Hubble Space Telescope

Until the late twentieth century, astronomers could only observe the heavens with Earth-based instruments. Although many observatories across the globe contained some of the most advanced equipment with the farthest optical scope, a space-based telescope could capture images with far greater benefits. In space, noise interference and atmospheric blurriness have no distorting effect; in space, a telescope can capture farther and fainter objects than any telescope on Earth. [1] Above the Earth's atmosphere, light can be gathered at a much greater rate and accuracy, with much more detail and at significantly farther distances. Thus, even with a rather small 2.4-meter mirror, the Hubble Space Telescope revolutionised astronomical imaging upon its launch into the cosmos. [2]

The first space telescopes were imagined soon after the conclusion of the Second World War. It is believed that Lyman Spitzer's report in 1946 laid the foundations for the eventual launch of a space telescope. Almost half a century later, the Space Shuttle Discovery carried its precious cargo into space. Named after Edwin Hubble, the greatest American astronomer of the twentieth century, the Hubble Space Telescope left its earthly plane on 24 April 1990. [3]

Of course, the Hubble Space Telescope was not without severe faults prior to and following its launch. It was delayed at least half a decade by the tragic disaster of the Challenger explosion in 1986. However, the Challenger disaster proved to be a benefit for the preparation of the Hubble Space Telescope. Rather than rushing it into space, recalculations and upgrades could be made to its equipment. [4] One of the most pressing issues however concerned its main mirror which was erroneously grounded. Even an aberration of a thousandth of an inch disrupted the image-gathering capabilities of the telescope. Rather than focusing all of the light into its core, the off-mounted mirror cast a 'halo' of light around the core - enough to minimally distort the pictures being taken. [5] With other mechanical problems after its launch, NASA was forced to send a mission in 1993 (and another in 1997) to correct its issues. Though costly and rife with political antagonism, the missions proved successful and the Hubble Space Telescope has been able to capture the most incredible images from across the universe. [6] In its first eight years of operation alone, the Hubble Space Telescope had, in its orbit around Earth, travelled farther than the distance to Saturn, and transmitted billions of bytes of data. [7]

The Hubble Space Telescope is not designed much differently from its Earth-based counterparts. A large main mirror condenses light into a smaller secondary mirror, which is reflected back through a hole in the centre of the main mirror. The light gathered here is captured with the telescope's instruments, all of which are fitted with electronic cameras (CCDs) to transmit the information to Earth. Electric currents produce pixellated images on computers, which can also be manipulated with imaging techniques like colouring, contrast, and imposition. [8] There are some features of the Hubble Space telescope that are different from Earth-based telescopes, including panels to generate solar energy for the telescope's instruments and a magnetometer for detecting the Earth's magnetic field. [9]

The Hubble Space Telescope has done great things for astronomy. Just some of its many accomplishments include measuring star clusters to determine the age of the universe, observing supernovae to aid the theory of a rapidly-expanding universe, detecting the presence of other solar systems, and studying our own Solar System's planets and moons:

"The pictures sent back from Hubble have, really for the first time, brought home

to ordinary people the immensity of the forces at work in the heavens. We have

seen the effect of comets smashing into the surface of Jupiter with an explosive

power of 100 million megatons; watched storms brewing on the surface of

Saturn; witnessed doomed stars exploding amid brilliant fireworks displays, with

loops and rings of gas light-years across surging outwards into space; black holes,

white dwarfs, red giants... all have been revealed." [10]

Two of the Hubble Space Telescope's greatest observations are of a distant redshift 6.8 galaxy which, along with the Spitzer Space Telescope, could estimate its age and mass, and in 2002 and 2003, observations of the Andromeda galaxy determined that it had collided with one or more galaxies billions of years ago, distributing billions of stars into an awesome halo. [11]

Eventually, the Hubble Space Telescope will fail to serve its purpose. This can happen in at least two ways: either the instruments on the telescope are fatally damaged or cease to operate effectively, or it's image-capturing capabilities are deemed obsolete. Most likely, the the U.S. government will determine that its maintenance is too costly to continue servicing and will terminate the project. [12] One option is to simply shut the machine down, but the risk of it crashing down to Earth is far too great. Instead, NASA has discussed sending a satellite to either lift the Hubble Space Telescope to a safer orbit or bring it back down to Earth. The latter option seems to be a more desirable one, as the effect of space on a great machine could be studied and its body housed in a museum. [13]

No other instrument in the history of astronomy since Galileo's first telescopes has done more to advance scientist's understanding of the universe so quickly. [14] For over twenty years, the Hubble Space Telescope has generated millions of outstanding images and introduced astronomy to the greater public. Now, more than ever, the universe can be viewed by anyone with even a remote interest in space. Thus, he Hubble Space Telescope has proven to be one of the great moments in astronomy.

