ASTB03 – Assignment 6 – The Hubble Space Telescope

The Hubble Space Telescope provides a gateway for human-kind to discover and explore the depths of the universe in greater detail than ever before. It was launched into orbit on the space shuttle “Discovery”, on April 24, 1990.[1] While the telescope has only been in  orbit for 25 years, the first idea of a space telescope happened almost 100 years ago, when German scientist Hermann Oberth, who suggested sending a telescope into space on a rocket in 1923.[2] Just after World War II, in 1946, Lyman Spitzer who was a physicist and researcher at Yale, wrote a paper titled, “Astronomical Advantages of an Extra-Terrestrial Observatory”, where he argued the advantages of a space telescope over the ground-based observatories that were in operation at the time.[1][2] In his paper, he wrote that the Earth’s atmosphere blurs and distorts the light that comes from other stars and that even the most precise telescopes on Earth could not avoid this, but a telescope in space would not have to deal with this, and it would also be able to detect x-ray’s emitted from stars and other objects that would usually be blocked by the Earth’s atmosphere.[1] Spitzer headed a National Academy of Science Ad Hoc Committee on the Large Space Telescope, and in 1966, they began performing studies on the use of a space-based telescope.[1] In 1969, they published the paper, “Scientific Uses of the Large Space Telescope”,[1] and because of this, the National Academy of Science approved the telescope and soon after, NASA would as well.[1][2] In 1974, it was suggested that the telescope be equipped with interchangeable instruments that could study wavelengths that ranged from ultraviolet to visible and infrared light.[2] They also suggested a space shuttle could be used to get the telescope into orbit and could be used to repair the telescope in space or return it to Earth for repairs.[2]

The telescope now needed federal funding, which would be difficult to get, because the costs were estimated to be in the $400-$500 million range.[1] The funding was originally denied in 1975.[1] However, in the same year, the European Space Agency began working with NASA on the project.[1][2] A change needed to be made in the proposal to bring the cost down and acquire funding. This change came in the mirror, which was reduced from 3m to 2.4 m, which in turn helped lower the cost to about $200 million.[1] In 1977, Congress would approve funding for the telescope.[1][2] The design of the telescope started soon after, while Perkin-Elmer Corporation were chosen to build the mirror and optical assembly, and Lockheed Missiles and Space Company were chosen to build the spacecraft and its support systems.[1] The Europeans built the solar array that would power the telescope while in orbit.[1] NASA has originally planned to launch the telescope in 1983, which is the same year it was named after Edwin Hubble[1], but there were many delays which led to the optical assembly not being put together until 1984, and the space shuttle not being completely assembled until 1985.[1] After being completed in Dec 1985, there was a planned launch for October 1986, until, early that year when the space shuttle “Challenger” exploded just after launch, causing shuttles to be grounded until 1988.[1] Finally, in April 1990, Hubble was launched and it included the Wide Field/Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), Faint Object Camera (FOC), Faint Object Spectrograph (FOS), and High Speed Photometer (HSP).[1]

Soon after the Hubble telescope began operation, scientists noticed that the images were slightly blurred.[1] After investigating the problem, it was shown that the mirror had something called “spherical aberration”, which was caused by the edges of the mirror being ground just a little bit too flat.[1][2] This made the light that bounced off the edges focus in a slightly different spot that the light that bounced off the center, and although it was only approximately 1/50th of the thickness of a sheet of paper, it was enough to cause the images to become blurry.[1][2] Scientists came up with a solution called the Corrective Optics Space Telescope Axial Replacement (COSTAR).[1][2] This was basically a set of small mirrors that could intercept the light and correct for an errors.[2] COSTAR would be installed on the service mission in December 1993 along with the Wide Field/Planetary Camera which was replaced with the Wide Field/Planetary Camera 2.[1][2] Soon after, the telescope became fully functional and was able to return much clearer images.[1]

The Hubble Space Telescope is nearing the end of its life, where it is expected to retire sometime within the current decade.[1][2] However, the James Webb Space Telescope (JWST), is currently being worked on, and will be launched into orbit sometime within the current decade.[2] It will orbit at about 1.5 million km from the Earth and will be capable of studying objects from the earliest times of the universe.[2]

