fusion and visualization process. This proposed processing includes histogram truncation and equalization steps; the process helps in identifying the permanent waters and other classes by combined composition of pre-disaster and post-disaster images into a color image for better identity.
Some methods of flood control have been practiced since ancient times. These methods include planting vegetation to retain extra water, terracing hillsides to slow flow downhill, the construction of floodways. Other techniques include the construction of levees, dams, retention ponds to hold extra water during times of flooding. Many dams and their associated reservoirs are designed or to aid in flood protection and control. Many large dams have flood-control reservations in which the level of a reservoir must be kept below a certain elevation before the onset of the rainy/summer melt season to allow a certain amount of space in which floodwaters can fill. Other beneficial uses of dam created reservoirs include hydroelectric power generation, water conservation, recreation. Reservoir and dam construction and design is based upon standards set out by the government. In the United States and reservoir design is regulated by the US Army Corps of Engineers. Design of a dam and reservoir follows guidelines set by the USACE and covers topics such as design flow rates in consideration to meteorological, topographic and soi
Allusion is a figure of speech, in which an object or circumstance from unrelated context is referred to covertly or indirectly. It is left to the audience to make the direct connection. Where the connection is directly and explicitly stated by the author, it is instead termed a reference. In the arts, a literary allusion puts the alluded text in a new context under which it assumes new meanings and denotations, it is not possible to predetermine the nature of all the new meanings and inter-textual patterns that an allusion will generate. Literary allusion is related to parody and pastiche, which are "text-linking" literary devices. In a wider, more informal context, an allusion is a passing or casually short statement indicating broader meaning, it is an incidental mention of something, either directly or by implication, such as "In the stock market, he met his Waterloo." In the most traditional sense, allusion is a literary term, though the word has come to encompass indirect references to any source, including allusions in film or the visual arts.
In literature, allusions are used to link concepts that the reader has knowledge of, with concepts discussed in the story. In the field of film criticism, a film-maker's intentionally unspoken visual reference to another film is called an homage, it may be sensed that real events have allusive overtones, when a previous event is inescapably recalled by a current one. "Allusion is bound up with a vital and perennial topic in literary theory, the place of authorial intention in interpretation", William Irwin observed, in asking "What is an allusion?"Without the hearer or reader's comprehending the author's intention, an allusion becomes a decorative device. Allusion is an economical device, a figure of speech that uses a short space to draw upon the ready stock of ideas, cultural memes or emotion associated with a topic. Thus, an allusion is understandable only to those with prior knowledge of the covert reference in question, a mark of their cultural literacy; the origin of allusion is in the Latin verb ludere, lusus est "to play with, jest."
Recognizing the point of allusion's condensed riddle reinforces cultural solidarity between the maker of the allusion and the hearer: their shared familiarity with allusion bonds them. Ted Cohen finds such a "cultivation of intimacy" to be an essential element of many jokes; some aspect of the referent must be identified for the tacit association to be made. Addressing such issues is an aspect of hermeneutics. William Irwin remarks that allusion moves in only one direction: "If A alludes to B B does not allude to A; the Bible does not allude to Shakespeare, though Shakespeare may allude to the Bible." Irwin appends a note: "Only a divine author, outside of time, would seem capable of alluding to a text." This is the basis for Christian readings of Old Testament prophecy, which asserts that passages are to be read as allusions to future events due to Jesus's revelation in Luke 24:25-27. Allusion differs from the similar term intertextuality in that it is an intentional effort on the author's part.
The success of an allusion depends in part on at least some of its audience "getting" it. Allusions may be made obscure, until at last they are understood by the author alone, who thereby retreats into a private language. In discussing the richly allusive poetry of Virgil's Georgics, R. F. Thomas distinguished six categories of allusive reference, which are applicable to a wider cultural sphere; these types are: Casual Reference, "the use of language which recalls a specific antecedent, but only in a general sense", unimportant to the new context. A type of literature has grown round explorations of the allusions in such works as Alexander Pope's The Rape of the Lock or T. S. Eliot's The Waste Land. In Homer, brief allusions could be made to mythic themes of generations previous to the main narrative because they were familiar to the epic's hearers: one example is the theme of the Calydonian boarhunt. In Hellenistic Alexandria, literary culture and a fixed literary canon known to readers and hearers made a densely allusive poetry effective.
