Heliocentrism: Definition, origin and model

In geocentric teaching, the Earth was considered immovable. Distances in geocentric astronomy were much smaller than the modern, heliocentric solar system distances too. Example, the distance to Mars was not worked out until 1672 when the Mars parallax was measured using telescopes. Giovanni Cassini Biography, https://www.space.com/18902-giovanni-cassini.html

The distance to the stars using Claudius Ptolemy system and Tycho Brahe were only about 0.85 AU from Earth using the modern AU measurement where 1.0 is the value today. Claudius Ptolemy considered the distance of the sphere of fixed stars was 20,000 earth radii. Using 6378 km, the sphere of fixed stars was 1.2756E+8 km distance from earth. That is about 0.85 au using today's distance for the astronomical unit. The solar system and universe of the spheres used by Claudius Ptolemy was much smaller than modern astronomy measurements.

The Depth of the Heavens -- Belief and Knowledge during 2500 Years, https://ui.adsabs.harvard.edu/abs/2003BaltA..12..451H/abstract
 
  • Like
Reactions: Helio
I have about 2 cents of stuff to add.... :)

However, Nicolaus Copernicus wasn't the first person to suggest this. As early as a thousand years before that, the 5th century Greek philosophers Philolaus and Hicetas suggested that the Earth could be circling a fiery object, according to the American Philological Association(opens in new tab). Greek astronomer Aristarchus of Samos suggested that this object was the sun two centuries later.
Yes, and Copernicus used some if not all these names in his publication to give his model more credibility. Copernicus was one of the first to translate Greek into his Polish language, IIRC.

Because nobody was able to explain why the stars looked the same despite Earth changing position, the geocentric model became more widely recognised.
The Geocentric model came more from Aristotle arguing that heavier materials move to take their natural position, namely toward the center of the Earth. Rocks would fall downward through air and water, water downward from air, etc. This would obviously produce a spherical object as Aristotle made clear, as well as, Earth being the center of the “world” as they called our universe, even into the times of Galileo.

The lack of motion of the stars relative to a proposed moving Earth was the main argument against Copernicus. Many were convinced that the brighter stars appeared larger, thus if they were really, really far away then they would have to be really, really large, far larger than the Sun. This was not credible.

Egyptian astronomer and mathematician Claudius Ptolemy overcame this problem with a new theory, that the Earth was fixed at the center of the solar system.
I suspect this could be rephrased with Ptolemy having presented an improved model over Aristotle’s. Ptolemy’s goal wasn’t as much to offer a new physics theory but simply to have a way to more accurately predict planetary positions for the important astrological uses, including medicine. Ptolemy introduced his equant which had the effect of making the orbits closer to what they really are even though he, like Copernicus, were convinced perfect circles defined the orbits.

By answering the question of what was at the center of the solar system, astronomers were able to find the answers to other questions, too. Mercury and Venus' orbits were placed between the sun and Earth, which revealed to astronomers why they appeared so different in size and shape over time, according to Universe Today(opens in new tab).
Both models, however, did this. The appearance difference didn’t become much of an issue until Galileo applied his telescope to the phases of Venus, which proved the geocentric model as false. So, the Tychonic model became the preferred model over the Heliocentric, at least by the Church, which had the top universities and scientists.
When the planets were on the far side of the sun relative to the position of Earth, these planets were much smaller in the sky. When on one side of the sun, the light hitting the planets gave them a crescent shape.
Yes, but the brightness didn’t change that much since the crescent phase has only a portion of the disk with illumination but over a larger area, where the gibbous phase had more area of illumination but was smaller in apparent size due to the greater distance.

According to NASA, Kepler and Newton worked out precise measurements of the planets' movements around the sun, while Galileo used his telescope to prove heliocentrism.
Galileo was able to falsify the Geocentric model, but could never prove heliocentrism. His best argument, in his view, was how tides worked, which was very clever but erroneous. This is part of the story why he was forced into house arrest at an old age.