The Hubble Telescope takes about 97 minutes to complete one orbit around the Earth, which means that it is travelling around 8km/sec.[2] It is the type of telescope called a Cassegrain reflector, where light bounces of a main mirror, then bounces off a secondary mirror which focuses the light through a hole in the center of the main mirror, allowing it to reach the instruments on the telescope.[2] It weighs about 24500lbs, and when it changes angles, it spins in the opposite direction since it does not have thrusters.[3] It can generate up to 10 Terabytes of data a year.[3]

The Hubble Space Telescope was instrumental in determining a more accurate age of the universe. It was able to find white dwarf stars that could be aged at approximately 12-13 billion years old.[4] These stars are difficult to find because of how faint they are.[4] Earlier observations made be the Hubble Telescope showed that stars may have begun forming about 1 billion years after the big bang, and this data allows scientists and astronomers to make a much more accurate estimate for the age of the universe.[4] I feel this is a pretty significant moment because it allows us to make more accurate predictions of the formation of galaxies and stars, as well as seeing how the universe has changed and how long it has taken to make those changes.

Another significant moment was the detection of a supernova, 10 billion light-years away.[5] This supports the idea of dark energy, or dark matter causing the universe to accelerate in its expansion.[5] The light from the supernova appears bright, meaning that the universe was slower at the time of that supernova, but more recent supernovas appear dimmer, meaning that the universe had begun accelerating.[5] This is significant because it supports the idea of dark matter and helps explain why the universe does not collapse under the force of gravity.[5] I chose this moment because the evidence of dark matter helps answer many questions we have about how the universe interacts with itself.

A third significant moment occurred in 2008 when the Hubble Telescope took pictures of the extrasolar planet Fomalhaut b.[6] This is important because it was the first time a picture of an extrasolar planet was taken by the telescope in the visible light.[6] Usually this is done by detecting the planet’s atmosphere moving in front of its star.[6] The discoveries of these extrasolar planets then led to discovering an organic molecule in the atmosphere of these planets named, HD 189733b.[7] Unlike Fomalhaut b, this planet was found because it passed in front of its parent star.[7] I feel these discoveries are important because they help reveal different characteristics that these extrasolar planets need in order to sustain life as we know it today, and if life on other planets in the universe is possible.

The Hubble Space telescope has played a major part in what we know in modern astronomy today and has revealed many secrets of the universe that would have been impossible to learn without it. For this reason, the development of the Hubble Space Telescope can be considered one of the greatest moments in astronomy and in the history of the human race.

Links Used:

[1] http://history.nasa.gov/hubble/

[2] http://hubblesite.org/the_telescope/hubble_essentials/

[3] http://www.nasa.gov/mission_pages/hubble/story/

[4] http://hubblesite.org/newscenter/archive/releases/2002/10/

[5] http://science.nasa.gov/science-news/science-at-nasa/2001/ast03apr_1/

[6] http://www.space.com/15892-hubble-space-telescope.html

[7] http://www.nasa.gov/mission_pages/hubble/science/hst_img_20080319.html

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ASTB03 – Assignment 5 – Discoverer of Expanding Universe

Alexander Friedmann was born in St. Petersburg, Russia on June 16, 1888.[1] In his school life, he was one of the top students in his classes and had organized student protests against the repressive government in Russia at the time.[2] In 1913, he was appointed a position at the Aerological Observatory in Pavlovsk, where he studied meteorology.[1][3] In 1914, he completed his master’s degree in pure and applied mathematics, but had also done research on aeronautics, the magnetic field of the earth, the mechanics of liquids and theoretical meteorology.[1] The next year, Friedmann served in the Russian air force and was awarded a military cross for his work on several missions.[1][2] He would then later become the head of the Central Aeronautical Station in Kiev.[1]

At the conclusion of the First World War, Friedmann had become a professor at Perm University.[1][2] While the First World War had ended, there was still a Civil War happening in Russia, until 1920. This made it difficult for Friedmann and other Russian scientists to communicate with scientists around the world. When the Civil War ended in Russia, Friedmann was able to learn of Einstein’s Theory of General Relativity, which had already been published in Europe during the First World War, but was not known to Russia until the end of the Russian Civil War.[2][3]