Martin Luther King, Jr. alluded to the Gettysburg Address in starting his "I Have a Dream" speech by saying'Five score years ago...". King's allusion called up parallels in two historic moments without overwhelming his speech with details. A sobriquet is an allusion. By metonymy one aspect of a p
A river is a natural flowing watercourse freshwater, flowing towards an ocean, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, brook and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location. Sometimes a river is defined as being larger than a creek, but not always: the language is vague. Rivers are part of the hydrological cycle. Potamology is the scientific study of rivers, while limnology is the study of inland waters in general. Most of the major cities of the world are situated on the banks of rivers, as they are, or were, used as a source of water, for obtaining food, for transport, as borders, as a defensive measure, as a source of hydropower to drive machinery, for bathing, as a means of disposing of waste.
A river begins at a source, follows a path called a course, ends at a mouth or mouths. The water in a river is confined to a channel, made up of a stream bed between banks. In larger rivers there is also a wider floodplain shaped by flood-waters over-topping the channel. Floodplains may be wide in relation to the size of the river channel; this distinction between river channel and floodplain can be blurred in urban areas where the floodplain of a river channel can become developed by housing and industry. Rivers can flow down mountains, through valleys or along plains, can create canyons or gorges; the term upriver refers to the direction towards the source of the river, i.e. against the direction of flow. The term downriver describes the direction towards the mouth of the river, in which the current flows; the term left bank refers to the left bank in the direction of right bank to the right. The river channel contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river.
Extensive braided rivers are now found in only a few regions worldwide, such as the South Island of New Zealand. They occur on peneplains and some of the larger river deltas. Anastamosing rivers are quite rare, they have multiple sinuous channels carrying large volumes of sediment. There are rare cases of river bifurcation in which a river divides and the resultant flows ending in different seas. An example is the bifurcation of Nerodime River in Kosovo. A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. In 1757, the German hydrologist Albert Brahms empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed; this formulation is sometimes called Airy's law. Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks.
A river valley, created from a U-shaped glaciated valley, can easily be identified by the V-shaped channel that it has carved. In the middle reaches where a river flows over flatter land, meanders may form through erosion of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake or billabong. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths. Rivers whose mouths are in saline tidal waters may form estuaries. Throughout the course of the river, the total volume of water transported downstream will be a combination of the free water flow together with a substantial volume flowing through sub-surface rocks and gravels that underlie the river and its floodplain. For many rivers in large valleys, this unseen component of flow may exceed the visible flow. Most but not all rivers flow on the surface. Subterranean rivers flow underground in caverns; such rivers are found in regions with limestone geologic formations.
Subglacial streams are the braided rivers that flow at the beds of glaciers and ice sheets, permitting meltwater to be discharged at the front of the glacier. Because of the gradient in pressure due to the overlying weight of the glacier, such streams can flow uphill. An intermittent river only flows and can be dry for several years at a time; these rivers are found in regions with limited or variable rainfall, or can occur because of geologic conditions such as a permeable river bed. Some ephemeral rivers flow during the summer months but not in the winter; such rivers are fed from chalk aquifers which recharge from winter rainfall. In England these rivers are called bournes and give their name to places such as Bournemouth and Eastbourne. In humid regions, the location where flow begins in the smallest tributary streams moves upstream in response to precipitation and downstream in its absence or when active summer vegetation diverts water for evapotrans
Yu the Great
Yu the Great, born Si Wenming, was a legendary ruler in ancient China famed for his introduction of flood control, inaugurating dynastic rule in China by establishing the Xia dynasty, for his upright moral character. The dates proposed for Yu's reign predate the oldest-known written records in China, the oracle bones of the late Shang dynasty, by nearly a millennium. No inscriptions on artifacts from the proposed era of Yu, nor the oracle bones, make any mention of Yu; the lack of anything remotely close to contemporary documentary evidence has led to some controversy over the historicity of Yu. Proponents of the historicity of Yu theorise that stories about his life and reign were transmitted orally in various areas of China until they were recorded in the Zhou dynasty, while opponents believe the figure existed in legend in a different form—as a god or mythical animal—in the Xia dynasty, morphed into a human figure by the start of the Zhou dynasty. Many of the stories about Yu were collected in Sima Qian's famous Records of the Grand Historian.
