156-469: The history of astronomy focuses on the contributions civilizations have made to further their understanding of the universe beyond earth's atmosphere. Astronomy is one of the oldest natural sciences , achieving a high level of success in the second half of the first millennium. Astronomy has origins in the religious , mythological , cosmological , calendrical, and astrological beliefs and practices of prehistory. Early astronomical records date back to
312-558: A Hubble sphere . Some disputed estimates for the total size of the universe, if finite, reach as high as 10 10 10 122 {\displaystyle 10^{10^{10^{122}}}} megaparsecs, as implied by a suggested resolution of the No-Boundary Proposal . Assuming that the Lambda-CDM model is correct, the measurements of the parameters using a variety of techniques by numerous experiments yield
468-581: A slippery slope scenario in his style guide that, "if we do end by casting aside the AD/BC convention, almost certainly some will argue that we ought to cast aside as well the conventional numbering system [that is, the method of numbering years] itself, given its Christian basis." Some Christians are offended by the removal of the reference to Jesus, including the Southern Baptist Convention . The abbreviation BCE, just as with BC, always follows
624-400: A water clock , gnomon , shadows, and intercalations . The Babylonian GU text arranges stars in 'strings' that lie along declination circles and thus measure right-ascensions or time-intervals, and also employs the stars of the zenith, which are also separated by given right-ascensional differences. A significant increase in the quality and frequency of Babylonian observations appeared during
780-462: A best value of the age of the universe at 13.799 ± 0.021 billion years, as of 2015. Over time, the universe and its contents have evolved. For example, the relative population of quasars and galaxies has changed and the universe has expanded . This expansion is inferred from the observation that the light from distant galaxies has been redshifted , which implies that the galaxies are receding from us. Analyses of Type Ia supernovae indicate that
936-600: A computational system based on a planetary model in which the Earth was taken to be spinning on its axis and the periods of the planets were given with respect to the Sun. He accurately calculated many astronomical constants, such as the periods of the planets, times of the solar and lunar eclipses , and the instantaneous motion of the Moon. Early followers of Aryabhata's model included Varāhamihira , Brahmagupta , and Bhāskara II . Astronomy
1092-442: A detailed description of the temporary star. In the late 10th century, a huge observatory was built near Tehran , Iran , by the astronomer Abu-Mahmud al-Khujandi who observed a series of meridian transits of the Sun, which allowed him to calculate the tilt of the Earth's axis relative to the Sun. He noted that measurements by earlier (Indian, then Greek) astronomers had found higher values for this angle, possible evidence that
1248-402: A galaxy have planets . At the largest scale , galaxies are distributed uniformly and the same in all directions, meaning that the universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure. Discoveries in the early 20th century have suggested that
1404-630: A generic sense, to refer to "the common era of the Jews". The first use of the phrase "before the common era" may be that in a 1770 work that also uses common era and vulgar era as synonyms, in a translation of a book originally written in German. The 1797 edition of the Encyclopædia Britannica uses the terms vulgar era and common era synonymously. In 1835, in his book Living Oracles , Alexander Campbell , wrote: "The vulgar Era, or Anno Domini;
1560-540: A lasting effect on astronomy up to the Renaissance . In his Planetary Hypotheses , Ptolemy ventured into the realm of cosmology, developing a physical model of his geometric system, in a universe many times smaller than the more realistic conception of Aristarchus of Samos four centuries earlier. The precise orientation of the Egyptian pyramids affords a lasting demonstration of the high degree of technical skill in watching
1716-602: A matter of convenience. There is so much interaction between people of different faiths and cultures – different civilizations, if you like – that some shared way of reckoning time is a necessity. And so the Christian Era has become the Common Era. Adena K. Berkowitz, in her application to argue before the United States Supreme Court , opted to use BCE and CE because, "Given the multicultural society that we live in,
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#17329202097321872-502: A method by which monks could determine the time of prayer at night by watching the stars. In the 7th century the English monk Bede of Jarrow published an influential text, On the Reckoning of Time , providing churchmen with the practical astronomical knowledge needed to compute the proper date of Easter using a procedure called the computus . This text remained an important element of
2028-685: A period of 138 years in which the traditional BC/AD dating notation was used. BCE/CE is used by the College Board in its history tests, and by the Norton Anthology of English Literature . Others have taken a different approach. The US-based History Channel uses BCE/CE notation in articles on non-Christian religious topics such as Jerusalem and Judaism . The 2006 style guide for the Episcopal Diocese Maryland Church News says that BCE and CE should be used. In June 2006, in
2184-532: A precise description of the eclipses as depicted in the Dresden Codex , as well as the ecliptic or zodiac, and the Milky Way was crucial in their Cosmology. A number of important Maya structures are believed to have been oriented toward the extreme risings and settings of Venus. To the ancient Maya, Venus was the patron of war and many recorded battles are believed to have been timed to the motions of this planet. Mars
2340-539: A reasonably good account of various observations about the universe. The initial hot, dense state is called the Planck epoch , a brief period extending from time zero to one Planck time unit of approximately 10 seconds. During the Planck epoch, all types of matter and all types of energy were concentrated into a dense state, and gravity —currently the weakest by far of the four known forces —is believed to have been as strong as
2496-442: A set of four coordinates: ( x , y , z , t ) . On average, space is observed to be very nearly flat (with a curvature close to zero), meaning that Euclidean geometry is empirically true with high accuracy throughout most of the universe. Spacetime also appears to have a simply connected topology , in analogy with a sphere, at least on the length scale of the observable universe. However, present observations cannot exclude
2652-509: A sophisticated knowledge of mathematics and astronomy. Among the discoveries are: The origins of astronomy can be found in Mesopotamia , the "land between the rivers" Tigris and Euphrates , where the ancient kingdoms of Sumer , Assyria , and Babylonia were located. A form of writing known as cuneiform emerged among the Sumerians around 3500–3000 BC. Our knowledge of Sumerian astronomy
2808-593: A tyrant who persecuted Christians. He numbered years from an initial reference date (" epoch "), an event he referred to as the Incarnation of Jesus. Dionysius labeled the column of the table in which he introduced the new era as " Anni Domini Nostri Jesu Christi " (Of the year of our Lord Jesus Christ]. This way of numbering years became more widespread in Europe with its use by Bede in England in 731. Bede also introduced
2964-538: Is Tablet 63 of the Enūma Anu Enlil , the Venus tablet of Ammi-saduqa , which lists the first and last visible risings of Venus over a period of about 21 years and is the earliest evidence that the phenomena of a planet were recognized as periodic. The MUL.APIN , contains catalogues of stars and constellations as well as schemes for predicting heliacal risings and the settings of the planets, lengths of daylight measured by
3120-445: Is a composite particle made of quarks held together by the strong force . Hadrons are categorized into two families: baryons (such as protons and neutrons ) made of three quarks, and mesons (such as pions ) made of one quark and one antiquark . Of the hadrons, protons are stable, and neutrons bound within atomic nuclei are stable. Other hadrons are unstable under ordinary conditions and are thus insignificant constituents of
