How did they figure out that Earth revolved around the Sun so long ago without benefit of our modern science?

Answer 1

In addition to what MataHari said, and in term of the Greeks and pre-Renaissance thought, there was one other hint that the Earth might be going around the Sun instead of vice versa. This is that the planets, if you watch their motion against the background of stars over several months and years don't move through the constellations in the same direction all the time. Sometimes they appear to slow down, stop, move backwards, stop, and then continue moving in the direction they were originally moving. This kind of motion is called retrograde motion, and it happens when one planet laps another while orbiting the Sun (see the Wikipedia article I've put as a source, it has a nice diagram).

Now, this is not doom to the geocentrists. Indeed, many geocentrist astronomers spent a lot of time to explain this effect, and to some extent they succeeded. But the result was that their explanation of the structure of the Solar System became much more complicated, while for a heliocentric model, there was no need for extra complications to explain this motion. Thus, in some sense, the heliocentric explanation was more "elegant". You might think that this is unimportant, but Aristotle and his gang had astronomers convinced that all orbits had to be circular until the beginning of the 17th century, because circles were the "perfect" and "most elegant" shape. It wasn't until Kepler (which was some time after Copernicus) that this idea was finally done away with. So, ideas which are seen as more "elegant" sometimes can hold sway over less elegant ones, for better or for worse.

I should note again, that this wasn't a clinching fact, but it was a hint.

As to how pre-20th century astronomers figured it out, basically the clinching observation there was Galileo's observations that Venus had phases like the Moon, and the only way this could be accounted for was if Venus was going around the Sun and not the Earth. Moreover, with Kepler's Laws, the heliocentrists had a model of the solar system which was much more accurate, precise, and simple than any geocentric model. And when Newton came up with his Law of Universal Gravitation, and was able to show that Kepler's Laws were a natural result of gravity, that kind of clinched it. Not only did we know how the planets were moving to high precision, we knew *why*.

Answer 2

The first actual proof (1725) was that telescopes had to be tilted in the direction of Earth's movement because the speed of light was not infinite. The tilt of the telescope is like tilting an umbrella forward when you are running under the rain.
See link below on aberration of light.

The angle is not much, but it was measurable. It would not have been measurable before the invention of the telescope.

However, even as far back as Greeks, when they tried to explain the way planets (including the Sun and the Moon) moved, they tried various combinations and, for some combinations to work (meaning: to make predictions that were close to the actual observations), some models required the Earth to be moving (but not always around the Sun!). Most models were complicated and had problems i.e., some contradictions with actual observations -- for example, in the early earth-centred models, Venus should have always be at the same distance from Earth, but its changes in brightness were easy to see and could not be explained.

The first model that made good predictions AND was simple is Kepler's. Planets on ellipses with the Sun at one focus. Earth became one of the planets.

Up to then, most models would only use 'perfect' circles; that is why they did not work very well, even when Copernicus put the Sun at the centre. His system was not much better than the others for predicting the position of planets (and it was just as complicated, with deferents and epicycles and such).

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Although religion did cause problems at the time of Galileo, the early rejections of Sun-centred models had nothing to do with religion, they had to do with observations.

For example, it was thought that the universe was relatively small (the stars were all fixed on a sphere). If the Earth orbited around the Sun (and the Sun was known to be quite far), then we should be closer to one side of the celestial sphere than the other side. As we change position around the Sun, then some constellations should appear larger in Winter than in Spring or Summer. That is not the case, therefore we are not moving.

Today we know that the stars are far, very far away compared to Earth's orbit -- but they did not know that (they could not even imagine such 'astronomical' sizes)

Answer 3

Some of the Greek philosophers did work it out. It is not difficult once you get over the fact that the Earth is not the centre of things.

The problem has always been religious fanaticism. People were told that the universe was created perfectly by God with earth at the centre. Many enlightened people were tortured or executed for arguing otherwise. Even Galileo was forced by the Catholic inquisition to denounce the notion that the sun was the centre of things. he was offered denounce or torture - what would you do.

Go see if you can get the DVD Galileo. That will show you how religion has stifled science.

I believe that sailors thousands of years ago would have known the Earth was round. Every time they approached an island they would see it come up over the horizon, bit by bit. Doesn't take a lot of working out, does it.

But who would listen to a sailor?

Answer 4

Basically around 270 BC, Aristarchus, using trigonometry, used the position of the half-full moon to estimate the distance to the sun. Based on his calculations about the distance to the sun, he was able to determine that the sun was actually much larger than the Earth, (based on the size in the sky relative to the distance) and concluded that because it was so much larger, it was more likely that the Earth orbited the sun rather than vice versa.

This theory was later posed by Copernicus and proven by Gallileo's observation of the phases of Venus.

Answer 5

The solar (Sol) and the Earth are a factor of the photograph voltaic gadget. The photograph voltaic gadget is a factor of the Milky way Galaxy. The photograph voltaic gadget orbits the centre of the galaxy so subsequently Sol does one orbit or spin around the Earth each 250 Million three hundred and sixty 5 days approx.

Answer 6

Copernicus wrote a book, "On the Revolutions of Heavenly Spheres". It shows that geometry supported a more static Sun and a motion-inclined Earth.

If you would like to read it, look into:

"On the Shoulders of Giants" by Stephen Hawking.

Answer 7

The baleful influence of Ptolemy writing in the 2nd Century AD set back Western thinking on this subject for 1400 years but there were a variety of dissenting voices who were proponents of heliocentrism that we tend not to hear about ...

Answer 8

Astronomers did the math, and figured out something was wrong with the current beliefs. And they also studied the stars and planets so much, they figured out it can't be the was Aristotle thought it was.