Yu and other "sage-kings" of Ancient China were lauded for their virtues and morals by Confucius and other Chinese teachers. Yu is one of the few Chinese rulers posthumously honored with the epithet "the Great". According to several ancient Chinese records, Yu was the eight-times-great-grandson of the Yellow Emperor: Yu's father, was the five-times-great-grandson of Emperor Zhuanxu. Yu was said to have been born at Mount Wen, in modern-day Beichuan County, Sichuan Province, though there are debates as to whether he was born in Shifang instead. Yu's mother was of the Youxin clan named either Nüxi; when Yu was a child, his father Gun moved the people east toward the Central Plain. King Yao enfeoffed Gun as lord of Chong identified as the middle peak of Mount Song. Yu is thus believed to have grown up on the slopes of Mount Song, just south of the Yellow River, he married a woman from Mount Tu, referred to as Tushan-shi. They had a son named Qi, a name meaning "revelation"; the location of Mount Tu has always been disputed.
The two most probable locations are Mount Tu in Anhui Province and the Tu Peak of the Southern Mountain in Chongqing Municipality. During the reign of king Yao, the Chinese heartland was plagued by floods that prevented further economic and social development. Yu's father, was tasked with devising a system to control the flooding, he spent more than nine years building a series of dikes and dams along the riverbanks, but all of this was ineffective, despite the great number and size of these dikes and the use of a special self-expanding soil. As an adult, Yu continued his father's work and made a careful study of the river systems in an attempt to learn why his father's great efforts had failed. Collaborating with Hou Ji, a semi-mythical agricultural master about whom little is concretely known, Yu devised a system of flood controls that were crucial in establishing the prosperity of the Chinese heartland. Instead of directly damming the rivers' flow, Yu made a system of irrigation canals which relieved floodwater into fields, as well as spending great effort dredging the riverbeds.
Yu is said to have eaten and slept with the common workers and spent most of his time assisting the work of dredging the silty beds of the rivers for the thirteen years the projects took to complete. The dredging and irrigation were successful, allowed ancient Chinese culture to flourish along the Yellow River, Wei River, other waterways of the Chinese heartland; the project earned Yu renown throughout Chinese history, is referred to in Chinese history as "Great Yu Controls the Waters". In particular, Mount Longmen along the Yellow River had a narrow channel which blocked water from flowing east toward the ocean. Yu is said to have brought a large number of workers to open up this channel, known since as "Yu's Gateway". In a mythical version of this story, presented in Wang Jia's 4th-century AD work Shi Yi Ji, Yu is assisted in his work by a yellow dragon and a black turtle. Another local myth says that Yu created the Sanmenxia "Three Passes Gorge" of the Yangzi River by cutting a mountain ridge with a divine battle-axe to control flooding.
Traditional stories say. For example, his hands were said to be thickly callused, his feet were covered with callus. In one common story, Yu had only been married four days when he was given the task of fighting the flood, he said goodbye to his wife. During the thirteen years of flooding, he passed by his own family's doorstep three times, but each time he did not return inside his own home; the first time he passed, he heard. The second time he passed by, his son could call out to his father, his family urged him to return home. The third time Yu was passing by, his son was older than ten years old; each time, Yu refused to go in the door, saying that as the flood was rendering countless number of people homeless, he could not rest. Yu killed Gonggong's minister Xiangliu, a nine-headed snake monster. King Shun, who reigned after Yao, was so impressed by Yu's engineering work and diligence that
Cosmology is a branch of astronomy concerned with the studies of the origin and evolution of the universe, from the Big Bang to today and on into the future. It is the scientific study of the origin and eventual fate of the universe. Physical cosmology is the scientific study of the universe's origin, its large-scale structures and dynamics, its ultimate fate, as well as the laws of science that govern these areas; the term cosmology was first used in English in 1656 in Thomas Blount's Glossographia, in 1731 taken up in Latin by German philosopher Christian Wolff, in Cosmologia Generalis. Religious or mythological cosmology is a body of beliefs based on mythological and esoteric literature and traditions of creation myths and eschatology. Physical cosmology is studied by scientists, such as astronomers and physicists, as well as philosophers, such as metaphysicians, philosophers of physics, philosophers of space and time; because of this shared scope with philosophy, theories in physical cosmology may include both scientific and non-scientific propositions, may depend upon assumptions that cannot be tested.