Proofs are in mathematics. A physics theory can never be proven since some future falsification would invalidate it. The Geocentric model, which lasted for over 2000 years, is a good example of this.
 
Last edited:
  • Like
Reactions: rod
Something that is not commonly reported about the geocentric astronomy today. The flat earth folks hold rigorously to the immovable Earth and geocentric solar system today (perhaps other groups too). Here is an example from the Flat Earth Society on stellar parallax.

Stellar Parallax - The Flat Earth Wiki (tfes.org)

According to this report, stars that show negative parallax measurements do not support the heliocentric solar system, about 25% of a catalog they used showing some 1 million targets or more. However, they do not offer much to explain the other 75% where positive stellar parallax measurements are found other than the some stars moving around the Earth or the Earth moves relative to some stars.

"Conclusion It is an indisputable fact that stellar parallax, like the phases of Venus, has been widely cited as 'proof' that the World orbits the Sun. This is unfortunate, since the phenomenon proves no such thing. The only thing it does prove is that either the World is moving with respect to the stars, or that the stars are moving with respect to the World."

Something I note here about the wiki argument. Not only do we see stellar parallax changes for the majority of stars observed where such measurements can be made (out to perhaps about 7,000 to 8,000 ly distance), we also see the Sun's angular diameter changes in the course of the year too that show up nicely at perihelion and aphelion distances as Earth moves around the Sun in a slightly elliptical shape orbit. Just a reminder here, we do have geocentric astronomy teachers today in some groups.

Update on this post. Stellar parallax of 7 mas indicates the star is about 466 LY from Earth or almost 143 pc. Stellar parallax of 1 mas is 1kpc distance or almost 3300 LY from Earth. There are limits to measuring positive stellar parallax with such tiny angular size changes. The star 61 Cygni parallax is about 314 mas so close to 10.4 LY from Earth, the first stellar parallax measured in 1838.
 
Last edited:
  • Like
Reactions: Helio
Something that is not commonly reported about the geocentric astronomy today. The flat earth folks hold rigorously to the immovable Earth and geocentric solar system today (perhaps other groups too). Here is an example from the Flat Earth Society on stellar parallax.

Stellar Parallax - The Flat Earth Wiki (tfes.org)

According to this report, stars that show negative parallax measurements do not support the heliocentric solar system, about 25% of a catalog they used showing some 1 million targets or more. However, they do not offer much to explain the other 75% where positive stellar parallax measurements are found other than the some stars moving around the Earth or the Earth moves relative to some stars.
Negative parallax comes when the background “fixed” stars exhibit motion. This is why the far more distant quasars are used. I strongly doubt they have any parallax countering Earth’s motion.

"Conclusion It is an indisputable fact that stellar parallax, like the phases of Venus, has been widely cited as 'proof' that the World orbits the Sun. This is unfortunate, since the phenomenon proves no such thing. The only thing it does prove is that either the World is moving with respect to the stars, or that the stars are moving with respect to the World."
It was the lack of stellar parallax that made the heliocentric model unacceptable, though it was powerful in unification and elegance. If one could imagine the vast distances to stars, then it was fine. It was extra hard in that time because folks assumed God wouldn’t want to “waste all that empty space.” Ptolemy placed Venus between Earth and Sun for this very reason. Teleology was very popular.

But they are correct that the appearances could be made to be the same if one thinks the entire universe rotates and wiggles rather than the ultra tiny Earth. The modified Tychonic model has never been falsified, but it did become more silly with greater discoveries.

Eliminating the one big argument against the heliocentric model (no stellar parallax) of course made the theory quite strong. It was never a proof, however.

