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'']] , a discipline long interwoven with astronomy, and not completely separate from it until about 1750‑1800 in the Western World . Early astronomy involved observing and predicting the motions of Visible Celestial objects, especially Star s and Naked Eye Planets . An example of this early astronomy might involve a study of the Relationships between the " Apparent Height " or Altitude of the Noon Sun , and the changing Pattern s of Night time Star s. Eventually Astrological Charts were drawn up by cultures around the world using the raw astronomical data collected. Ancient astronomers were able to differentiate between stars and Planets , as stars remain relatively fixed over the Centuries while planets will move an appreciable amount during a comparatively short time. ANCIENT HISTORY Early Culture s identifed celestial objects with God s and Spirit s. They related these objects (and their movements) to phenomena such as Rain , Drought , Season s, and Tide s. It is generally believed that the first "professional" astronomers were Priest s (such as the Magi ), and that their understanding of the " Heaven s" was seen as " Divine ", hence astronomy's ancient connection to what is now called astrology. Ancient constructions with astronomical Alineation s (such as Stonehenge ) probably fulfilled both astronomical and Religious Function s. Calendar s of the world have usually been set by the Sun and Moon (measuring the Day , Month and Year ), and were of importance to Agricultural societies, in which the harvest depended on planting at the correct time of year. The most common Modern Calendar is based on the Roman calendar, which divided the year into twelve months of alternating thirty and thirty-one days apiece. In 46 BC Julius Caesar instigated Calendar Reform and created the Leap Year . INDIA ''See also:'' Hindu Astronomy There are astronomical references of chronological significance in the Vedas . Some Vedic notices mark the beginning of the year and that of the Vernal Equinox in Orion ; this was the case around 4500 BC. Fire altars, with astronomical basis, have been found in the third millennium cities of India. The texts that describe their designs are conservatively dated to the first millennium BC, but their contents appear to be much older. Yajnavalkya (perhaps 1800 BC ) described the motions of the Sun and the Moon in his book Shatapatha Brahmana , and also advanced a 95-year cycle to synchronize the motions of the Sun and the Moon. The ''Vedanga Jyotisha'', a text on Vedic Astrology that has been dated to 1350 BC , was written by Lagadha . It describes rules for tracking the motions of the Sun and the Moon, and also develops the use of Geometry and Trigonometry for astronomical uses. Around 500 CE, Aryabhata presented a mathematical system that took the Earth to spin on its axis and considered the motions of the planets with respect to the Sun. He also made an accurate approximation of the Earth's Circumference and Diameter , and also discovered how the Lunar Eclipse and Solar Eclipse happen. He gives the Radius of the planetary Orbit s in terms of the radius of the Earth/Sun orbit as essentially their periods of rotation around the Sun. He was also the earliest to discover that the orbits of the planets around the Sun are Ellipse s. {Link without Title} Brahmagupta (598-668) was the head of the astronomical Observatory at Ujjain and during his tenure there wrote a text on astronomy, the '' Brahmasphutasiddhanta '' in 628 . He was the earliest to use Algebra to solve astronomical problems. He also developed methods for calculations of the motions and places of various planets, their rising and setting, Conjunctions , and the calculation of eclipses. Bhaskara (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 the planets). He also calculated the time taken for the Earth to orbit the sun to 9 decimal places. Other important astronomers from India include Madhava , Nilakantha Somayaji and Jyeshtadeva , who were members of the Kerala School of astronomy and mathematics from the 14th Century to the 16th Century . They were responsible for founding Calculus and modern Mathematical Analysis , along with a number of other developments. MESOAMERICA Maya civilization The Maya calculated the Solar Year to somewhat greater accuracy than the Gregorian Calendar . They made detailed tables for calculating Phases Of The Moon and the movements of Venus for centuries in the past or future. Astronomy and the measurement of time were vitally important components of Maya Religion . The Maya also carefully tracked the phases of the Moon and the motions of the naked eye planets. To the ancient Maya, Venus was the patron of war and many recorded battles are timed to the motions of this planet. Mars is also mentioned in preserved astronomical Codices and early Mythology . EAST ASIA China ''See also:'' Chinese Astronomy , Chinese Astrology , Timeline Of Chinese Astronomy Ancient Chinese astronomy dates back more than two millennia. Astronomy was an important part of Science And Technology In China . Chinese astronomers were to be able to predict Comets and eclipses precisely. Any inaccuracy and the Emperor would order the astronomer to be beheaded. They were also among the first to record observations of a Supernova . Korea , world's first Astronomical Observatory .]] East Asia's first astronomical observatory was developed in kingdom of Silla , one of Three Kingdoms Of Korea . It literally means ''Star-gazing Tower'' in Korean . It was constructed under Queen Seondeok Of Silla 's reign during the 7th century. It still survives to this day. {Link without Title} MESOPOTAMIA The origins of Western 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 BCE. The Sumerians only practiced a basic form of astronomy, but they had an important influence on the sophisticated astronomy of the Babylonians. 