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| − | [[File:Old celestial-map.jpg|right|250px|thumb|''Planisphærium cœleste'' (1670); watercolor by Dutch cartographer Frederik de Wit (1630 – 1706)]]
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| − | '''Astronomy''' is "the study of objects and matter outside the earth's atmosphere and of their physical and chemical properties." <ref>http://www.m-w.com/cgi-bin/dictionary?va=astronomy</ref> It has been studied since ancient times, forming a major part of the [[religion]]s of many early [[civilization]]s such as the [[Egypt]]ians and the [[Aztecs]]. [[Stonehenge]] in [[England]] is also thought to be an astronomical observatory. The handing down of complex astronomical teachings shows these early [[civilization]]s must have had formalized systems of [[education]].
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| − | Astronomy was crucial to the development of [[safe]] and accurate [[navigation]] for ships, and observations of the movement of [[sky|heavenly bodies]] helped lead to the theories we now call [[physics]]. In fact, much of astronomy today relies on physics, thus many astronomers are considered astrophysicists.<br />
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| − | Current hot topics in astrophysics research are [[exoplanets]], [[black holes]], and the accelerating universe.
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| − | ==History==
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| − | Prior to written history, man gazed upon the stars and used them for practical reasons, such as directional indicators for nomads and seafarers, or seasonal indicators for farming. Astronomy began its start as a science in ancient Mesopotamia, when priests marked the path of the sun and familiar constellations; the ritualistic nature of these early attempts linked actual astronomical observations with the superstitions of [[astrology]], a practice that continues to this day.
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| − | The first men who studied astronomy as science were the Greeks, who linked it in their studies with a valuable mathematical tool: [[geometry]], and scientists in Greek colonies along the western coast of what is now [[Turkey]] used this tool to make more and more accurate calculations. About 400 B.C. [[Pythagoras]] came to the conclusion that the earth was spherical, and that it moved in space. Aristarchus of Samos (310-230 B.C.) discovered that the earth revolved around the sun and spun on its own axis; he would be charged with heresy against the gods as a result.
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| − | About 150 B.C. Hipparchus, despite having made very careful observations and calculations, kept to the theory that the earth was the center of the universe, with the sun, moon, planets, and stars revolving around it; ten years later Claudius Ptolemy of Alexandria would write the ''Almagest'', a work that perfected on Hipparchus' accurate calculations of the motions of the stars. His efforts would become known as the "Ptolomaic system", and would stand the tests of observation for the next 1,300 years.
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| − | The problem was time and numbers. Time was a problem because for the ancient Greeks there was no way to accurately measure it; i.e. they could not get a precise fix on the position of [[Jupiter]] at midnight if they did not tell that it was midnight. As to numbers, the largest written number was the ''myriad'', a number equivalent to 10,000. [[Archimedes]] of Syracuse (287-212 B.C.), perhaps the greatest mathematician of all time, was at home with large numbers. In his ''The Sand Reckoner'' he thought of the universe as being unable to hold as much as what he calculated to be a myriad of myriads multiplied by itself seven times, then multiplied by 1,000, which came out to be 10<sup>63</sup>
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| − | During the Middle Ages clocks were developed; the first mechanical clocks which could be wound via weights emerged about 1300 A.D. in Europe; they would not improve upon astronomy until about 1500 when [[Copernicus]] put much strain on the Ptolomaic system; his calculations proved that the sun, and not the earth, was the center of the solar system, leading to condemnation from [[Martin Luther]] and the Church for what they called his anti-Biblical heresy. Indeed, some of his fellow scientists who rushed to his defense would be burned at the stake. One scientist who condemned him - the Dane [[Tycho Brahe]] - would have no part of Copernicus, but ironically his own observations and precise calculations, as well as his designs of the best astronomical instruments of his time, would later ensure that it was Copernicus, and not Brahe, who had been correct all along.