The relationship between mass, space, and time was explained in a set of differential equations known as Einstein’s field equations.[3] Friedmann had begun to focus on attempting to solve these equations after learning of the Theory of General Relativity.[2] Scientists at the time believed the universe was static and that it has always been, and will always be the same size.[2] Friedmann however, looked at the universe as a fluid, made up of the same material, and spread in every direction.[3] He was then able to use Einstein’s field equations to show how the universe would act with the Theory of General Relativity.[3] Finally, in 1922, Friedmann was able to publish solutions to Einstein’s field equations.[1][2] There were three models created by Friedmann’s solution, one for each of the positive, negative, and zero curvature.[1] In the models, if the curvature was zero, then the universe would be flat, while a positive curvature would result in a sphere, and a negative curvature would be a hyperbolic space.[3] Once time was added to the equations, Friedmann saw that the curvature could be an increasing or periodic function, which gave way to the possibility of an expanding, dynamic universe, instead of the static universe that scientists believed.[2][3] Einstein originally believed that the solution had contained errors and called it “suspicious”.[1][2] Friedmann then wrote to Einstein with more detail of his work to try to convince him that the solution was in fact correct, but Einstein did not receive the letter right away because he was on a trip to Japan.[3] However, when he did receive the letter, he admitted that Friedmann was in fact correct and said, “. . . my criticism . . . was based on an error in my calculations. I consider that Mr. Friedmann’s results are correct and shed new light”.[2] The reason this was so important was because it created the basis that lead to the Big Bang Theory and Steady State Theory of the universe.[1][3]

Afterwards, Friedmann was given the job of the Director of the Main Geophysical Observatory in Leningrad.[1] While there, he taught George Gamow, who would go on to become a theoretical physicist and cosmologist.[1] Gamow is known for doing calculations that showed that complex nuclei (ie. helium) could be formed with the hydrogen from the Big Bang.[4] This, along with the creation of heavier elements within stars made it easy to accept the Big Bang Theory on the origins of the universe.[4]

Late in the 1920’s, both George Lemaître, and Edwin Hubble would find evidence of the expansion of the universe, which further supported Friedmann’s solutions.[2] Einstein would eventually remove the cosmological constant from his equations after evidence of redshifts by galaxies.[2] Arthur Eddington would also later go on to show that the static universe would be unstable, which provided further support of the expanding universe theory.[2]

Friedmann, after publishing his solution to Einstein’s field equations, would later take part in a balloon flight which reached an elevation of 7400m.[1] However, a few months later, on September 16, 1925, he would die of typhoid fever, which he may have caught while on vacation in Crimea.[1]

While Friedmann was a very important figure in modern astronomy, was not very well known in the western world, even with the significant contributions he made in his short life. One reason for this is that there was a disconnect between Russia and the western world during World War I, and also the following Russian Civil War.[1] Because of this, it was difficult to stay in contact with scientists outside of Russia. This meant learning about Einstein’s theories later than the rest of the world, and later having his work be less known around the world. Another possible contributing factor was that he died at a younger age, and may have been able to contribute more had he lived a longer life, thus gaining more publicity. Even though he is not as well-known as other scientists at the time, Friedmann provided the foundation for what we now know today about the origins of the universe.

 

[1] http://www.physicsoftheuniverse.com/scientists_friedmann.html

[2] http://www.decodedscience.com/alexander-friedmann-unsung-hero-of-modern-cosmology/19423

[3] http://www.brighthub.com/science/space/articles/79590.aspx

[4] http://fromdeathtolife.org/cphil/bigbang.html

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ASTB03 – Assignment 4 – The Changing Pluto

 

Pluto was, at one time, the ninth and “furthest” planet away from the sun, orbiting in what is known as the Kuiper Belt. Because of how far away Pluto is, we do not have as much information about it as we do with most of the other planets in the solar system. Pluto was named by Venetia Burney, an 11-year-old from England, who suggested the name based on the Roman god of the underworld.[1] We believe that it has an estimated diameter less than one-fifth that of Earth or only about two-thirds as wide as Earth’s moon.[1] It most likely has a rocky core, with a mantle of water ice, while containing methane and nitrogen frost on its surface.[1] The Hubble Space Telescope showed that Pluto’s crust could contain complex organic molecules, which are the building blocks of life.[1] It has also returned images showing that Pluto is reddish, yellowish and greyish in different areas.[1] Pluto has a very eccentric orbit, and at times can be closer to the sun than Neptune. When this happens, some of the surface ice on Pluto can thaw out and create an atmosphere, but then freezes and disappears as Pluto moves further away from the sun, because of temperatures reaching -225 degrees Celsius.[1] It has an orbital period of 248 earth years, but is closer to the sun than Neptune is for 20 of those years.[1] Pluto has 5 known moons, it’s largest moon being Charon. Charon is almost half the size of Pluto and experiences the same tidal locking as Earth and its moon.[1] Pluto’s other 4 moons, Nix, Hydra, Kerberos, and Styx are all very small ranging in sizes between 13-100 km wide.[1] Another interesting property about Pluto is that its orbit is tilted 17 degrees relative to the rest of the solar system, unlike the rest of the planets that stay close to the plane of the solar system.[2]

