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Fariha Newaz
Phil 350
Ptolemy’s Rejection of the Motion and Location of Earth
Ptolemy followed the Aristotelian school of thought, which stated that the Earth remained motionless at the center of the Universe. However, some philosophers did believe that the Earth revolved around sun the sun while spinning on its axis daily instead. Ptolemy did not agree with this school of thought, so he gave arguments that rejected these notions. Despite Ptolemy’s rejection of this notion was incorrect, he wasn’t incorrect to mention his arguments because given what was known at the time and not having the ability to observe the location the motion of the Earth, it would have been hard to be convinced of this theory. No one could have seen the errors in Ptolemy’s arguments because his rebuttals were based upon observation or lack thereof, so others couldn’t point out he was wrong because they too couldn’t see these claims. 
Yes, the Earth is stationary, well according to Ptolemy it is. Ptolemy gave three main reasons as to why he rejected the notion that the Earth spun on its axis. His common sense argument consisted of two parts, in the first part he posed the question, if the Earth were moving, how come we couldn’t feel the movement? He is under the correct assumption that if indeed the Earth was moving, it would be moving at a very high velocity which would mean that the movement would have been felt. An example given by the Worldviews text that explains this argument, they state “if you are in a convertible moving 70 miles per hour down the interstate, there is no question in your mind that you are in motion,” (DeWitt 91) this analogy helps put into perspective Ptolemy’s first common sense argument, because motion on Earth can always be felt. His logic isn’t wrong in the sense that if the Earth is moving at a high velocity well then people on Earth, in theory, would feel it as well. However, the reason Earth’s speed isn’t felt is because the mass of a single person is significantly less relative to the mass of the Earth, so it would not be possible to feel the motion of an object as big as the Earth. The second common sense argument that was presented by Ptolemy was that if the Earth was indeed moving, then what was moving it? During this period of time, ancient philosophers didn’t know about gravity so it made sense for Ptolemy to question a mystery force which was nonexistent to them. These two arguments conclude Ptolemy’s “common sense” arguments as to why the Earth is not in motion. 
Along with his common sense arguments, Ptolemy had a second argument as to why the Earth doesn’t spin on its axis which had to do with the motion of falling objects. During this time, people thought that if the Earth were spinning on its axis, then that would mean falling objects would land behind of where they were dropped rather than falling perpendicularly to the Earth. The author called this the “common sense view of motion’ (DeWitt 93) which kind of puts into perspective Ptolemy’s thinking because it is the most common answer given by people even today. 
The third, and final, argument he made had to do with stellar parallax. In the book, it states that “Ptolemy notes that the ‘angular distances’ of the stars always remain unchanged,” (DeWitt 94) what he is essentially trying to say is that, if the Earth were moving then stellar parallax would be observed. Ptolemy had strong backing for this argument because he argued that since the Earth is moving at a high velocity then stellar parallax would have to be observed, which it wasn’t, therefore the Earth is not moving. However, Ptolemy’s argument relies on the distance of the stars, which at the time they thought were just a little past Saturn, when in fact the stars are much farther away. Assuming that the stars were as close as people during this time thought, stellar parallax would have definitely been observed, however since the stars are much further away than the ancients had thought, it makes sense as to why stellar parallax wasn’t observed until much later. Therefore, given the fact that Ptolemy was under the impression that the stars were much closer than they actually are his argument regarding stellar parallax and the Earth remaining motionless is on, Ptolemy’s argument for a stationary Earth was a strong one. 
Ptolemy provided three main arguments as to why he believed that the Earth was at the center of the universe. One of the arguments was of the motion of falling objects on the Earth. Since ancients believed that heavy objects fell perpendicular to the surface, it meant that the Earth had to be in the center. The second reasoning given was that it appeared to look like all the stars and planets revolved around the Earth, therefore from the perspective of Earth, it had to mean that it was at the center. The third argument had to do with the element earth, which is the heaviest element towards the center of the Earth. Since Earth is composed of this element and with the ancients believing that the heaviest objects gravitate towards the center, it was automatically assumed that the Earth lied in the center of the universe. Ptolemy’s arguments stemmed from what the ancients believed during this time therefore it is sensible that he provided these rationales. However, these arguments are considerably weaker than the ones provided for proving that the Earth is motionless. These arguments shed a light on the limited knowledge that the ancients had to work with when it came to identifying the location of Earth relative to the rest of the universe. 
The rationale Ptolemy’s provided as to why he rejected the idea of the Earth revolving around the Sun while spinning on its axis led to the conclusion that, yes, Ptolemy had good reasons for rejecting these ideas. Since, it was almost impossible to definitively prove the location and motion of the Earth through observation, so it would have been hard to convince anyone at that time. The science, specifically the physics, of that time didn’t account for gravity, if it had, then Ptolemy would have been wrong to reject these ideas because gravity is the answer to a lot of his main arguments. Along with the limited physics, the lack of technology, specifically a telescope, also made it hard to accept these notions because the actual distance of the stars could not be observed, making it hard to disprove Ptolemy’s stellar parallax argument. Since it was hard to observe these motions, it comes as no surprise that no one thought there was anything wrong with Ptolemy’s arguments. 
Ptolemy’s arguments for rejecting the notion that the Earth spins on its axis daily and revolves around the sun came from the fact that the motion of the Earth and its location could not be observed then. The inability for observation comes from the lack of technology and the physics during that time was in its earlier stages of trying to understand how everything worked. Therefore, it made sense that Ptolemy rejected these notions and why others couldn’t see the flaws in his arguments.