Cosmology differs from astronomy in that the former is concerned with the Universe as a whole while the latter deals with individual celestial objects. Modern physical cosmology is dominated by the Big Bang theory, which attempts to bring together observational astronomy and particle physics. Theoretical astrophysicist David N. Spergel has described cosmology as a "historical science" because "when we look out in space, we look back in time" due to the finite nature of the speed of light. Physics and astrophysics have played a central role in shaping the understanding of the universe through scientific observation and experiment. Physical cosmology was shaped through both mathematics and observation in an analysis of the whole universe; the universe is understood to have begun with the Big Bang, followed instantaneously by cosmic inflation. Cosmogony studies the origin of the Universe, cosmography maps the features of the Universe. In Diderot's Encyclopédie, cosmology is broken down into uranology, aerology and hydrology.
Metaphysical cosmology has been described as the placing of humans in the universe in relationship to all other entities. This is exemplified by Marcus Aurelius's observation that a man's place in that relationship: "He who does not know what the world is does not know where he is, he who does not know for what purpose the world exists, does not know who he is, nor what the world is." Physical cosmology is the branch of physics and astrophysics that deals with the study of the physical origins and evolution of the Universe. It includes the study of the nature of the Universe on a large scale. In its earliest form, it was, the study of the heavens. Greek philosophers Aristarchus of Samos and Ptolemy proposed different cosmological theories; the geocentric Ptolemaic system was the prevailing theory until the 16th century when Nicolaus Copernicus, subsequently Johannes Kepler and Galileo Galilei, proposed a heliocentric system. This is one of the most famous examples of epistemological rupture in physical cosmology.
Isaac Newton's Principia Mathematica, published in 1687, was the first description of the law of universal gravitation. It provided a physical mechanism for Kepler's laws and allowed the anomalies in previous systems, caused by gravitational interaction between the planets, to be resolved. A fundamental difference between Newton's cosmology and those preceding it was the Copernican principle—that the bodies on earth obey the same physical laws as all the celestial bodies; this was a crucial philosophical advance in physical cosmology. Modern scientific cosmology is considered to have begun in 1917 with Albert Einstein's publication of his final modification of general relativity in the paper "Cosmological Considerations of the General Theory of Relativity". General relativity prompted cosmogonists such as Willem de Sitter, Karl Schwarzschild, Arthur Eddington to explore its astronomical ramifications, which enhanced the ability of astronomers to study distant objects. Physicists unchanging. In 1922 Alexander Friedmann introduced the idea of an expanding universe that contained moving matter.
Around the same time the Great Debate took place, with early cosmologists such as Heber Curtis and Ernst Öpik determining that some nebulae seen in telescopes were separate galaxies far distant from our own. In parallel to this dynamic approach to cosmology, one long-standing debate about the structure of the cosmos was coming to a climax. Mount Wilson astronomer Harlow Shapley championed the model of a cosmos made up of the Milky Way star system only; this difference of ideas came to a climax with the organization of the Great Debate on 26 April 1920 at the meeting of the U. S. National Academy of Sciences in Washington, D. C; the debate was resolved when Edwin Hubble detected Cepheid Variables in the Andromeda galaxy in 1923 and 1924. Their distance established spiral nebulae well beyond the edge of the Milky Way. S