The point is if us “advanced” people don’t know the answer, why should the ancients know it?
Johannes Kepler actually disproved geocentrism only a few years before the telescope was invented. He used Tycho Brahe’s surprisingly precise naked eye observations of Mars’ and the Sun’s relative positions on the sky. He first proved that Ptolemy’s, Copernicus’ and Brahe’s Solar system models were all mathematically identical, they just chose different frames of reference. Then he painstakingly founded astrophysics and proved genuine heliocentrism.
A few points regarding this. Even if this is correct, your average person would not have the astronomical and mathematical skills to come up with the similar conclusion of Kepler. But I highly doubt Kepler “disproved” it because the standard answer to the proof of heliocentrism is through high precision measurements of stellar parallax. And it was only in 1838 that stellar parallax was first measured.
Using a heliometer designed by German physicist Joseph von Fraunhofer, German astronomer Friedrich Wilhelm Bessel was the first to measure stellar parallax in 1838. Choosing 61 Cygni, a star barely visible to the naked eye and known to possess a relatively high velocity in the plane of the sky, Bessel showed in 1838 that, after correcting for velocity, the star apparently moved in an ellipse every year. This back-and-forth motion was the annual parallax. Astronomers had known for centuries that such an effect must occur, but Bessel was the first to demonstrate it accurately.
No one in Galileo’s time or for 150 years after his death was able to demonstrate this necessary effect of earth’s motion around the sun. Stellar parallax was finally observed in 1838 by Friedrich Bessel, a German scientist. But it is not Bessel that is credited with finally proving that the earth moved around the earth. In 1729, James Bradley, while searching for the elusive stellar parallax, detected motion of the stars over the course of the year which did not fit the pattern of stellar parallax. He had discovered stellar aberration, which is also related to the motion of the earth. Regardless, proof of the earth’s motion was not available in the seventeenth century and those arguing for it’s motion had no answer for why stellar parallax could not be observed. It is a huge problem when a consequence of a theory is expected and it cannot be observed. It is enough to keep a hypothesis from being accepted as a proven theory, regardless of the number of positive arguments in its favor.
Even Brahe knew about stellar parallax. And it was because of his measurements and no observance of stellar parallax that he based his model on geocentrism rather than heliocentrism.
He made the best measurements that had yet been made in the search for stellar parallax. Upon finding no parallax for the stars, he (correctly) concluded that either:
– the earth was motionless at the center of the Universe, or
– the stars were so far away that their parallax was too small to measure.
Not for the only time in human thought, a great thinker formulated a pivotal question correctly, but then made the wrong choice of possible answers: Brahe did not believe that the stars could possibly be so far away and so concluded that the Earth was the center of the Universe and that Copernicus was wrong.
The geocentric model is no more crazy than saying that a tennis ball is made of protons, neutrons and electrons. Sure, we all (most of us) believe there are these particles like electrons – but how do normal humans know this? In fact, the evidence in our everyday lives doesn’t make it obvious that there are protons and electrons (yes, you could argue the mere fact of things like computers says these have to exist). The same is true for the heliocentric model.
Find a human that has never looked at a science book and doesn’t know anything about the solar system. Now ask this human if the Earth moves around the Sun or the Sun moves around the Earth. I would bet most of these isolated humans would pick the geocentric model. It just doesn’t feel like the Earth is moving.
There is another very convincing argument for the geocentric model – stellar parallax (or lack of).
The ancient Greeks claimed that if the Earth is moving around the Sun then the stars should shift their positions due to this orbital motion (called stellar parallax). Guess what? The stars don’t shift. Well, they don’t shift enough for you to notice, but they do indeed shift. This is essentially the same reason the moon appears to follow you around when you drive – it’s too far away for any apparent shift due to your motion.
So, to answer my question, to prove heliocentrism is true would require observing stellar parallax. The ancient scholars knew this, but they did not detect it. So, geocentrism was commonly accepted for almost two millennia because that is what the observational evidence supported. And it was only in 1838 that heliocentrism was proven to be true. Before then, there was no proof, only evidence to suggest it could be true.
Now, it’s doubtful the regular ancient people knew about stellar parallax. Even most modern people don’t know about it. Observationally it appears the heavenly bodies orbit around us. There is no reason to think otherwise, even for those whose profession was to observe the stars. So, it is chronological snobbery to look down on people in the past for accepting geocentrism.