3276-480: Is a direct reference to Jesus as Lord . Proponents of the Common Era notation assert that the use of BCE/CE shows sensitivity to those who use the same year numbering system as the one that originated with and is currently used by Christians , but who are not themselves Christian. Former United Nations Secretary-General Kofi Annan has argued: [T]he Christian calendar no longer belongs exclusively to Christians. People of all faiths have taken to using it simply as
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#17329202097323432-563: Is also mentioned in preserved astronomical codices and early mythology . Although the Maya calendar was not tied to the Sun, John Teeple has proposed that the Maya calculated the solar year to somewhat greater accuracy than the Gregorian calendar . Both astronomy and an intricate numerological scheme for the measurement of time were vitally important components of Maya religion . The Maya believed that
3588-648: Is available in two recensions, one belonging to the Rig Veda, and the other to the Yajur Veda. According to the Vedanga Jyotisha, in a yuga or "era", there are 5 solar years, 67 lunar sidereal cycles, 1,830 days, 1,835 sidereal days and 62 synodic months. During the 6th century, astronomy was influenced by the Greek and Byzantine astronomical traditions. Aryabhata (476–550), in his magnum opus Aryabhatiya (499), propounded
3744-417: Is called the observable universe . The proper distance (measured at a fixed time) between Earth and the edge of the observable universe is 46 billion light-years (14 billion parsecs ), making the diameter of the observable universe about 93 billion light-years (28 billion parsecs). Although the distance traveled by light from the edge of the observable universe is close to the age of the universe times
3900-411: Is composed almost completely of dark energy, dark matter, and ordinary matter . Other contents are electromagnetic radiation (estimated to constitute from 0.005% to close to 0.01% of the total mass–energy of the universe) and antimatter . The proportions of all types of matter and energy have changed over the history of the universe. The total amount of electromagnetic radiation generated within
4056-405: Is composed of two types of elementary particles : quarks and leptons . For example, the proton is formed of two up quarks and one down quark ; the neutron is formed of two down quarks and one up quark; and the electron is a kind of lepton. An atom consists of an atomic nucleus , made up of protons and neutrons (both of which are baryons ), and electrons that orbit the nucleus. Soon after
4212-646: Is equal to, less than, or greater than 1. These are called, respectively, the flat, open and closed universes. Observations, including the Cosmic Background Explorer (COBE), Wilkinson Microwave Anisotropy Probe (WMAP), and Planck maps of the CMB, suggest that the universe is infinite in extent with a finite age, as described by the Friedmann–Lemaître–Robertson–Walker (FLRW) models. These FLRW models thus support inflationary models and
4368-511: Is found in atoms and is directly tied to all chemical properties . Neutrinos rarely interact with anything, and are consequently rarely observed. Neutrinos stream throughout the universe but rarely interact with normal matter. BCE Common Era ( CE ) and Before the Common Era ( BCE ) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar ), the world's most widely used calendar era . Common Era and Before
4524-402: Is generally believed that the first astronomers were priests , and that they understood celestial objects and events to be manifestations of the divine , hence early astronomy's connection to what is now called astrology . A 32,500-year-old carved ivory mammoth tusk could contain the oldest known star chart (resembling the constellation Orion ). It has also been suggested that drawings on
4680-481: Is in particularly common use in Nepal in order to disambiguate dates from the local calendar, Bikram or Vikram Sambat. Disambiguation is needed because the era of the local calendar is quite close to the Common Era. In 2002, an advisory panel for the religious education syllabus for England and Wales recommended introducing BCE/CE dates to schools, and by 2018 some local education authorities were using them. In 2018,
4836-597: Is in the Local Group of galaxies, which in turn is in the Laniakea Supercluster . This supercluster spans over 500 million light-years, while the Local Group spans over 10 million light-years. The universe also has vast regions of relative emptiness; the largest known void measures 1.8 billion ly (550 Mpc) across. The observable universe is isotropic on scales significantly larger than superclusters, meaning that
History of astronomy - Misplaced Pages Continue
4992-630: Is indirect, via the earliest Babylonian star catalogues dating from about 1200 BC. The fact that many star names appear in Sumerian suggests a continuity reaching into the Early Bronze Age. Astral theology , which gave planetary gods an important role in Mesopotamian mythology and religion , began with the Sumerians . They also used a sexagesimal (base 60) place-value number system, which simplified
5148-523: Is known as dark matter . In the widely accepted ΛCDM cosmological model, dark matter accounts for about 25.8% ± 1.1% of the mass and energy in the universe while about 69.2% ± 1.2% is dark energy , a mysterious form of energy responsible for the acceleration of the expansion of the universe . Ordinary (' baryonic ') matter therefore composes only 4.84% ± 0.1% of the universe. Stars, planets, and visible gas clouds only form about 6% of this ordinary matter. There are many competing hypotheses about
5304-782: Is subject to the Pauli exclusion principle ; no two leptons of the same species can be in exactly the same state at the same time. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos ). Electrons are stable and the most common charged lepton in the universe, whereas muons and taus are unstable particles that quickly decay after being produced in high energy collisions, such as those involving cosmic rays or carried out in particle accelerators . Charged leptons can combine with other particles to form various composite particles such as atoms and positronium . The electron governs nearly all of chemistry , as it
5460-480: Is the Standard Model , a theory that is concerned with electromagnetic interactions and the weak and strong nuclear interactions. The Standard Model is supported by the experimental confirmation of the existence of particles that compose matter: quarks and leptons , and their corresponding " antimatter " duals, as well as the force particles that mediate interactions : the photon , the W and Z bosons , and
5616-430: Is unknown whether or not they are composed of smaller and even more fundamental particles. In most contemporary models they are thought of as points in space. All elementary particles are currently best explained by quantum mechanics and exhibit wave–particle duality : their behavior has both particle-like and wave -like aspects, with different features dominating under different circumstances. Of central importance
5772-869: Is unknown. Dark matter, a mysterious form of matter that has not yet been identified, accounts for 26.8% of the cosmic contents. Dark energy, which is the energy of empty space and is causing the expansion of the universe to accelerate, accounts for the remaining 68.3% of the contents. Matter, dark matter, and dark energy are distributed homogeneously throughout the universe over length scales longer than 300 million light-years (ly) or so. However, over shorter length-scales, matter tends to clump hierarchically; many atoms are condensed into stars , most stars into galaxies, most galaxies into clusters, superclusters and, finally, large-scale galactic filaments . The observable universe contains as many as an estimated 2 trillion galaxies and, overall, as many as an estimated 10 stars – more stars (and earth-like planets) than all
5928-572: The Andromeda Galaxy . He mentions it as lying before the mouth of a Big Fish, an Arabic constellation . This "cloud" was apparently commonly known to the Isfahan astronomers, very probably before 905 AD. The first recorded mention of the Large Magellanic Cloud was also given by al-Sufi. In 1006, Ali ibn Ridwan observed SN 1006 , the brightest supernova in recorded history, and left