Notes:

[1] Fischer, Daniel, and Hilmar W. Duerbeck. Hubble: A New Window to the Universe. New York: Copernicus, 1996, p. 26.

[2] Kanipe, Jeff. Chasing Hubble's Shadows: The Search for Galaxies at the Edge of Time. New York: Hill and Wang, 2006, p. 5.

[3] Clark, Stuart. Universe in Focus: The Story of the Hubble Telescope. London: Cassell, 1997, p. 12.

[4] Leverington, David. New Cosmic Horizons: Space Astronomy from the V2 to the Hubble Space Telescope. Cambridge, UK: Cambridge University Press, 2000, pp. 431-2.

[5] Petersen, Carolyn C, and John C. Brandt. Hubble Vision: Further Adeventures with the Hubble Space Telescope. Cambridge: Cambridge University Press, 1998, p. 9; Clark, Universe in Focus, p. 16.

[6] Petersen & Brandt, Hubble Vision, p. 9.

[7] Fischer, Daniel, and Hilmar W. Duerbeck. Hubble Revisited: New Images from the Discovery Machine. New York: Copernicus, 1998, p. 185.

[8] Clark, Universe in Focus, p. 14, 23-4.

[9] Petersen & Brandt, Hubble Vision, p. 14.

[10] Wilkie, Tom, and Mark Rosselli. Visions of Heaven: The Mysteries of the Universe Revealed by the Hubble Space Telescope. London: Hodder & Stoughton, 1998, p. 13-15.

[11] Kanipe, Chasing Hubble's Shadows, pp. 38, 148.

[12] Kanipe, Chasing Hubble's Shadows, p. 5.

[13] Fischer & Duerbeck, Hubble Revisited, p. 191.

[14] Kanipe, Chasing Hubble's Shadows, p. 5.

References:

Clark, Stuart. Universe in Focus: The Story of the Hubble Telescope. London: Cassell, 1997.

Fischer, Daniel, and Hilmar W. Duerbeck. Hubble: A New Window to the Universe. New York: Copernicus, 1996.

Fischer, Daniel, and Hilmar W. Duerbeck. Hubble Revisited: New Images from the Discovery Machine. New York: Copernicus, 1998.

Kanipe, Jeff. Chasing Hubble's Shadows: The Search for Galaxies at the Edge of Time. New York: Hill and Wang, 2006.

Leverington, David. New Cosmic Horizons: Space Astronomy from the V2 to the Hubble Space Telescope. Cambridge, UK: Cambridge University Press, 2000.

Petersen, Carolyn C, and John C. Brandt. Hubble Vision: Further Adventures with the Hubble Space Telescope. Cambridge: Cambridge University Press, 1998.

Wilkie, Tom, and Mark Rosselli. Visions of Heaven: The Mysteries of the Universe Revealed by the Hubble Space Telescope. London: Hodder & Stoughton, 1998.

Pluto

Pluto is one of several million objects lying in an outer layer of small icy rocks on the edge of our Solar System, in the Kuiper Belt region. Most of these Kuiper Belt Objects (KBOs) have solid silicate cores with several layers of ice near and at the surface. Pluto may contain ammonia and methane ice as well. [1] Recent observations of Pluto also suspect levels of nitrogen and carbon monoxide, and possibly a gaseous, albeit thin, atmospheric layer. [2]