Pluto was discovered by Clyde Tombaugh, on February 18, 1930.[3] Tombaugh used a telescope that had a camera that took pictures of the sky on different days. He then used a blink compactor (comparator) which flips between the pictures, allowing him to compare the two pictures and look for any objects that showed any motion between the pictures.[3] This is how Pluto was discovered.

Clyde Tombaugh was born on February 4, 1906, in Illinois.[3] He constructed his own telescopes throughout his life, completing his first one at the age of 20.[3] He used these to make more detailed observations of Mars and Jupiter, and sent these observations to Lowell Observatory, where he would be offered a job to operate their new telescope.[3] This is where he would later discover Pluto. In World War II, he taught navigation to the U.S Navy at Arizona State College, and later worked at the ballistics research lab at White Sands Missile Range in New Mexico.[3] He would also catalog over 30 000 celestial objects throughout his life.[4] He died on Jan 17, 1999, in New Mexico.[3]

The American astronomer Percival Lowell, is where the search for another planet beyond Neptune began. He studied the orbits of Uranus and Neptune, and noticed irregularities which he determined were caused by a planet beyond Neptune.[1][5] He predicted a probable location of the planet and organized a search for the planet in 1915.[1][5] This eventually lead to Tombaugh getting a job at the Observatory, as mentioned earlier, and becoming part of the search 13 years later. While there was an organized search for Pluto and there was a prediction on its possible location, it is a little difficult to say that it was found based on theoretical predictions. Unlike Neptune, which was found very quickly after calculating its predicted location, Pluto was not found until 1930. 15 years after Lowell had made a prediction about its location.[5] On the other hand, it was calculations of the orbits of Uranus and Neptune that lead to the search for Pluto in the first place, so Pluto’s discovery was not entirely luck based either.

Pluto has sparked interesting debates since its discovery in 1930. When Charon was discovered in 1978, it was determined that Pluto was not actually as large as first thought because of how close Charon is to Pluto and the size of Charon, in relation to Pluto.[6] As mentioned earlier, Pluto has an atmosphere as it gets closer to the Sun, but loses that atmosphere as it moves further away. Pluto’s biggest debate is its reclassification as a dwarf planet.[6] With objects such as Ceres, Eris (discovered in 2003), and other Trans-Neptunian objects found, The (IAU) International Astronomical Union, had to redefine what a “planet” was.[7] After gathering information and opinion from multiple sources such as “professional astronomers, planetary scientists, historians, science publishers, writers and educators”[7], the IAU redefined what a planet is, and Pluto did not match the criteria. In 2006, Pluto was reclassified as a dwarf planet, after it was considered as the ninth planet since its discovery.[1]

A plutino is a trans-Neptunian object, that has the same orbital period as Pluto, and also has the same 2:3 orbital resonance with Neptune that Pluto has.[2] They are basically large icy bodies that lie beyond the orbit of Neptune, in a region known as the Kuiper Belt.[2] While Pluto and Eris are two of the larger known objects in this region, there are hundreds of objects within the Kuiper Belt that share these properties, and can also be considered as plutinos as well.[2]

 

[1] http://www.space.com/43-pluto-the-ninth-planet-that-was-a-dwarf.html

[2] http://www.icr.org/article/8019

[3] http://www.space.com/19824-clyde-tombaugh.html

[4] http://www.britannica.com/EBchecked/topic/598927/Clyde-W-Tombaugh

[5] http://www.britannica.com/EBchecked/topic/349831/Percival-Lowell

[6] http://www.britannica.com/EBchecked/topic/465234/Pluto/54311/Discoveries-of-Pluto-and-its-moons