6084-462: The Babylonians around 1000 BCE. There is also astronomical evidence of interest from early Chinese, Central American and North European cultures. Astronomy was used by early cultures for a variety of reasons. These include timekeeping, navigation , spiritual and religious practices, and agricultural planning. Ancient astronomers used their observations to chart the skies in an effort to learn about
6240-516: The Berlin Museum ; a short handle from which a plumb line was hung, and a palm branch with a sight-slit in the broader end. The latter was held close to the eye, the former in the other hand, perhaps at arm's length. The "Hermetic" books which Clement refers to are the Egyptian theological texts, which probably have nothing to do with Hellenistic Hermetism . From the tables of stars on the ceiling of
6396-576: The Big Bang , primordial protons and neutrons formed from the quark–gluon plasma of the early universe as it cooled below two trillion degrees. A few minutes later, in a process known as Big Bang nucleosynthesis , nuclei formed from the primordial protons and neutrons. This nucleosynthesis formed lighter elements, those with small atomic numbers up to lithium and beryllium , but the abundance of heavier elements dropped off sharply with increasing atomic number. Some boron may have been formed at this time, but
History of astronomy - Misplaced Pages Continue
6552-418: The Big Bang , would have completely annihilated each other and left only photons as a result of their interaction. These laws are Gauss's law and the non-divergence of the stress–energy–momentum pseudotensor . Due to the finite speed of light , there is a limit (known as the particle horizon ) to how far light can travel over the age of the universe . The spatial region from which we can receive light
6708-482: The German words Das All , Weltall , and Natur for universe . The same synonyms are found in English, such as everything (as in the theory of everything ), the cosmos (as in cosmology ), the world (as in the many-worlds interpretation ), and nature (as in natural laws or natural philosophy ). The prevailing model for the evolution of the universe is the Big Bang theory. The Big Bang model states that
6864-591: The Gregorian calendar without the AD prefix. As early as 1825, the abbreviation VE (for Vulgar Era) was in use among Jews to denote years in the Western calendar. As of 2005 , Common Era notation has also been in use for Hebrew lessons for more than a century. Jews have also used the term Current Era . Some academics in the fields of theology , education , archaeology and history have adopted CE and BCE notation despite some disagreement. A study conducted in 2014 found that
7020-489: The Hermetic astrological books, which are four in number. Of these, one is about the arrangement of the fixed stars that are visible; one on the positions of the Sun and Moon and five planets; one on the conjunctions and phases of the Sun and Moon; and one concerns their risings. The Astrologer's instruments ( horologium and palm ) are a plumb line and sighting instrument. They have been identified with two inscribed objects in
7176-508: The Milky Way is roughly 100,000–180,000 light-years in diameter, and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy , is located roughly 2.5 million light-years away. Because humans cannot observe space beyond the edge of the observable universe, it is unknown whether the size of the universe in its totality is finite or infinite. Estimates suggest that the whole universe, if finite, must be more than 250 times larger than
7332-546: The National Archaeological Museum of Athens , accompanied by a replica. Depending on the historian's viewpoint, the acme or corruption of Classical physical astronomy is seen with Ptolemy , a Greco-Roman astronomer from Alexandria of Egypt, who wrote the classic comprehensive presentation of geocentric astronomy, the Megale Syntaxis (Great Synthesis), better known by its Arabic title Almagest , which had
7488-704: The National Trust said it would continue to use BC/AD as its house style. English Heritage explains its era policy thus: "It might seem strange to use a Christian calendar system when referring to British prehistory, but the BC/AD labels are widely used and understood." Some parts of the BBC use BCE/CE, but some presenters have said they will not. As of October 2019, the BBC News style guide has entries for AD and BC, but not for CE or BCE. The style guide for The Guardian says, under
7644-597: The date of birth of Jesus . Since the year numbers are the same, BCE and CE dates should be equally offensive to other religions as BC and AD. Roman Catholic priest and writer on interfaith issues Raimon Panikkar argued that the BCE/CE usage is the less inclusive option since they are still using the Christian calendar numbers and forcing it on other nations. In 1993, the English-language expert Kenneth G. Wilson speculated
7800-463: The expansion is accelerating . The more matter there is in the universe, the stronger the mutual gravitational pull of the matter. If the universe were too dense then it would re-collapse into a gravitational singularity . However, if the universe contained too little matter then the self-gravity would be too weak for astronomical structures, like galaxies or planets, to form. Since the Big Bang,
7956-631: The fixed stars . They were the first to record a supernova, in the Astrological Annals of the Houhanshu in 185 AD. Also, the supernova that created the Crab Nebula in 1054 is an example of a "guest star" observed by Chinese astronomers, although it was not recorded by their European contemporaries. Ancient astronomical records of phenomena like supernovae and comets are sometimes used in modern astronomical studies. The world's first star catalogue
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#17329202097328112-404: The general theory of relativity , explains gravity by recognizing that spacetime is not fixed but instead dynamical. In general relativity, gravitational force is reimagined as curvature of spacetime . A curved path like an orbit is not the result of a force deflecting a body from an ideal straight-line path, but rather the body's attempt to fall freely through a background that is itself curved by
8268-553: The gluon . The Standard Model predicted the existence of the recently discovered Higgs boson , a particle that is a manifestation of a field within the universe that can endow particles with mass. Because of its success in explaining a wide variety of experimental results, the Standard Model is sometimes regarded as a "theory of almost everything". The Standard Model does not, however, accommodate gravity. A true force–particle "theory of everything" has not been attained. A hadron
8424-483: The grains of beach sand on planet Earth ; but less than the total number of atoms estimated in the universe as 10 ; and the estimated total number of stars in an inflationary universe (observed and unobserved), as 10 . Typical galaxies range from dwarfs with as few as ten million (10 ) stars up to giants with one trillion (10 ) stars. Between the larger structures are voids , which are typically 10–150 Mpc (33 million–490 million ly) in diameter. The Milky Way
8580-441: The hadron epoch , and the lepton epoch . Together, these epochs encompassed less than 10 seconds of time following the Big Bang. These elementary particles associated stably into ever larger combinations, including stable protons and neutrons , which then formed more complex atomic nuclei through nuclear fusion . This process, known as Big Bang nucleosynthesis , lasted for about 17 minutes and ended about 20 minutes after
8736-404: The large-scale structure of the universe. Other than neutrinos , a form of hot dark matter , dark matter has not been detected directly, making it one of the greatest mysteries in modern astrophysics . Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level. Dark matter is estimated to constitute 26.8% of the total mass–energy and 84.5% of
8892-399: The law of universal gravitation , Isaac Newton built upon Copernicus's work as well as Johannes Kepler 's laws of planetary motion and observations by Tycho Brahe . Further observational improvements led to the realization that the Sun is one of a few hundred billion stars in the Milky Way , which is one of a few hundred billion galaxies in the observable universe. Many of the stars in
9048-421: The observable universe and global geometry . Cosmologists often work with a given space-like slice of spacetime called the comoving coordinates . The section of spacetime which can be observed is the backward light cone , which delimits the cosmological horizon . The cosmological horizon, also called the particle horizon or the light horizon, is the maximum distance from which particles can have traveled to