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 the task of recording very large and very small numbers. The modern practice of dividing a circle into 360 degrees, of 60 minutes each, 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 earliest activities of Babylonian astronomers were limited to the recording of significant astronomical phenomena that they regarded as Omens . The best known example is the Venus Tablet Of Ammisaduqa , a record of the first and last visibilities of the planet Venus observed around the 16th century BCE. The text of the Venus tablet was later included in a large compendium of omens called ''Enuma Anu Enlil''. A significant increase in the quality and frequency of Babylonian observations appeared during the reign of Nabonassar (747-733). The systematic records of lunar eclipses that began at this time allowed for the discovery of a repeating 18-year cycle, 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 the development of Babylonian astronomy took place during the time of the Seleucid Empire (323-60 BCE). In the third century, astronomers began to use "goal-year texts" to predict the motions of the planets. This method required the astronomer to consult records of past observations to find repeating patterns in the motion of each planet. About the same time, or shortly afterwards, astronomers created matheamtical models that allowed them to predict the motions of the planets directly, without consulting stacks of records. The Mesopotamian underpinnings of western astronomy are extensive. It was from the Mesopotamians that the Greeks gained their knowledge of the five visible planets and the constellations of the Zodiac , centuries of recorded astronomical observations, and even the idea that the motions of the planets could be predicted with accuracy. ANCIENT GREECE ''Main article:'' Greek Astronomy Greek Philosopher s and Mathematicians thought of several models to explain the movements of stars, planets, the Sun and the Moon. Eratosthenes , using the angles of shadows created at widely-separated regions, estimated the circumference of the Earth with great accuracy. Hipparchus made a number of important contributions, including the first measurement of Precession and the compilation of the first star catalog. Ptolemy later referred to this work in his important '' Almagest ,'' which had a lasting effect on astronomy up to the Renaissance . MIDDLE AGES & ISLAMIC ASTRONOMY ''See also:'' Islamic Astronomy Greeks made some important contributions to astronomy, but the progress was mostly stagnant in Medieval Europe . It flourished in the Arab world and priests in distant parishes needed elementary astronomical knowledge for calculating the exact date of Easter , a procedure called '' Computus ''. The Arabic world under Islam had become highly cultured, and many important works of knowledge from Ancient Greece were translated into Arabic, used and stored in libraries throughout the area. The late 9th Century Persian astronomer Al-Farghani wrote extensively on the motion of celestial bodies. His work was translated into Latin in the 12th Century . In the late 10th Century , a huge observatory was built near Tehran , Iran , by the astronomer al-Khujandi who observed a series of Meridian Transits of the Sun, which allowed him to calculate the Obliquity Of The Ecliptic , also known as the tilt of the Earth's axis relative to the Sun. In 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 . An amazing feat was his calculation of the year to be 365.24219858156 days long, which is accurate to the 6th decimal place. Meanwhile in Europe, astronomy was one of the seven Liberal Arts , making it a core subject of any Studium Generale (now known as " Universities "). The model from the Greeks most remembered through the Middle Ages was the Geocentric Model , in which the Spherical Earth was in the center of the Cosmos or Universe , with the Sun, Moon and planets each occupying its own concentric sphere. The fixed stars shared the outermost sphere. In the 14th Century , Nicole Oresme showed that the reasons proposed by the physics of Aristotle against the movement of the Earth were not valid and adduced the argument of simplicity for the theory that the earth moves, and ''not'' the heavens. However, he concluded from Biblical Passages that the Earth does not move. And in the 15th Century , Nicholas