Pluto and Mercury, as the smallest planets* and as the furthest and closest planets to the Sun, respectively, have orbits with the least approximate circular motion. As we have come to understand in class on the laws of motion pertaining to astronomical bodies, Pluto's revolutions are some of the slowest in the Solar System, being one of the furthest objects from the Sun, taking nearly 250 (Earth) years to complete a single orbit. [3] What is interesting about Pluto here is that it rotates sideways to other planets (as does Uranus). [4]

Pluto has three moons. The largest of these, Charon, was discovered in 1978 and is large enough (about half the size of Pluto) that Pluto-Charon was the first double planet in the Solar System. [5] 

The following table gives some basic information on Pluto's characteristics [6]:

	Pluto	Earth	Relativity (Pluto-Earth)
Diameter (mean)	2280 km	12 740 km	0.179
Distance from Sun	5.9 billion km	149.6 million km	39.5
Surface temperature (Kelvin)	50	260-310	N/A
Mass	0.078 x 10²⁴ kg	5.98 x 10²⁴ kg	0.013
Mean density	2048 kg m⁻³	5520 kg m⁻³	0.371

American astronomer Clyde Tombaugh discovered Pluto in 1930, basing his search for the ninth planet on previous predictions established by Percival Lowell. Lowell had assumed that the gravitational motions of Uranus and Neptune were being affected by a massive object that lay beyond the two planets. That 'massive object' was thought to be Pluto. It was only after its discovery about thirty years later at the observatory which bore his name - the Lowell Observatory in Arizona - that it was realised that due to its small size, Pluto could not have had such a dramatic effect on Uranus's and Neptune's motions. In retrospect, Lowell's prediction was baseless, and can best be explained by faulty measurements. [7] It did, however, establish the beginning of a search for what lay on the outer reaches of our Solar System.

Continuous exploration and scientific discoveries in this part of the Milky Way have led to changing theories and debates regarding Pluto's status. In 2006, the International Astronomical Union (IAU) recategorised Pluto as a dwarf-planet, demoting it from the other eight planets in the Solar System. This ruling deemed that a planet must be spherical and orbit the Sun - two classifications which Pluto fits - but also be in a space free of cosmic objects. As stated above, Pluto is within the Kuiper Belt - a large swath of objects similar to an asteroid belt. Therefore, Pluto was considered unfit to hold full planetary status. In 2014, a debate amongst three of the most established astronomers in the world, Owen Gingerich, Dimitar Sasselov, and Gareth Williams, showcased a public decision at the Harvard-Smithsonian Center, in which a popular majority 'voted' to re-instate Pluto's planetary status to full membership. [8]

"Found in the inner parts of the Kuiper Belt, plutinos are Kuiper Belt objects {KBOs) that have orbital periods very similar to that of Pluto. Their orbits are stabilised against gravitational perturbations by the 3:2 mean-motion resonance with Neptune, meaning that they orbit the Sun twice for every three orbits of Neptune." [9]

This summer, NASA's New Horizons mission will reach Pluto - the farthest any object from Earth has been - and is sure to teach us new things about what lies on the peripheries of our Solar System.


End Notes:

[1] Roger Smith (Editor). (1998). The Solar System (Vol. 3). Pasadena, CA: Salem Press, 887.

[2] "Pluto". (n.d.). In Royal Museums Greenwich - National Maritime Museum: http://www.nmm.ac.uk/explore/astronomy-and-time/astronomy-facts/solar-system/pluto.

*- The planetary nature of Pluto has been disputed, as will be examined further in this post. From this source, Pluto is still considered a planet in our Solar System.

[3] Keith Holliday. (1999). Introductory Astronomy. Chichester, England: John Wiley & Sons, 90-1.

[4] Holliday, Introductory Astronomy, 65-6.

[5] "New Horizons: The First Mission to Pluto and the Kuiper Belt: Exploring Frontier Worlds." (January 2006). NASA: http://www.nasa.gov/pdf/139889main_PressKit12_05.pdf.

[6] Holliday, Introductory Astronomy, 67 [Table 5.2; calculations for Pluto are my own].

[7] Blondel, Philippe, and John W. Mason (Editors). (2006). Solar System Update. Chichester, England: Praxis Publishing, 267; "Pluto", National Maritime Museum; "Celestial Mechanics - Planetary Perturbations." (n.d.). Retrieved from http://science.jrank.org/pages/1295/Celestial-Mechanics-Planetary-perturbations.html.