[7] https://www.iau.org/public/themes/pluto/

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ASTB03 – Assignment 3 – Isaac Newton

Isaac Newton was an English physicist and mathematician, who also excelled in many other branches of science as well. He was the author of the Principia Mathematica, which is considered to be one of the most important texts in modern history. One of his biggest breakthroughs was, proving that a planet obeying the inverse square law must travel in an elliptical orbit, leading to his discovery of the Universal Gravitational Law. Newton wanted to know how the planets moved through space in the solar system, and this was a starting point for him creating his Laws of Motion. Newton came up with a thought experiment where a cannonball shot out of a cannon would travel in a straight line, but a force acting on it would cause it to fall to the ground. Newton realized that a stronger shot would cause the cannonball to travel farther, before it fell to the ground. He concluded that if the cannonball was shot fast enough, it would be able to travel all the way around the earth, and settle into an orbit around the planet. The reason that this breakthrough was so important was because it allowed Newton to conclude that all objects in the solar system followed these laws.

Newton had first been asked by English astronomer and mathematician, Edmond Halley, who is known for calculating the orbit of Halley’s comet, and helping to publish the Principia Mathematica, about the orbit of objects that satisfied the inverse square law, when he visited Newton at Cambridge. Newton told him that the shape was an ellipse, and that he knew that because he had already calculated it. He did not have the proof on hand right away and told Halley that he would send it to him later, which led to his eventual breakthrough mentioned above.

Halley had first had a conversation a few months earlier with Christopher Wren and Robert Hooke about the same topic. Wren was an English designer, astronomer, and architect, who had designed St. Paul’s Cathedral, while Hooke was a very highly regarded English physicist, who had many accomplishments across different fields. They had originally come to the conclusion that the shape of the orbits would be an ellipse, but did not have a solid proof, so Wren challenged them to come up with one within the following months. Hooke claimed he had a proof that the shape of the orbit would be an ellipse, but he would wait a little while before showing it. However, months had passed and there was still no proof. This is when Halley decided to visit Cambridge later that year to speak to Newton and ask his opinion on the matter. Newton was never too fond of Hooke for various reasons throughout the years. Later, after Newton’s proof became more public, Hooke had wanted some of the credit for the inverse square law to explain the motion of planets that Newton had proved when Halley had asked about the shape of the orbits. This of course, did not go over well with Newton, and just added to the list of things that Newton did not necessarily like about Hooke. The idea of the inverse square law was not necessarily a new one, and was a somewhat popular topic in science at the time, so it is entirely possible that Hooke might have had a major contribution to the proof, but Newton did not give Hooke credit.

Robert Hooke was not the only person that Newton had issues with over who deserves credit for an ideas. He also had issues with Gottfried Wilhelm Leibniz, over who had come up with the ideas for calculus. Leibniz was accused of plagiarizing parts of Newtons work when he published his own finding about calculus. Leibniz had “discovered” his version of calculus and published it. Newton would publish his ideas after Leibniz, but evidence existed that showed that Newton created these ideas earlier than Leibniz. It was known that Newton and Leibniz communicated regularly and many believed that it was Newtons work that helped Leibniz understand calculus. The Royal Society was in charge of deciding whether Leibniz had plagiarized Newton, who at the time was the President of the Royal Society, and had many supporters there. Over the years, Newton had discussed much of his work with those same supporters, which made it much easier for them to side with him. The Royal Society decided the Leibniz had plagiarized parts of Newtons work, and Newton was given credit for the discovery of calculus. Even with that decision, mathematics around the world had embraced the notation that Leibniz had used, except for England, who only taught Newtons work. It stayed this way for over 100 years, when England acknowledged work from outside the country and began teaching those as well.

In my opinion, both the person who discovered something, and the person who managed to prove it should be given credit for it. I think that it is extremely difficult to make any kind of discovery, and if someone manages to discover something, they should be rewarded for that. At the same time, it is also just as difficult to prove something, so if someone can formulate a proof, then they should also be credited for that. In the case of Newton and Leibniz, I think that if there is enough evidence to show that both had put in their own work on the topic, then both should be given some credit, since both of them had done the work around the same time.