Of Cusa suggested in some of his scientific writings that the Earth revolved around the Sun, and that each star is itself a distant sun. He was not, however, describing a scientifically verifiable theory of the universe. THE COPERNICAN REVOLUTION The Renaissance came to astronomy with the work of Nicolaus Copernicus , who proposed a Heliocentric system. His work was defended, expanded upon and corrected by the likes of Galileo Galilei and Johannes Kepler . Kepler, using precise naked-eye observations made by Tycho Brahe , discovered the three Laws Of Planetary Movement that carry his name (though he published them mixed with some other ideas, and didn't give them the importance that we do). Galileo was among the first to use a Telescope to observe the sky, and after constructing a 20x Refractor Telescope he discovered the four largest Moon s of Jupiter in 1610 . This was the first observation of satellites orbiting another planet. He also found that our Moon had Craters and observed (and correctly explained) Sunspots This, along with Galileo noting that Venus exhibited a full set of Phases resembling Lunar Phase s, was seen as incompatible with the church's favoured model of the Earth at the center of the universe and led to much Controversy . UNITING PHYSICS AND ASTRONOMY Isaac Newton was the first Natural Philosopher to link physics and astronomy, via his Universal Law Of Gravity . Realising that the same force that attracted objects to the surface of the Earth held the moon in orbit around the Earth, Newton was able to explain - in one theoretical framework - all known gravitational phenomena. In his Philosophiae Naturalis Principia Mathematica , he derives Kepler's Laws Of Motion from First Principles . Newton's focus on Experimentalism lay many of the foundations of Modern Physics . MODERN ASTRONOMY At the end of the 19th century it was discovered that, when decomposing the light from the Sun, a multitude of Spectral Line s were observed (regions where there was less or no light). Experiments with hot gases showed that the same lines could be observed in the spectra of gases, specific lines corresponding to unique elements. It was proved that the Chemical Element s found in the Sun (chiefly Hydrogen and Helium ) were also found on Earth. During the 20th century Spectrometry (the study of these lines) advanced, especially because of the advent of Quantum Physics , that was necessary to understand the observations. Although in previous centuries noted astronomers were exclusively male, at the turn of the 20th century women began to play a role in the great discoveries. In this period prior to modern computers, women at the discovered the Cepheid Variable star period-luminosity relation, Annie Jump Cannon organized the stellar Spectral Types according to stellar temperature, and Maria Mitchell was the first person to discover a comet using a telescope. (See {Link without Title} for more women astronomers.) Some of these women received little or no recognition during their lives due to their lower professional standing in the field of astronomy. And although their discoveries are taught in classrooms around the world, few students of astronomy can attribute the works to their authors. COSMOLOGY AND THE EXPANSION OF THE UNIVERSE Most of our current knowledge was gained during the 20th century. With the help of the use of Photography , fainter objects were observed. Our sun was found to be part of a Galaxy made by more than 1010 stars (10 billion stars). The existence of other galaxies, one of the matters of '' The Great Debate '', was settled by Edwin Hubble , who identified the Andromeda Nebula as a different galaxy, and many others at large distances and receding, moving away from our galaxy. Cosmology , a discipline that has a large intersection with astronomy, made huge advances during the 20th century, with the model of the hot Big Bang heavily supported by the evidence provided by astronomy and physics, such as the Redshifts of very distant galaxies and radio sources, the Cosmic Microwave Background Radiation , Hubble's Law and Cosmological Abundances Of Elements . NEW WINDOWS INTO THE COSMOS OPEN Late in the 19th century, scientists began discovering forms of light which were invisible to the naked eye: X-Ray s, Gamma Ray s, Radio Wave s, Microwave s, Ultraviolet Radiation , and Infrared Radiation . This had a major impact on astronomy, spawning the fields of Infrared Astronomy , Radio Astronomy , X-ray Astronomy and finally Gamma-ray Astronomy . With the advent of Spectroscopy it was proved that other stars were similar to our own sun, but with a range of Temperature s, Mass es and sizes. The existence of our Galaxy , the Milky Way , as a separate group of stars was only proven in the 20th century, along with the existence of "external" galaxies, and soon after, the expansion of the Universe seen in the recession of most galaxies from us. The 20th century was an exciting time for astronomy, with each advance in instrumentation leading to a new breakthrough in the understanding of the universe. SEE ALSO REFERENCES
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