[8] "Pluto", National Maritime Museum; Jennifer Hackett. (February 13, 2015). "Pluto's ongoing identity crisis stirs planet definition debate." In Scienceline: http://scienceline.org/2015/02/plutos-ongoing-identity-crisis-stirs-planet-definition-debate/.

[9] "Plutinos." (n.d.). In Cosmos - The SAO Encyclopedia of Astronomy. Swinburne University of Technology: http://astronomy.swin.edu.au/cosmos/P/Plutinos.


References:

"Celestial Mechanics - Planetary Perturbations." {n.d.). Retrieved from http://science.jrank.org/pages/1295/Celestial-Mechanics-Planetary-perturbations.html.

"New Horizons: The First Mission to Pluto and the Kuiper Belt: Exploring Frontier Worlds." (January 2006). NASA: http://www.nasa.gov/pdf/139889main_PressKit12_05.pdf.

"Plutinos." (n.d.). In Cosmos - The SAO Encyclopedia of Astronomy. Swinburne University of Technology: http://astronomy.swin.edu.au/cosmos/P/Plutinos.

"Pluto". (n.d.). In Royal Museums Greenwich - National Maritime Museum: http://www.nmm.ac.uk/explore/astronomy-and-time/astronomy-facts/solar-system/pluto.

Blondel, P., & Mason, J.W. (Editors). (2006). Solar System Update. Chichester, England: Praxis Pubishing.

Hackett, Jennifer. (2015, February 13). "Pluto's ongoing identity crisis stirs planet definition debate." In Scienceline: http://scienceline.org/2015/02/plutos-ongoing-identity-crisis-stirs-planet-definition-debate.

Holliday, Keith. (1999). Introductory Astronomy. Chichester, England: John Wiley & Sons.

Smith, Roger (Editor). (1998). The Solar System (Vol. 3). Pasadena, CA: Salem Press.

Universal Gravitation and Discovery Disputes

The work of Galileo had set in motion a new Scientific Revolution. Science and reason became fundamental cornerstones of the study of a natural world only before thought of philosophically. Empiricism - mathematical theory - would accommodate observation in the pursuit of new scientific discoveries. [1]

It has been argued by scholars that previous work done by Johannes Kepler was instrumental in the later discoveries of gravity and planetary motion expounded by the British scientist, Isaac Newton. However, although Kepler's laws regarding traditional astronomy were unprecedented, "few astronomers adopted them. There was no Keplerian cosmology or world system as there was Ptolemaic, Copernican, and Tychonic world systems. In many ways, Kepler's work was a historical dead end." [2]

Newton's now infamous epiphany was said to have occurred in the apple orchard of his family home. There under a tree, Newton is said (indeed, he told the story himself in his elder years) to have witnessed an apple falling, and the force of gravity was theorised. As one scholar (comically) noted however, "I'm extremely skeptical about the role of fruit in Newton's life." [3] Fable or not though, Newton's observations and experiments with gravitational force led to the simplification of motions, like velocity and acceleration. More importantly, "it was possible to calculate quantities that are constantly changing.... With this technique, Newton invented an entirely new branch of math called calculus." [4]

Newton also constructed a new and more compact version of a telescope. His refracting telescope, as the instrument is known, is the model used for contemporary telescopes used to peer into the deepest reaches of the visible universe. For Newton, the development served as a launching pad for his scientific career: "It brought Newton on to the world stage of science, and Newton became an overnight sensation." [5]

The greatest work attributed to Newton stems from a visit with the astronomer Edmond Halley. Halley, an astronomer who had studied at Oxford University, analysed the heavens from his colonial workspace on the South Atlantic island of St. Helena, and the most famous comet is named after him. Halley was a prognosticator of planetary orbits and transits, and therefore, an accomplished astronomer to discuss similar work with Newton. [6] During their meeting, Newton surprised Halley by explaining that ellipses formed the line of planetary motion. Though he could not provide documentation of his theory to Halley at the time, Newton devised a rule known as the 'inverse square law' to define this relationship in the heavens. Years of Newton's observations, experiments, and discoveries were published in a book, the Principia, soon after. "It is the most magnificent work, it is the most all-encompassing work, it is the most daring book of any scientific treatise ever written." [7] Within its pages, Newton outlined his three laws of motion, and within these laws, it was evident that the same gravitational forces on Earth operated in space as well: "Newton's breakthrough was to see that the Moon's orbit around the Earth and a cannonball's motion on Earth were governed by the same law of gravity." [8]