9204-442: The observer in the age of the universe . This horizon represents the boundary between the observable and the unobservable regions of the universe. An important parameter determining the future evolution of the universe theory is the density parameter , Omega (Ω), defined as the average matter density of the universe divided by a critical value of that density. This selects one of three possible geometries depending on whether Ω
9360-624: The ultimate fate of the universe and about what, if anything, preceded the Big Bang, while other physicists and philosophers refuse to speculate, doubting that information about prior states will ever be accessible. Some physicists have suggested various multiverse hypotheses, in which the universe might be one among many. The physical universe is defined as all of space and time (collectively referred to as spacetime ) and their contents. Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter , and therefore planets, moons , stars, galaxies, and
9516-477: The weak and strong nuclear forces , decline very rapidly with distance; their effects are confined mainly to sub-atomic length scales. The universe appears to have much more matter than antimatter , an asymmetry possibly related to the CP violation . This imbalance between matter and antimatter is partially responsible for the existence of all matter existing today, since matter and antimatter, if equally produced at
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#17329202097329672-437: The 10th century, Albumasar's "Introduction" was one of the most important sources for the recovery of Aristotle for medieval European scholars. Abd al-Rahman al-Sufi (Azophi) carried out observations on the stars and described their positions, magnitudes , brightness, and colour and drawings for each constellation in his Book of Fixed Stars . He also gave the first descriptions and pictures of "A Little Cloud" now known as
9828-566: The 16th century. Nilakantha Somayaji, in his Aryabhatiyabhasya , a commentary on Aryabhata's Aryabhatiya , developed his own computational system for a partially heliocentric planetary model, in which Mercury, Venus, Mars , Jupiter and Saturn orbit the Sun , which in turn orbits the Earth , similar to the Tychonic system later proposed by Tycho Brahe in the late 16th century. Nilakantha's system, however,
9984-581: The BCE/CE notation is not growing at the expense of BC and AD notation in the scholarly literature, and that both notations are used in a relatively stable fashion. In 2011, media reports suggested that the BC/AD notation in Australian school textbooks would be replaced by BCE/CE notation. The change drew opposition from some politicians and church leaders. Weeks after the story broke, the Australian Curriculum, Assessment and Reporting Authority denied
10140-421: The Big Bang, so only the fastest and simplest reactions occurred. About 25% of the protons and all the neutrons in the universe, by mass, were converted to helium , with small amounts of deuterium (a form of hydrogen ) and traces of lithium . Any other element was only formed in very tiny quantities. The other 75% of the protons remained unaffected, as hydrogen nuclei. After nucleosynthesis ended,
10296-568: The Christian Era, it was sometimes qualified, e.g., "common era of the Incarnation", "common era of the Nativity", or "common era of the birth of Christ". An adapted translation of Common Era into Latin as Era Vulgaris was adopted in the 20th century by some followers of Aleister Crowley , and thus the abbreviation "e.v." or "EV" may sometimes be seen as a replacement for AD. Although Jews have their own Hebrew calendar , they often use
10452-652: The Common Era are alternatives to the original Anno Domini (AD) and Before Christ (BC) notations used for the same calendar era. The two notation systems are numerically equivalent: "2024 CE" and "AD 2024" each describe the current year; "400 BCE" and "400 BC" are the same year. The expression can be traced back to 1615, when it first appears in a book by Johannes Kepler as the Latin : annus aerae nostrae vulgaris ( year of our common era ), and to 1635 in English as " Vulgar Era". The term "Common Era" can be found in English as early as 1708, and became more widely used in
10608-620: The Earth was the center of all things, and that the stars, moons, and planets were gods. They believed that their movements were the gods traveling between the Earth and other celestial destinations. Many key events in Maya culture were timed around celestial events, in the belief that certain gods would be present. The Arabic and the Persian world under Islam had become highly cultured, and many important works of knowledge from Greek astronomy and Indian astronomy and Persian astronomy were translated into Arabic, used and stored in libraries throughout
10764-412: The Earth. This basic cosmological model prevailed, in various forms, until the 16th century. In the 3rd century BC Aristarchus of Samos was the first to suggest a heliocentric system, although only fragmentary descriptions of his idea survive. Eratosthenes estimated the circumference of the Earth with great accuracy (see also: history of geodesy ). Greek geometrical astronomy developed away from
10920-487: The Gregorian Calendar as BCE and CE without compromising their own beliefs about the divinity of Jesus of Nazareth." In History Today , Michael Ostling wrote: "BC/AD Dating: In the year of whose Lord? The continuing use of AD and BC is not only factually wrong but also offensive to many who are not Christians." Critics note the fact that there is no difference in the epoch of the two systems—chosen to be close to
11076-573: The Roman era through the 12th century. This lack of progress has led some astronomers to assert that nothing happened in Western European astronomy during the Middle Ages. Recent investigations, however, have revealed a more complex picture of the study and teaching of astronomy in the period from the 4th to the 16th centuries. Western Europe entered the Middle Ages with great difficulties that affected
11232-459: The Sun and Moon (marking the day , month and year ), and were important to agricultural societies, in which the harvest depended on planting at the correct time of year, and for which the nearly full moon was the only lighting for night-time travel into city markets. The common modern calendar is based on the Roman calendar . Although originally a lunar calendar , it broke the traditional link of
11388-603: The United States, the Kentucky State School Board reversed its decision to use BCE and CE in the state's new Program of Studies, leaving education of students about these concepts a matter of local discretion. The use of CE in Jewish scholarship was historically motivated by the desire to avoid the implicit "Our Lord" in the abbreviation AD . Although other aspects of dating systems are based in Christian origins, AD
11544-523: The apparent motion of the planets were developed in the 4th century BC by Eudoxus of Cnidus and Callippus of Cyzicus . Their models were based on nested homocentric spheres centered upon the Earth. Their younger contemporary Heraclides Ponticus proposed that the Earth rotates around its axis. A different approach to celestial phenomena was taken by natural philosophers such as Plato and Aristotle . They were less concerned with developing mathematical predictive models than with developing an explanation of
11700-531: The application of mathematics to their prediction is Babylonian. Tablets dating back to the Old Babylonian period document the application of mathematics to the variation in the length of daylight over a solar year. Centuries of Babylonian observations of celestial phenomena are recorded in the series of cuneiform tablets known as the Enūma Anu Enlil . The oldest significant astronomical text that we possess
11856-611: The area. An important contribution by Islamic astronomers was their emphasis on observational astronomy . This led to the emergence of the first astronomical observatories in the Muslim world by the early 9th century. Zij star catalogues were produced at these observatories. In the 9th century, Persian astrologer Albumasar was thought to be one of the greatest astrologer at that time. His practical manuals for training astrologers profoundly influenced Muslim intellectual history and, through translations, that of western Europe and Byzantium In