Links Used:

Youtube link in assignment description

http://www.britannica.com/EBchecked/topic/413189/Sir-Isaac-Newton

http://www.britannica.com/EBchecked/topic/252812/Edmond-Halley

http://www.britannica.com/EBchecked/topic/649414/Sir-Christopher-Wren

http://www.britannica.com/EBchecked/topic/271280/Robert-Hooke

https://thonyc.wordpress.com/2011/09/28/the-man-who-inverted-and-squared-gravity/

http://starryskies.com/articles/spec/hooke.html

http://www.pbs.org/wgbh/nova/newton/principia.html

http://quantumaniac.com/post/18910018040/newton-v-leibniz-the-calculus-controversy-in

http://www.angelfire.com/md/byme/mathsample.html

http://www-history.mcs.st-and.ac.uk/Extras/Bossut_Chapter_V.html

https://royalsociety.org/events/2013/newtons-principia/

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ASTB03 – Assignment 2 – Copernicus

copernicusNicolaus Copernicus (Mikolaj Kopernik) was born in Torun, Poland. In his early life he had studied mathematics,
but later became interested in astronomy as well. While studying astronomy, he would eventually write Commentariolus
where he would explain his reasoning behind his belief of the heliocentric model. He also wrote De revolutionibus orbium
coelestium, which was banned by the catholic church because it was contrary to what was believed at the time. Some of his most important findings was that the earth spun on it’s axis, and that there was a large distance to the background stars, which was why they appear motionless; the earth actually orbited the sun and was not the centre of the universe, and that the sun was “motionless” at the centre of the planetary system.

One of the counter arguments to the earth spinning around it’s axis was that there would always be high winds
from east to west due to it’s rotation. Copernicus, however, said that as long as the air rotated in the same
direction and at the same speed as the earths rotation, then there would be no constant high winds. He noted that
the earths roation is what made the stars look like they moved

He also said that the distance that the earth travelled was only a fraction of the distance to the stars in the sky,
and thus the movement of those stars couldn’t be measured. This explained why those stars were “motionless” in the sky.
Motionless meaning that the positions of the stars did not change.

This stellar parallax argument is what critics tried to use as a counter example to the earth rotating around the
sun. They felt that if it were true, then the universe would be too large. Also, by having the earth rotate the sun,
the retrograde motion of some of the planets could be explained by saying that the retrograde appearence was a result
of the earth passing that planet. This made for a much simpler model than Ptolemy’s model and got rid of the need
for the epicycles used to explain the planets movements in the geocentric model.

Copernicus was also able to explain the varying brightness of the planets by placing the sun at the centre of
his system. In his model, since the earth is not at the centre, the other planets end up being different distances
away from the earth, which in turn causes the different brightness. If the earth had been at the centre, then the
brightness of the planets would not vary as much.

For these reasons, Copernicus felt that the geocentric model which was the commonly accepted model at the time, was
not correct, and that the heliocentric model, with the sun at the centre of the “universe” was the correct model.

While Copernicus was the first person to provide a model of a heliocentric model, he was not the first to have the
idea that the earth was not at the centre of the “universe”. Greek philosopher Pythagoras believed that the earth
“travelled around the sun”. Heracleides was another Greek philosopher, who figured out that Mercury and Venus rotated
around the sun. Aristarchus was a Greek astronomer who believed that the earth rotated on it’s axis and around the
sun, and also calculated sizes for the sun and the moon.

In my opinion, I feel that Copernicus’ most important statement was that the sun was at the centre of the planetary
system, and not the earth. While there were others that had this thought before him, none were able to really convince
anyone at the time that the earth was not at the centre. Copernicus managed to convince a few others with his models,
and while there were still many critics, his ideas would eventuall lead to the heliocentric model becoming the accepted
model over the geocentric one. It is also important because of the time in which Copernicus lived. Since the church
and many scholars at the time supported the geocentric system, it would’ve been very difficult to convince them
otherwise, but Copernicus’ models gave better explainations of how the planets and distant stars behaved, which in turn
laid the groundwork leading to the change from the geocentric belief to the heliocentric belief.

While he died before the heliocentric model became truly accepted, his findings would help in paving the way for
ancient astronomy to move forward.