"It's so important because it really tells us how nature operates in a fundamentally new way. Newton

is saying, 'the same thing that is going on in the heavens is going on on Earth, and vice versa.' It gives

us a guidebook to answer the age-old question of what causes the rise and fall of the tides. It gives

us answers to the orbits of the planets and their positions. It's a tremendous act of intellectual triumph,

one of the great keystone, cornerstone pieces of our intellectual heritage." [9]

Newton's discovery of gravitation laid the foundation for modern science and the ways in which we humans perceive our place in the universe.

Of course, Newton was not without his critics. His rivalry with fellow scientist (and Royal Society member) Robert Hooke may not as well publicised today, but it was a constant stress for Newton to be exposed to criticism. "As soon as the Principia was published, Newton's old rival, Robert Hooke, claimed he had come up with some of the key ideas first. And later, others attacked it because Newton did not explain what gravity is, just how to calculate its strength." [10] Throughout his life, Newton was never entirely comfortable with publicising his works for fear of shame, ostracising, and negative reaction. [11]

Newton's primary challenge was of the ideas of Rene Descartes, a French philosopher who thought of the universe as a giant machine. Descartes argued that all universal motion was simply "the physical interactions of parts of this machine." [12] For much of the eighteenth century, the theories on physics put forth by Descartes and Newton were the main doctrines for evaluation. The use of different methodologies to come to a respective conclusion may explain part of the divide between British and European science in the second half of the 1700s: "Newton's loyal followers in England made little progress compared to scientists on the continent less tightly tied to geometrical proofs and more ready to take up algebraic methods (developed by Descartes)." [13]

Newton was also fiercely engaged in a copyright battle with the German mathematician and philosopher Gottfried Leibniz, who had also claimed to have invented calculus. Leibniz was a staunch supporter of Descartes' theories on planetary motion, and pitted the two on a fundamental war of physics: vortices vs. elliptical orbits. Leibniz argued that gravity was the result of revolving vortices around the Earth. [14]

Contrary to modern opinion, Newton was not a fervent opponent to the idea of a universe operating under the guise of an omnipotent and omnipresent being. As a member of Trinity College, Newton was expected to pursue theology and work as a Church representative at the University of Cambridge. It was not until a century later that "gangs of interpreters (most of them French) will take the 'God' out of Newton's world." [15] Perhaps this was part of the schism between British science and Continental science in the years following Newton's discoveries. As Newton maintained the idea of a universe with God in it, French and German scientists (like Descartes and Leibniz) attempted to explain a 'godless' universe in the latter years of the Enlightenment.

Another important figure during this time was Christopher Wren, a famous architect from the UK who also had a keen mind for astronomy. Educated at Oxford University, Wren discussed space and the planetary motions with Newton as early as 1677. Wren however, like Hooke, did not possess the mathematical acumen "or geometrical ability to show what orbit would result from an inverse square force of attraction: in effect, to derive Kepler's laws of planetary motion from principles of dynamics." [16]

In my opinion, scientific theories must be documented, tested, and verified multiple times by many reputable contemporaries before they can be recognised as 'discoveries'. This is why we have the 'scientific method' as a process of analysis. It legitimises the work of scientists and allows for the transparent circulation of their ideas amongst the intellectual community and the public at large. Of course, all sorts of problems can and will likely persist - from the destruction of evidence, to accusations of plagiarism, to conflicting research and ethical concerns. All of these possibilities are likely to occur as the work of scientists continues (and some could say, intensifies) in the social, economic, and political arenas of our global world. In Newton's time, these difficulties were even more problematic, as information was not as readily communicable and scientists could be threatened with heresy and put to the death (of course, this can still happen!) As a historian however, it is important to have documented proof of claims so that discoveries can be analysed fairly and attributed to their rightful 'owners'. Therefore, I believe in the scientific method as a necessary process.