12012-455: The axial tilt is not constant but was in fact decreasing. In 11th-century Persia, Omar Khayyám compiled many tables and performed a reformation of the calendar that was more accurate than the Julian and came close to the Gregorian . Other Muslim advances in astronomy included the collection and correction of previous astronomical data, resolving significant problems in the Ptolemaic model ,
12168-515: The beginning of the inundation was a particularly important point to fix in the yearly calendar. Writing in the Roman era , Clement of Alexandria gives some idea of the importance of astronomical observations to the sacred rites: And after the Singer advances the Astrologer (ὡροσκόπος), with a horologium (ὡρολόγιον) in his hand, and a palm (φοίνιξ), the symbols of astrology . He must know by heart
12324-476: The contents of intergalactic space . The universe also includes the physical laws that influence energy and matter, such as conservation laws , classical mechanics , and relativity . The universe is often defined as "the totality of existence", or everything that exists, everything that has existed, and everything that will exist. In fact, some philosophers and scientists support the inclusion of ideas and abstract concepts—such as mathematics and logic—in
12480-615: The continent's intellectual production. The advanced astronomical treatises of classical antiquity were written in Greek , and with the decline of knowledge of that language, only simplified summaries and practical texts were available for study. The most influential writers to pass on this ancient tradition in Latin were Macrobius , Pliny , Martianus Capella , and Calcidius . In the 6th century Bishop Gregory of Tours noted that he had learned his astronomy from reading Martianus Capella, and went on to employ this rudimentary astronomy to describe
12636-453: The definition of the universe. The word universe may also refer to concepts such as the cosmos , the world , and nature . The word universe derives from the Old French word univers , which in turn derives from the Latin word universus , meaning 'combined into one'. The Latin word 'universum' was used by Cicero and later Latin authors in many of the same senses as
12792-546: The density of matter was less than the density of dark energy, marking the beginning of the present dark-energy-dominated era . In this era, the expansion of the universe is accelerating due to dark energy. Of the four fundamental interactions , gravitation is the dominant at astronomical length scales. Gravity's effects are cumulative; by contrast, the effects of positive and negative charges tend to cancel one another, making electromagnetism relatively insignificant on astronomical length scales. The remaining two interactions,
12948-598: The development of Babylonian astronomy took place during the time of the Seleucid Empire (323–60 BC). In the 3rd century BC, astronomers began to use "goal-year texts" to predict the motions of the planets. These texts compiled records of past observations to find repeating occurrences of ominous phenomena for each planet. About the same time, or shortly afterwards, astronomers created mathematical models that allowed them to predict these phenomena directly, without consulting records. A notable Babylonian astronomer from this time
13104-496: The development of the universal latitude-independent astrolabe by Arzachel , the invention of numerous other astronomical instruments, Ja'far Muhammad ibn Mūsā ibn Shākir 's belief that the heavenly bodies and celestial spheres were subject to the same physical laws as Earth , and the introduction of empirical testing by Ibn al-Shatir , who produced the first model of lunar motion which matched physical observations. Natural philosophy (particularly Aristotelian physics )
13260-407: The earliest state of the universe was an extremely hot and dense one, and that the universe subsequently expanded and cooled. The model is based on general relativity and on simplifying assumptions such as the homogeneity and isotropy of space. A version of the model with a cosmological constant (Lambda) and cold dark matter , known as the Lambda-CDM model , is the simplest model that provides
13416-462: The early 20th century. The phrase "common era", in lower case , also appeared in the 19th century in a "generic" sense, not necessarily to refer to the Christian Era, but to any system of dates in common use throughout a civilization. Thus, "the common era of the Jews", "the common era of the Mahometans", "common era of the world", "the common era of the foundation of Rome". When it did refer to
13572-453: The education of clergy from the 7th century until well after the rise of the Universities in the 12th century . The range of surviving ancient Roman writings on astronomy and the teachings of Bede and his followers began to be studied in earnest during the revival of learning sponsored by the emperor Charlemagne . By the 9th century rudimentary techniques for calculating the position of
13728-411: The energy of each photon decreases as it is cosmologically redshifted . At around 47,000 years, the energy density of matter became larger than that of photons and neutrinos , and began to dominate the large scale behavior of the universe. This marked the end of the radiation-dominated era and the start of the matter-dominated era . In the earliest stages of the universe, tiny fluctuations within
13884-428: The entry for CE/BCE: "some people prefer CE (common era, current era, or Christian era) and BCE (before common era, etc.) to AD and BC, which, however, remain our style". In the United States, the use of the BCE/CE notation in textbooks was reported in 2005 to be growing. Some publications have transitioned to using it exclusively. For example, the 2007 World Almanac was the first edition to switch to BCE/CE, ending
14040-399: The first 10 seconds. This initial period of inflation would explain why space appears to be very flat . Within the first fraction of a second of the universe's existence, the four fundamental forces had separated. As the universe continued to cool from its inconceivably hot state, various types of subatomic particles were able to form in short periods of time known as the quark epoch ,
14196-476: The first subatomic particles and simple atoms to form. Giant clouds of hydrogen and helium were gradually drawn to the places where matter was most dense , forming the first galaxies, stars, and everything else seen today. From studying the effects of gravity on both matter and light, it has been discovered that the universe contains much more matter than is accounted for by visible objects; stars, galaxies, nebulas and interstellar gas. This unseen matter
14352-399: The first measurement of precession and the compilation of the first star catalog in which he proposed our modern system of apparent magnitudes . The Antikythera mechanism , an ancient Greek astronomical observational device for calculating the movements of the Sun and the Moon, possibly the planets, dates from about 150–100 BC, and was the first ancestor of an astronomical computer . It
14508-430: The first time. Unlike plasma, neutral atoms are transparent to many wavelengths of light, so for the first time the universe also became transparent. The photons released (" decoupled ") when these atoms formed can still be seen today; they form the cosmic microwave background (CMB). As the universe expands, the energy density of electromagnetic radiation decreases more quickly than does that of matter because
14664-450: The flooding of the Nile. It is also the origin of the phrase 'dog days of summer'. Astronomy played a considerable part in religious matters for fixing the dates of festivals and determining the hours of the night . The titles of several temple books are preserved recording the movements and phases of the Sun , Moon and stars . The rising of Sirius ( Egyptian : Sopdet, Greek : Sothis) at
14820-486: The fourth year of Jesus Christ, the first of which was but eight days", and also refers to the common era as a synonym for vulgar era with "the fact that our Lord was born on the 4th year before the vulgar era, called Anno Domini, thus making (for example) the 42d year from his birth to correspond with the 38th of the common era". The Catholic Encyclopedia (1909) in at least one article reports all three terms (Christian, Vulgar, Common Era) being commonly understood by
14976-427: The gradual reionization of the universe between about 200–500 million years and 1 billion years, and also for seeding the universe with elements heavier than helium, through stellar nucleosynthesis . The universe also contains a mysterious energy—possibly a scalar field —called dark energy , the density of which does not change over time. After about 9.8 billion years, the universe had expanded sufficiently so that