Links Used:

http://www.biography.com/people/nicolaus-copernicus-9256984#synopsis

http://csep10.phys.utk.edu/astr161/lect/retrograde/copernican.html

http://scienceworld.wolfram.com/biography/Copernicus.html

http://www.studentpulse.com/articles/533/copernicus-galileo-and-the-church-science-in-a-religious-world

http://www.nmspacemuseum.org/halloffame/detail.php?id=123

http://www.polaris.iastate.edu/EveningStar/Unit2/unit2_sub2.htm

http://starchild.gsfc.nasa.gov/docs/StarChild/whos_who_level2/copernicus.html

http://www.scienceclarified.com/dispute/Vol-2/Historic-Dispute-Is-Earth-the-center-of-the-universe.html

http://iie.fing.edu.uy/ense/asign/hciencia/trabs2001/victor/docs/ScientRev.html

http://www.universetoday.com/33113/heliocentric-model/

http://www.britannica.com/EBchecked/topic/262434/Heracleides-Ponticus

http://www.britannica.com/EBchecked/topic/34377/Aristarchus-of-Samos

Picture from: http://cp91279.biography.com/Bio_Mini-Bios_Copernicus_SF_HD_768x432-16×9.jpg

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ASTB03 – Assignment 1 – Eratosthenes and the size of the Earth

Eratosthenes was a Greek scientist who was born in Cyrene, Libya around 276 BC and died around 194 BC. He was very knowledgeable in various subjects such as mathematics, geography, philosophy, and astronomy. However, he was never really considered to be at the top of any field in particular. Even though he was never considered to be at the top of any specific field, he was able to become the Director of the Library of Alexandria.

Eratosthenes accomplished many different scientific achievements throughout his life. He created maps which included what we would now call today the longitude and latitude lines. Another map he created was the route of the Nile River to Khartoum. Also, with regards to the Nile, Eratosthenes was one of the first people to give a correct explanation as to why the Nile flooded, his reason being that there was heavy rainfall at the source of the river, which in turn led to the flooding that occurred downstream.

Another one of his achievements include creating a timeline of scientific and political events after the siege of Troy. He also is credited with the invention of the discipline of Geography, while he was the Director of the Library of Alexandria.

There are a couple of achievements that Eratosthenes accomplished that he is most known for. The first is in the field of mathematics, called The Sieve of Eratosthenes. The Sieve of Eratosthenes is a logical method which can be used to find the prime numbers up to any given number. It was an important theory at the time, and while not the exact same, it is still a very important method in Number Theory today.

The second major accomplishment that Eratosthenes is commonly known for is that he was able to accurately measure the size of the Earth. While as the Director of the Library of Alexandria, Eratosthenes learned that in Syene(today known as Aswan), at noon during the summer solstice, no buildings cast shadows. He also noticed that in Alexandria, at the same time, the buildings there did cast a small shadow. He first had to make two assumptions. The first assumption he made was that the earth was spherical and the second assumption he made was that the sun was far enough away from the earth that the suns rays were parallel when they reached the earth. With those assumptions, he then measured the angles of the shadows of the buildings in Alexandria. Knowing the approximate distance between Syene and Alexandria, as well as the approximate angle of the shadows that the buildings were casting, which was measured to be approximately 7 degrees, Eratosthenes figured out that the angle measured was about one fiftieth of a full circle, and thus, the distance between Syene and Alexandria represented approximately one fiftieth of the circumference of the earth. With that, he then multiplied the distance between Syene and Alexandria by 50 to get the approximate value of the circumference of the earth.

The value calculated by Eratosthenes was approximately 250000 stadia. The precision of this value has been debated due to the fact that the exact value of a stadia has been debated. Due to the uncertainty of the stadia, the accuracy of the value calculated by Eratosthenes was said to be anywhere within 1%-30%.

I think the calculation was a success because of how accurate the value in the end was to what we know the actual size of the earth is. It was also a success because Eratosthenes needed to make assumptions that, at the time, were not obvious, such as the suns rays being parallel when it reached the earth and the earth itself being spherical.

As we can see, Eratosthenes accomplished many things that have gone on to become important stepping stones to many things that we now know today.

Links Used in this Post:

http://www.britannica.com/EBchecked/topic/191064/Eratosthenes-of-Cyrene

http://www-history.mcs.st-and.ac.uk/Biographies/Eratosthenes.html

http://www.famousscientists.org/eratosthenes/

https://sites.google.com/site/whoinventedgeography/

http://geography.about.com/od/historyofgeography/a/eratosthenes.htm

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