End Notes:

[1] Chris Oxley (Director). Smith, George (Dibner Institute) (Contributor). (2005). Newton's Dark 
Secrets [YouTube video]. USA: PBS/Nova.

[2] Norriss S. Hetherington. (2006). Planetary Motions. Westport, CT: Greenwood Press, 148.

[3] Oxley (Dir.). Schaffer, Simon (University of Cambridge) (Contr.). Newton's Dark Secrets.

[4] Oxley (Dir.). Abraham, Murray F. (Narrator). Newton's Dark Secrets.

[5] Oxley (Dir.). Speaker unknown. Newton's Dark Secrets.

[6] Hetherington, Planetary Motions, 155: "Halley died before the predicted return of his comet in 1758. He also died before the predicted transits of Venus in 1761 and 1769, abut he left detailed instructions for calculating the size of the solar system from their observation."

[7] Oxley (Dir.). Christianson, Gale (Newton biographer) (Contr.). Newton's Dark Secrets.

[8] Oxley (Dir.). Abraham (Narr.). Newton's Dark Secrets.

[9] Oxley (Dir.). Christianson (Contr.). Newton's Dark Secrets.

[10] Oxley (Dir.). Abraham (Narr.). Newton's Dark Secrets.

[11] Oxley (Dir.). Newton's Dark Secrets.

[12] Oxley (Dir.). Abraham (Narr.) Newton's Dark Secrets.

[13] Hetherington, Planetary Motions, 165-66.

[14] Hetherington, Planetary Motions, 165.

[15] Oxley (Dir.) Schaffer (Contr.) Newton's Dark Secrets.

[16] Hetherington, Planetary Motions, 152.


References:

Hetherington, Norriss S. (2006). Planetary Motions. Westport, CT: Greenwood Press.

Oxley, Chris (Director). (2005). Newton's Dark Secrets [YouTube video]. USA: PBS/Nova. Narrated by Murray F. 
Abraham. https://www.youtube.com/watch?v=7n3RWAIlzAI.

Copernicus

In his most famous book De Revolutionibus, Nicolaus Copernicus argued that the Sun, not the Earth, was the centre of the universe. Printed in 1543, his heliocentric view of the solar system argued against nearly 2000 years of entrenched scientific theory, and proved to be the most important Copernican thesis. As this post will show, the Sun as the centre was a even more revolutionary idea for human comprehension than it was for astronomical precision.

That Copernicus was the first to interpret the universe as revolving around the Sun, or that the Earth spun on its own axis were not brand new ideas. Jean Buridan (c. 1300-1358), Nicole Oresme (c. 1320-1382), and Nicholas of Cusa (1401-1464) were all medieval polymaths who had developed a diurnal conception of the Earth in the fourteenth and fifteenth centuries - before Copernicus's time - and even an ancient Greek astronomer, Herakleides, proposed such a theory. Another, Aristarchus of Samos, also believed in a heliocentric universe and a daily spinning Earth motion. It seemed far more plausible that the tiny Earth, not the gigantic universe around it, could rotate within a 24-hour period. Copernicus is such an influential figure in this field because he was the first to construct "a mathematical system of planetary motion from a heliocentric perspective." Though he (incorrectly) assumed that the Sun was stationary (his protege Johannes Kepler later corrected this view), "Copernicus was the first to develop a detailed account of the astronomical consequences of the Earth's motion." His system provided something that the long traditional Ptolemeic model did not - coherence. With Copernicus's heliocentric model, "the retrograde motions of the (inner and outer) planets become a natural consequence of the motion of the Earth around the (mean) sun" and the motion of the planets was uniform. Here, "Copernicus's solution is only partially successful because he still assumes uniform circular motion" but "the major irregularities of the planetary motions are only apparent. These appearances are produced by the orbital motion of the Earth. As the sun is stationary in the heliocentric system, it does not have retrograde motion" (Weinert, 21-5; Margolis, 87, 106 [note 10]).

Copernicus's model also enabled him to measure the distances between planets. Adopting mathematical methodologies used since antiquity and updated observations of planetary orbits, Copernicus could determine the relative distance of the planets from the Sun and from each other. 