15132-519: The heavens attained in the 3rd millennium BC. It has been shown the Pyramids were aligned towards the pole star , which, because of the precession of the equinoxes , was at that time Thuban , a faint star in the constellation of Draco . Evaluation of the site of the temple of Amun-Re at Karnak , taking into account the change over time of the obliquity of the ecliptic , has shown that the Great Temple
15288-423: The mid-19th century by Jewish religious scholars. Since the late 20th century, BCE and CE have become popular in academic and scientific publications on the grounds that BCE and CE are religiously neutral terms. They have been promoted as more sensitive to non-Christians by not referring to Jesus , the central figure of Christianity , especially via the religious terms " Christ " and Dominus ("Lord") used by
15444-404: The model of concentric spheres to employ more complex models in which an eccentric circle would carry around a smaller circle, called an epicycle which in turn carried around a planet. The first such model is attributed to Apollonius of Perga and further developments in it were carried out in the 2nd century BC by Hipparchus of Nicea . Hipparchus made a number of other contributions, including
15600-544: The modern English word is used. A term for universe among the ancient Greek philosophers from Pythagoras onwards was τὸ πᾶν ( tò pân ) 'the all', defined as all matter and all space, and τὸ ὅλον ( tò hólon ) 'all things', which did not necessarily include the void. Another synonym was ὁ κόσμος ( ho kósmos ) meaning 'the world , the cosmos '. Synonyms are also found in Latin authors ( totum , mundus , natura ) and survive in modern languages, e.g.,
15756-448: The modern universe. From approximately 10 seconds after the Big Bang , during a period known as the hadron epoch , the temperature of the universe had fallen sufficiently to allow quarks to bind together into hadrons, and the mass of the universe was dominated by hadrons . Initially, the temperature was high enough to allow the formation of hadron–anti-hadron pairs, which kept matter and antimatter in thermal equilibrium . However, as
15912-546: The month to the phases of the Moon and divided the year into twelve almost-equal months, that mostly alternated between thirty and thirty-one days. Julius Caesar instigated calendar reform in 46 BC and introduced what is now called the Julian calendar , based upon the 365 + 1 ⁄ 4 day year length originally proposed by the 4th century BC Greek astronomer Callippus . Ancient astronomical artifacts have been found throughout Europe . The artifacts demonstrate that Neolithic and Bronze Age Europeans had
16068-541: The next heavier element, carbon , was not formed in significant amounts. Big Bang nucleosynthesis shut down after about 20 minutes due to the rapid drop in temperature and density of the expanding universe. Subsequent formation of heavier elements resulted from stellar nucleosynthesis and supernova nucleosynthesis . Ordinary matter and the forces that act on matter can be described in terms of elementary particles . These particles are sometimes described as being fundamental, since they have an unknown substructure, and it
16224-518: The observed rate of expansion. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant can be formulated to be equivalent to vacuum energy . Dark matter is a hypothetical kind of matter that is invisible to the entire electromagnetic spectrum , but which accounts for most of the matter in the universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, radiation, and
16380-464: The other abbreviations. Nevertheless, its epoch remains the same as that used for the Anno Domini era. The idea of numbering years beginning from the date that he believed to be the date of birth of Jesus , was conceived around the year 525 by the Christian monk Dionysius Exiguus . He did this to replace the then dominant Era of Martyrs system, because he did not wish to continue the memory of
16536-428: The other fundamental forces, and all the forces may have been unified . The physics controlling this very early period (including quantum gravity in the Planck epoch) is not understood, so we cannot say what, if anything, happened before time zero . Since the Planck epoch, the universe has been expanding to its present scale, with a very short but intense period of cosmic inflation speculated to have occurred within
16692-550: The planets were circulating in Western Europe; medieval scholars recognized their flaws, but texts describing these techniques continued to be copied, reflecting an interest in the motions of the planets and in their astrological significance. Universe The universe is all of space and time and their contents. It comprises all of existence , any fundamental interaction , physical process and physical constant , and therefore all forms of matter and energy , and
16848-455: The planets). He also calculated the time taken for the Earth to orbit the Sun to 9 decimal places. The Buddhist University of Nalanda at the time offered formal courses in astronomical studies. Other important astronomers from India include Madhava of Sangamagrama , Nilakantha Somayaji and Jyeshtadeva , who were members of the Kerala school of astronomy and mathematics from the 14th century to
17004-442: The possibilities that the universe has more dimensions (which is postulated by theories such as string theory) and that its spacetime may have a multiply connected global topology, in analogy with the cylindrical or toroidal topologies of two-dimensional spaces . General relativity describes how spacetime is curved and bent by mass and energy (gravity). The topology or geometry of the universe includes both local geometry in
17160-422: The practice of dating years before what he supposed was the year of birth of Jesus, without a year zero . In 1422, Portugal became the last Western European country to switch to the system begun by Dionysius. The term "Common Era" is traced back in English to its appearance as " Vulgar Era" to distinguish years of the Anno Domini era, which was in popular use, from dates of the regnal year (the year of
17316-458: The presence of other masses. A remark by John Archibald Wheeler that has become proverbial among physicists summarizes the theory: "Spacetime tells matter how to move; matter tells spacetime how to curve", and therefore there is no point in considering one without the other. The Newtonian theory of gravity is a good approximation to the predictions of general relativity when gravitational effects are weak and objects are moving slowly compared to
17472-408: The present dark-energy era, it dominates the mass–energy of the universe because it is uniform across space. Two proposed forms for dark energy are the cosmological constant , a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli , dynamic quantities whose energy density can vary in time and space while still permeating them enough to cause
17628-462: The reasons for the motions of the Cosmos. In his Timaeus , Plato described the universe as a spherical body divided into circles carrying the planets and governed according to harmonic intervals by a world soul . Aristotle, drawing on the mathematical model of Eudoxus, proposed that the universe was made of a complex system of concentric spheres , whose circular motions combined to carry the planets around
17784-471: The reign of Nabonassar (747–733 BC). The systematic records of ominous phenomena in Babylonian astronomical diaries that began at this time allowed for the discovery of a repeating 18-year cycle of lunar eclipses , for example. The Greek astronomer Ptolemy later used Nabonassar's reign to fix the beginning of an era, since he felt that the earliest usable observations began at this time. The last stages in
17940-455: The reign of a sovereign) typically used in national law. (The word 'vulgar' originally meant 'of the ordinary people', with no derogatory associations. ) The first use of the Latin term anno aerae nostrae vulgaris may be that in a 1615 book by Johannes Kepler . Kepler uses it again, as ab Anno vulgaris aerae , in a 1616 table of ephemerides , and again, as ab anno vulgaris aerae , in 1617. A 1635 English edition of that book has