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| − | The first man to have turned a working telescope skyward was the Italian [[Galileo]], who observed the phases of [[Venus]], the craters of the [[moon]], and most importantly, the motions of the four moons around Jupiter. Both his discoveries of the Venusian phases and Jupiter's moons could not be explained by the Ptolomaic theory; they could only be explained by the works of Copernicus, and he made his views known to the public, leading eventually to condemnation by the Church, a forced recantation, and house arrest for the remainder of his life. A generation later, [[Johannes Kepler]] (1571-1630) would take advantage of Tycho's works, leading to three astronomical laws which are still in use today:
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| − | *Orbiting bodies always travel in an elliptical course around their host;
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| − | *Planets around the sun move faster in their orbits when they are close to the sun, and slower when they are further away;
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| − | *There is a definite mathematical relationship between all the planets' distances from the sun and the times in which they orbit.
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| − | [[Issac Newton]] (1642-1727) would use both Kepler's laws and Galileo's work on mechanics in his formulations on [[gravity]]; his works and equations would lead directly to the discovery of the planets [[Neptune]] and [[Pluto]].
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| − | == Young Earth Creationism View ==
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| − | [[Young earth creationism|Young earth creationists]] believe the [[earth]] and universe are approximately 6,000 years old. Young earth creationist scientists state the following are true: there are multiple lines of evidence pointing to a young earth and universe; the old earth and universe [[paradigm]] has numerous [[anomaly|anomalies]] and uses invalid dating methods, and there are multiple citations in the secular science literature that corroborate the implausibility of the old earth and universe paradigm (for details see: [[Young earth creationism]]).
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| − | ==Starlight As An Objection To The Big Bang Theory==
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| − | The [[starlight problem]] is an argument against the [[Big Bang theory]] which theorizes that the universe is billions of years old. <ref name="aig">http://www.answersingenesis.org/creation/v25/i4/lighttravel.asp</ref> The [[creation science]] organization [[Answers in Genesis]] has stated the following regarding the starlight problem for the Big Bang Theory and the work of [[Charles W. Misner]] is cited who published his work in ''[[Physical Review Letters]]'':
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| − | {{cquote|The problem is this: even assuming the big bang timescale, there has not been enough time for light to travel between widely separated regions of space. So, how can the different regions of the current [cosmic microwave background] CMB have such precisely uniform temperatures if they have never communicated with each other? This is a light-travel–time problem.<ref name="aig" />}}
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| − | == Starlight As An Objection to Young Earth Creationism ==
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| − | Those who propose an old universe assert there is a [[starlight problem]] for the [[young earth creationism|young universe]] model. A key assumption for this objection to a young universe model is that the speed of light has been constant.
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| − | ==Major Fields in Astronomy==
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| − | *Cosmology-The study of the Universe as a whole
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| − | *Astrophysics-The physics behind astronomical objects
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| − | *Archeoastronomy-The study of how the stars influenced ancient cultures
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| − | *Radio Astronomy-Using radio waves to study the universe
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| − | *Optical Astronomy-Study of astronomical objects in the visible light range
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| − | *Planetary Science-Study of planets and moons, both in our solar system and outside our solar system
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| − | *Exobiology-Theoretical study of extraterrestrial life
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| − | *Astronautical Engineering-The design and construction of space craft
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| − | ==References==
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| − | <references/>
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| − | ==External Links==
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| − | *[http://www.nasa.gov The NASA Homepage]
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| − | *[http://photojournal.jpl.nasa.gov The NASA Planetary Photojournal]
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| − | *[http://www.aas.org American Astronomical Society]
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| − | *[http://www.britastro.org/baa/ British Astronomical Association]
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| − | *[http://www.badastronomy.com Bad Astronomy] a website that deals with myths and misconceptions in astronomy.
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| − | *[http://www.astronomychitchat.co.uk/cgi-bin/yabb2/YaBB.pl?num=1328194507 A guide on how to start]
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| − | *[http://antwrp.gsfc.nasa.gov/apod/ap080527.html Astronomy Picture of the Day] Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
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| − | [[Category:Science]]
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