Something I note here about the wiki argument. Not only do we see stellar parallax changes for the majority of stars observed where such measurements can be made (out to perhaps about 7,000 to 8,000 ly distance), we also see the Sun's angular diameter changes in the course of the year too that show up nicely at perihelion and aphelion distances as Earth moves around the Sun in a slightly elliptical shape orbit. Just a reminder here, we do have geocentric astronomy teachers today in some groups.
Yes, but in a mod. Tychonic model, this would be the case as well. :)


Update on this post. Stellar parallax of 7 mas indicates the star is about 466 LY from Earth or almost 143 pc. Stellar parallax of 1 mas is 1kpc distance or almost 3300 LY from Earth. There are limits to measuring positive stellar parallax with such tiny angular size changes. The star 61 Cygni parallax is about 314 mas so close to 10.4 LY from Earth, the first stellar parallax measured in 1838.
Yes, almost 300 years of technology was needed. Stellar aberration came much earlier serendipitously.
 
  • Like
Reactions: rod
Negative parallax comes when the background “fixed” stars exhibit motion. This is why the far more distant quasars are used. I strongly doubt they have any parallax countering Earth’s motion.


It was the lack of stellar parallax that made the heliocentric model unacceptable, though it was powerful in unification and elegance. If one could imagine the vast distances to stars, then it was fine. It was extra hard in that time because folks assumed God wouldn’t want to “waste all that empty space.” Ptolemy placed Venus between Earth and Sun for this very reason. Teleology was very popular.

But they are correct that the appearances could be made to be the same if one thinks the entire universe rotates and wiggles rather than the ultra tiny Earth. The modified Tychonic model has never been falsified, but it did become more silly with greater discoveries.

Eliminating the one big argument against the heliocentric model (no stellar parallax) of course made the theory quite strong. It was never a proof, however.

Yes, but in a mod. Tychonic model, this would be the case as well. :)


Yes, almost 300 years of technology was needed. Stellar aberration came much earlier serendipitously.
Helio said, "Negative parallax comes when the background “fixed” stars exhibit motion. This is why the far more distant quasars are used. I strongly doubt they have any parallax countering Earth’s motion."

My opinion, negative stellar parallax measurements found I feel need more study and explanation especially in forums discussions or popular science reporting sites. I first encountered this argument from flat earth folks back in 2016. Here are some examples of negative stellar parallax reported.

Machine Learning Classification of Gaia Data Release 2, https://arxiv.org/abs/1808.05728, "...For the objects with negative parallaxes, about 2.5\% are galaxies and QSOs, while about 99.9% are stars if the relative parallax uncertainties are smaller than 0.2..."

KIC 2568888: To be or not to be a binary, https://arxiv.org/abs/1810.06206, "...From Gaia we obtained for one object a distance between and broadly consistent with the distances from BVI photometry. For the other object we have a negative parallax with a not yet reliable Gaia distance solution. The derived distances challenge a binary interpretation and may either point to a triple system, which could explain the visible magnitudes, or, to a rare chance alignment (∼0.05% chance based on stellar magnitudes). This probability would even be smaller, if calculated for close pairs of stars with a mass ratio close to unity in addition to similar magnitudes, which may indeed indicate that a binary scenario is more favourable."

Validation of the new Hipparcos reduction, https://arxiv.org/abs/0708.1752, "...The internal errors are followed through the reduction process, and the external errors are investigated on the basis of a comparison with radio observations of a small selection of stars, and the distribution of negative parallaxes. Error correlation levels are investigated and the reduction by more than a factor 10 as obtained in the new catalogue is explained. Results.The formal errors on the parallaxes for the new catalogue are confirmed. The presence of a small amount of additional noise, though unlikely, cannot be ruled out."

Negative stellar parallaxes reported are used to argue against the heliocentric solar system by some today.
 
  • Like
Reactions: Helio
Negative stellar parallaxes reported are used to argue against the heliocentric solar system by some today.
I suspect a Geocentric model would also struggle with pos. and neg . parallax measurements. Motions are relative. The credibility difference between the models is the issue. Hyper motions of the cosmos, including wobble about the orbiting Sun, requires incredible fictions forces for causation.
 
  • Like
Reactions: rod

ASK THE COMMUNITY