18096-576: The rumours and stated that the BC/AD notation would remain, with CE and BCE as an optional suggested learning activity. In 2013, the Canadian Museum of Civilization (now the Canadian Museum of History) in Gatineau (opposite Ottawa ), which had previously switched to BCE/CE, decided to change back to BC/AD in material intended for the public while retaining BCE/CE in academic content. The notation
18252-456: The same from all vantage points and has no center. An explanation for why the expansion of the universe is accelerating remains elusive. It is often attributed to the gravitational influence of "dark energy", an unknown form of energy that is hypothesized to permeate space. On a mass–energy equivalence basis, the density of dark energy (~ 7 × 10 g/cm ) is much less than the density of ordinary matter or dark matter within galaxies. However, in
18408-456: The same time, a second observer who is moving relative to the first will see those events happening at different times. The two observers will disagree on the time T {\displaystyle T} between the events, and they will disagree about the distance D {\displaystyle D} separating the events, but they will agree on the speed of light c {\displaystyle c} , and they will measure
18564-477: The same value for the combination c 2 T 2 − D 2 {\displaystyle c^{2}T^{2}-D^{2}} . The square root of the absolute value of this quantity is called the interval between the two events. The interval expresses how widely separated events are, not just in space or in time, but in the combined setting of spacetime. The special theory of relativity cannot account for gravity . Its successor,
18720-401: The second derivative of the cosmic scale factor a ¨ {\displaystyle {\ddot {a}}} has been positive in the last 5–6 billion years. Modern physics regards events as being organized into spacetime . This idea originated with the special theory of relativity , which predicts that if one observer sees two events happening in different places at
18876-414: The speed of light, 13.8 billion light-years (4.2 × 10 ^ pc), the proper distance is larger because the edge of the observable universe and the Earth have since moved further apart. For comparison, the diameter of a typical galaxy is 30,000 light-years (9,198 parsecs ), and the typical distance between two neighboring galaxies is 3 million light-years (919.8 kiloparsecs). As an example,
19032-449: The speed of light. The relation between matter distribution and spacetime curvature is given by the Einstein field equations , which require tensor calculus to express. The universe appears to be a smooth spacetime continuum consisting of three spatial dimensions and one temporal ( time ) dimension. Therefore, an event in the spacetime of the physical universe can be identified by
19188-483: The standard model of cosmology, describing a flat , homogeneous universe presently dominated by dark matter and dark energy . The fine-tuned universe hypothesis is the proposition that the conditions that allow the existence of observable life in the universe can only occur when certain universal fundamental physical constants lie within a very narrow range of values. According to this hypothesis, if any of several fundamental constants were only slightly different,
19344-433: The statistical properties of the universe are the same in all directions as observed from Earth. The universe is bathed in highly isotropic microwave radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.72548 kelvins . The hypothesis that the large-scale universe is homogeneous and isotropic is known as the cosmological principle . A universe that is both homogeneous and isotropic looks
19500-421: The structures they form, from sub-atomic particles to entire galactic filaments . Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787 ± 0.020 billion years ago and that the universe has been expanding since then. The portion of the universe that we can see is approximately 93 billion light-years in diameter at present, but
19656-528: The task of recording very large and very small numbers. The modern practice of dividing a circle into 360 degrees , or an hour into 60 minutes, began with the Sumerians. For more information, see the articles on Babylonian numerals and mathematics . Classical sources frequently use the term Chaldeans for the astronomers of Mesopotamia, who were, in reality, priest-scribes specializing in astrology and other forms of divination . The first evidence of recognition that astronomical phenomena are periodic and of
19812-404: The temperature of the universe continued to fall, hadron–anti-hadron pairs were no longer produced. Most of the hadrons and anti-hadrons were then eliminated in particle–antiparticle annihilation reactions, leaving a small residual of hadrons by the time the universe was about one second old. A lepton is an elementary , half-integer spin particle that does not undergo strong interactions but
19968-461: The time is given in the tables as in the centre, on the left eye, on the right shoulder, etc. According to the texts, in founding or rebuilding temples the north axis was determined by the same apparatus, and we may conclude that it was the usual one for astronomical observations. In careful hands it might give results of a high degree of accuracy. The astronomy of East Asia began in China . Solar term
20124-488: The title page in English that may be the earliest-found use of Vulgar Era in English. A 1701 book edited by John Le Clerc includes the phrase "Before Christ according to the Vulgar Æra, 6". The Merriam Webster Dictionary gives 1716 as the date of first use of the term "vulgar era" (which it defines as Christian era). The first published use of "Christian Era" may be the Latin phrase annus aerae christianae on
20280-480: The title page of a 1584 theology book, De Eucharistica controuersia . In 1649, the Latin phrase annus æræ Christianæ appeared in the title of an English almanac. A 1652 ephemeris may be the first instance found so far of the English use of "Christian Era". The English phrase "Common Era" appears at least as early as 1708, and in a 1715 book on astronomy it is used interchangeably with "Christian Era" and "Vulgar Era". A 1759 history book uses common æra in
20436-404: The tombs of Rameses VI and Rameses IX it seems that for fixing the hours of the night a man seated on the ground faced the Astrologer in such a position that the line of observation of the pole star passed over the middle of his head. On the different days of the year each hour was determined by a fixed star culminating or nearly culminating in it, and the position of these stars at
20592-476: The total matter in the universe. The remaining 4.9% of the mass–energy of the universe is ordinary matter, that is, atoms , ions , electrons and the objects they form. This matter includes stars , which produce nearly all of the light we see from galaxies, as well as interstellar gas in the interstellar and intergalactic media, planets , and all the objects from everyday life that we can bump into, touch or squeeze. The great majority of ordinary matter in
20748-461: The total size of the universe is not known. Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric , placing Earth at the center. Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System . In developing
20904-486: The traditional Jewish designations – B.C.E. and C.E. – cast a wider net of inclusion." In the World History Encyclopedia , Joshua J. Mark wrote "Non-Christian scholars, especially, embraced [CE and BCE] because they could now communicate more easily with the Christian community. Jewish, Islamic, Hindu and Buddhist scholars could retain their [own] calendar but refer to events using
21060-488: The universe entered a period known as the photon epoch . During this period, the universe was still far too hot for matter to form neutral atoms , so it contained a hot, dense, foggy plasma of negatively charged electrons , neutral neutrinos and positive nuclei. After about 377,000 years, the universe had cooled enough that electrons and nuclei could form the first stable atoms . This is known as recombination for historical reasons; electrons and nuclei were combining for
21216-406: The universe had a beginning and has been expanding since then. According to the Big Bang theory, the energy and matter initially present have become less dense as the universe expanded. After an initial accelerated expansion called the inflationary epoch at around 10 seconds, and the separation of the four known fundamental forces , the universe gradually cooled and continued to expand, allowing