[The Copernican Model of the Solar System; source: Google Images] 

Here again, we see a coherent system that could do away with the antiquated beliefs of celestial spheres. That being said however, Copernicus's observations did not totally disprove the ancient Greek astronomical observations nor, especially, Ptolemy's heavily entrenched geocentric model:

"The Greeks sought to fit the appearances they observed to their prior beliefs about celestial phenomena.

Copernicus claims that his work is based on long and numerous observations, his own and those of the

Greek tradition.... Nevertheless Copernicus's observations do not establish any new facts. The Copernican

observations do not go beyond the discoveries of the Greeks. They do not cast in doubt Greek

presuppositions about circular motion. It is therefore fair to say that from an observational point of view,

the Copernican and Ptolemaic systems were equivalent" (Weinert, 25).

Modern astronomers cannot disregard the observations and theories proposed by the ancient astronomers just because of the updated 'discoveries' of Copernicus, Kepler, and other more recent astronomers. For without Ptolemy's model to establish a 'base theory,' Copernicus could not have expanded upon those ideas and eventually develop his own model.

Explaining the season was another conundrum which the Greeks were aware of, but still required an astronomical model for comprehension. In a geocentric universe, the variations in weather and temperature which corresponded with the four seasons in a year could not be definitively explained. So Ptolemy, using observations by Hipparchus, devised a system with eccentric or displaced circles. At a 23.5 degree angle, the Sun would orbit the Earth on a tilt. Copernicus's model attained a more difficult theory concerning this phenomenon - a third motion, or "deflexion of the Earth's axis." Because the planets lay within celestial spheres (again, disproved by Kepler, who argued that astronomy could do "without the useless furniture of fictitious spheres and circles"), and moved as part of a system, the seasons and the length of days fit a symmetrical pattern (Weinert, 25-8).

Copernicus's theory of a heliocentric universe was fundamental to the establishment of a humanist approach to science. Although humans were no longer the centre of the universe, they could however apply a mathematical and geometrical methodology to rationalising the vast wonders of the cosmos. "By making Earth a planet, Copernicus revolutionized humanity's view of its place in the universe and triggered a controversy that would eventually bring the astronomer Galileo Galilei before the Inquisition."  To arrive at such a conclusion meant the opening of other radical ideas. It signified the beginning of a new scientific paradigm, displacing nearly 2000 years of entrenched astronomical thought. Simon Stevin, William Gilbert, Thomas Digges, Kepler and Galileo were all contemporary astronomers of Copernicus to encourage this new paradigm shift (Weinert, 1, 20; Backman, Seeds, et al, 53-4; Margolis 70]

A mobile Earth could naturally explain retrograde motions, the seasons, and the relative distance of planets from the Sun within a heliocentric universe. Thus, Copernicus's system proved to be another launching pad for further research and quantitative data on our solar system. More importantly, it fundamentally changed the way we humans viewed our place in the universe.

Sources:

Backman, Dana E, Michael A. Seeds, et al. Astro. Toronto: Nelson Education, 2013.

Margolis, Howard. It Started with Copernicus: How Turning the World Inside Out Led to the Scientific Revolution. New York: McGraw-Hill, 2002.

Weinert, Friedel. Copernicus, Darwin, & Freud: Revolutions in the History and Philosophy of Science. Chichester: Wiley-Blackwell, 2009.

Eratosthenes

Eratosthenes was truly a versatile figure - he may even be called a 'Renaissance Man'. Born in the third century BCE, Eratosthenes participated in astronomy, philosophy, and poetry and, in addition to a steep knowledge in mathematics, Eratosthenes was also a geographoi, or cartographic surveyor - perhaps one of the first of his kind. Being an academic however, he "rarely ventured into the field" to conduct his work (Talbert, 131). Also, his knowledge of the world's surface - though extensive and highly calculable at the time - "extended only as far as India" (Talbert, 199). 

Eratosthenes' greatest published texts were his Geographica, which "offered a rational and critical argument for the layout and content of a world map" (Talbert, 115) and Measurement of the Earth, which - as the title suggests - outlined Eratosthenes' model for determining our planet's circumference. Unfortunately, both texts no longer exist but we are aware of them through the later writings of Strabo and Hipparchus.