21372-454: The universe has decreased by 1/2 in the past 2 billion years. Today, ordinary matter, which includes atoms, stars, galaxies, and life , accounts for only 4.9% of the contents of the universe. The present overall density of this type of matter is very low, roughly 4.5 × 10 grams per cubic centimeter, corresponding to a density of the order of only one proton for every four cubic meters of volume. The nature of both dark energy and dark matter
21528-406: The universe has expanded monotonically . Perhaps unsurprisingly , our universe has just the right mass–energy density , equivalent to about 5 protons per cubic meter, which has allowed it to expand for the last 13.8 billion years, giving time to form the universe as observed today. There are dynamical forces acting on the particles in the universe which affect the expansion rate. Before 1998, it
21684-482: The universe is unseen, since visible stars and gas inside galaxies and clusters account for less than 10 percent of the ordinary matter contribution to the mass–energy density of the universe. Ordinary matter commonly exists in four states (or phases ): solid , liquid , gas , and plasma . However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates . Ordinary matter
21840-422: The universe would have been unlikely to be conducive to the establishment and development of matter , astronomical structures, elemental diversity, or life as it is understood. Whether this is true, and whether that question is even logically meaningful to ask, are subjects of much debate. The proposition is discussed among philosophers , scientists , theologians , and proponents of creationism . The universe
21996-467: The universe's density led to concentrations of dark matter gradually forming. Ordinary matter, attracted to these by gravity , formed large gas clouds and eventually, stars and galaxies, where the dark matter was most dense, and voids where it was least dense. After around 100–300 million years, the first stars formed, known as Population III stars. These were probably very massive, luminous, non metallic and short-lived. They were responsible for
22152-663: The wall of the Lascaux caves in France dating from 33,000 to 10,000 years ago could be a graphical representation of the Pleiades , the Summer Triangle , and the Northern Crown . Ancient structures with possibly astronomical alignments (such as Stonehenge ) probably fulfilled astronomical, religious , and social functions . Calendars of the world have often been set by observations of
22308-550: The workings of the universe. During the Renaissance Period, revolutionary ideas emerged about astronomy. One such idea was contributed in 1593 by Polish astronomer Nicolaus Copernicus , who developed a heliocentric model that depicted the planets orbiting the sun. This was the start of the Copernican Revolution . The success of astronomy, compared to other sciences, was achieved because of several reasons. Astronomy
22464-756: Was Seleucus of Seleucia , who was a supporter of the heliocentric model . Babylonian astronomy was the basis for much of what was done in Greek and Hellenistic astronomy , in classical Indian astronomy , in Sassanian Iran, in Byzantium, in Syria, in Islamic astronomy , in Central Asia, and in Western Europe. Astronomy in the Indian subcontinent dates back to the period of Indus Valley Civilisation during 3rd millennium BC, when it
22620-551: Was advanced during the Shunga Empire and many star catalogues were produced during this time. The Shunga period is known as the "Golden age of astronomy in India". It saw the development of calculations for the motions and places of various planets, their rising and setting, conjunctions , and the calculation of eclipses. Indian astronomers by the 6th century believed that comets were celestial bodies that re-appeared periodically. This
22776-427: Was aligned on the rising of the midwinter Sun. The length of the corridor down which sunlight would travel would have limited illumination at other times of the year. The Egyptians also found the position of Sirius (the dog star) who they believed was Anubis, their Jackal headed god, moving through the heavens. Its position was critical to their civilisation as when it rose heliacal in the east before sunrise it foretold
22932-517: Was completed in Warring States period . The knowledge of Chinese astronomy was introduced into East Asia. Astronomy in China has a long history. Detailed records of astronomical observations were kept from about the 6th century BC, until the introduction of Western astronomy and the telescope in the 17th century. Chinese astronomers were able to precisely predict eclipses. Much of early Chinese astronomy
23088-448: Was discovered in an ancient shipwreck off the Greek island of Antikythera , between Kythera and Crete . The device became famous for its use of a differential gear , previously believed to have been invented in the 16th century, and the miniaturization and complexity of its parts, comparable to a clock made in the 18th century. The original mechanism is displayed in the Bronze collection of
23244-485: Was expected that the expansion rate would be decreasing as time went on due to the influence of gravitational interactions in the universe; and thus there is an additional observable quantity in the universe called the deceleration parameter , which most cosmologists expected to be positive and related to the matter density of the universe. In 1998, the deceleration parameter was measured by two different groups to be negative, approximately −0.55, which technically implies that
23400-445: Was for the purpose of timekeeping. The Chinese used a lunisolar calendar, but because the cycles of the Sun and the Moon are different, astronomers often prepared new calendars and made observations for that purpose. Astrological divination was also an important part of astronomy. Astronomers took careful note of "guest stars" ( Chinese : 客星 ; pinyin : kèxīng ; lit. 'guest star') which suddenly appeared among
23556-482: Was made by Gan De , a Chinese astronomer , in the 4th century BC. Maya astronomical codices include detailed tables for calculating phases of the Moon , the recurrence of eclipses, and the appearance and disappearance of Venus as morning and evening star . The Maya based their calendrics in the carefully calculated cycles of the Pleiades , the Sun , the Moon , Venus , Jupiter , Saturn , Mars , and also they had
23712-484: Was mathematically more efficient than the Tychonic system, due to correctly taking into account the equation of the centre and latitudinal motion of Mercury and Venus. Most astronomers of the Kerala school of astronomy and mathematics who followed him accepted his planetary model. After the significant contributions of Greek scholars to the development of astronomy, it entered a relatively static era in Western Europe from
23868-464: Was separated from astronomy by Ibn al-Haytham (Alhazen) in the 11th century, by Ibn al-Shatir in the 14th century, and Qushji in the 15th century. Bhāskara II (1114–1185) was the head of the astronomical observatory at Ujjain, continuing the mathematical tradition of Brahmagupta. He wrote the Siddhantasiromani which consists of two parts: Goladhyaya (sphere) and Grahaganita (mathematics of
24024-556: Was the first science to have a mathematical foundation and have sophisticated procedures such as using armillary spheres and quadrants. This provided a solid base for collecting and verifying data. Throughout the years, astronomy has broadened into multiple subfields such as astrophysics , observational astronomy , theoretical astronomy , and astrobiology . Early cultures identified celestial objects with gods and spirits. They related these objects (and their movements) to phenomena such as rain , drought , seasons , and tides . It
24180-473: Was the view expressed in the 6th century by the astronomers Varahamihira and Bhadrabahu, and the 10th-century astronomer Bhattotpala listed the names and estimated periods of certain comets, but it is unfortunately not known how these figures were calculated or how accurate they were. The Ancient Greeks developed astronomy, which they treated as a branch of mathematics, to a highly sophisticated level. The first geometrical, three-dimensional models to explain
24336-566: Was used to create calendars. As the Indus Valley civilization did not leave behind written documents, the oldest extant Indian astronomical text is the Vedanga Jyotisha , dating from the Vedic period . The Vedanga Jyotisha is attributed to Lagadha and has an internal date of approximately 1350 BC, and describes rules for tracking the motions of the Sun and the Moon for the purposes of ritual. It
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