Geographers in the ancient world used a tool - called a dioptra - to measure distances using the stars, "just as was done later with the great medieval instrument that was its direct descendant, the astrolabe" (Talbert, 141). Europe, Africa and Asia were the only continental landmasses known to the Greeks during antiquity. In their maps, Europe and Africa represented the western hemisphere and Asia was in the eastern hemisphere, with the eastern Mediterranean located at the centre of the map. Though he only published a textual 'image' of his worldview, the map below symbolises what the Earth looked like to Eratosthenes and many of his contemporaries in the latter decades of the ancient era:

[Eratosthenes's world map, similar to the one seen on p. 103 of Akerman, Ancient Perspectives; image source: http://www.henry-davis.com/MAPS/Ancientimages/112A.JPEG via Google Images]

"Building on Dicaearchus's diaphragma and rejecting a division of landmasses only by bodies

of water, he [Eratosthenes] split the oikoumene into two equal halves, with a parallel from the

Pillars of Hercules to the easternmost limit of the Taurus Mountains; hence, Dicaearchus's

symmetrical axis was reinforced (Strabo 2.1.1). Eratosthenes then subdivided his northern

and southern halves into "seals," of sphragides, irregular quadrilateral shapes resembling

document seals. Thus, India was rhomboidal, bounded by oceans on two sides, by

the Taurus Mountains to the north and the Indus River to the west; Ariana was a parallelogram

delimited by the Caspian Sea, the capes of Carmania (in southern Iran), and the Persian Gulf.

Eratosthenes divided his northwest region, Europe, on the basis of three promontories projecting

into the Mediterranean: the Peloponnese, Italy, and the Ligurian "promontory" of Corsica

and Sardinia. Even though his excessive generalizations were later subjected to harsh

criticism by Hipparchus and Strabo, his sphragides still represent a concerted effort

to compartmentalize, categorize, and impose order on the oikoumene" (Talbert, 102-104).

Eratosthenes was the director of the library at the Museum of Alexandria. It was during this time that he conducted his research for Measurement of the Earth, which would prove to be Eratosthenes' greatest achievement. Though the measurements and calculations are far too mind-boggling for me to comprehend, his methodology was quite straightforward. To simplify, Eratosthenes was aware of a well in Syene (now Aswan, Egypt) which the sun would completely illuminate the bottom of (no shadow was cast) at noon during the summer solstice, when the sun was at its zenith. Determining that Syene was on the same meridian as his home in Alexandria, he observed that the sun cast a slight shadow in Alexandria at the same time on the same day. With this observation, and a calculation of the distance between Syene and Alexandria, he could hypothesise that the Earth was indeed spherical, and determine its circumference. Though his calculations were slightly inaccurate, they were nonetheless remarkably close to the measurements we now know today (Talbert, 100-102; "Size of the Earth: Eratosthenes, 200 BC": http://www.earth.northwestern.edu/public/seth/107/Time/erathos.htm; Chodos, "This Month in Physics History: June, ca/ 240 B.C. Eratosthenes Measure the Earth," http://www.aps.org/publications/apsnews/200606/history.cfm).

["Size of the Earth (Eratosthenes 200 BC)," image http://www.earth.northwestern.edu/public/seth/107/Time/Image1.gif;

source: http://www.earth.northwestern.edu/public/seth/107/Time/erathos.htm]

Eratosthenes' legacy in the field of geography and cartography lived on well into the Roman period, and indeed, lives on even today
(Chodos, http://www.aps.org/publications/apsnews/200606/history.cfm).

Sources:
"Size of the Earth (Eratosthenes 200 BC)": http://www.earth.northwestern.edu/public/seth/107/Time/erathos.htm.

Alan Chodos, ed., "This Month in Physics History: June, ca. 240 B.C. Eratosthenes Measures the Earth," American Physical Society 15:6 (June 2006): http://www.aps.org/publications/apsnews/200606/history.cfm.

Richard J.A. Talbert, ed., Ancient Perspectives: Maps and Their Place in Mesopotamia, Egypt, Greece and Rome. Chicago: The University of Chicago Press, 2012.