I saw a list recently of the moons of the various planets and the discoverer(s) and date of discovery. Earth's Moon was listed as Unknown.

I know you don't 'discover' a huge disc in the sky. But still, what is the first recorded reference to the Moon being a satellite of the Earth? That someone knew it is smaller and orbiting? Celestial Sphere does not count.

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    $\begingroup$ The moon's orbital period was probably the second thing that ancient farmers figured out. The sun being the first. Babylonians had discovered the lunar saros by 1000 BC. As far as who had the original idea that Earth was the center of the Earth/Moon system - it came during the middle ages when the moon was accepted as a sphere. Galileo figured out moons orbit parent bodies, and Newton developed laws of motion and celestial mechanics. It wasn't one single person... $\endgroup$ – EastOfJupiter May 4 '16 at 12:58
  • $\begingroup$ @EastOfJupiter Long before that we had Aristotle that proposed that the moon (and 54 other things) orbited the earth. Or, more precisely, that there are 55 crystalline spheres surrounding the earth that everything was attached to, and the moon was on #1. I'm not sure why the OP wants to specifically exclude this. $\endgroup$ – zibadawa timmy May 4 '16 at 13:17
  • $\begingroup$ Otherwise I would expect that for western cultures the discovery of Jovian satellites is a good approximation for this date. But for eastern societies? Not so sure. Mythologies can be pretty poetic and heavily subject to interpretations and translations. Chinese mythologies apparently have a story about the moon which mentions the sun (and it's 9 now-murdered siblings) circling the Earth, so hypothetically the Chinese of ~2170 b.c. considered the moon a satellite, by some vaguely modern definition of "satellite". $\endgroup$ – zibadawa timmy May 4 '16 at 13:33
  • $\begingroup$ Thank you for the edits and comments. I was trying to make the question somewhat surprising and amusing, in the sense that we do not always think of obvious things... To me, a celestial sphere is not a satellite, it misses the point of seeing the moon as a round body in space like the earth (differing shadow lengths on different locations at once confirm that Earth is a ball: ancient Greeks). So, I guess the prize goes to the Chinese in 2170 b.c., for making a recognizable statement that aligns with the facts. We can now amend our store of knowledge. $\endgroup$ – user11722 May 4 '16 at 13:51
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    $\begingroup$ I think it's an interesting question - the folks over in History of Science and Math Stackexchange do en excellent job. I think a question along the lines of "What is the first recorded evidence that the moon was understood to be, or at least though to be a satellite orbiting the earth?" might be well received. You could specify if want to know if it was thought to be gravitationally bound to the earth, or just circling the earth for unknown reasons. Of course if you don't specify, you might get both answers! Check to see if it's already been answered. $\endgroup$ – uhoh May 5 '16 at 5:06

From before the dawn of history people naturally assumed that the sky was a solid dome above the flat earth. The dome was assumed to rotate once a day, so the stars were assumed to be lights attached to the dome.

Anyone who assumed that the sky dome was opaque had to assume that the sun and the wandering planets were nearer than the sky dome. I think that it was usually assumed the sky dome was opaque and colored blue, thus making the sky seem blue when it reflected the light of the sun during the day, thus making the sun closer than the sky dome.

Those who kept records of astronomical observations soon noticed that the moon occulted or passed in front of stars, planets, and the sun (solar eclipses), and thus was closer.

Everyone assumed that the sun and the moon were tiny, until traveler's reports showed that they had the same apparent diameters every place that as visited, and so were about equally far away from every place that was visited. Thus as the size of the known world grew larger and larger, the minimum possible size and distance of the moon and the sun grew larger and larger.

The idea of a spherical earth was proposed and gradually accepted by Greek philosophers between the sixth and third centuries BC. Thus the earth became known as Earth, a sphere instead of a flat disc, and the dome of the sky became a hollow spherical shell around it.

In Hellenistic times the diameter of the Earth was calculated with reasonable accuracy, as well as the distance to the moon and thus its diameter. So it became known that the moon was about a quarter the diameter of the Earth and over sixty Earth radii distant.

Because of solar eclipses, it had been known since prehistoric times that the moon was closer than the sun, and keepers of astronomical records of events when the moon occulted (passed in front of) stars and planets knew that the moon was closer than planets and stars.

Anyone who assumed geocentrism, that the Earth was the enter of the universe, naturally assumed that every object revolved around the Earth, including the moon, and that the moon was thus the closest satellite of the Earth. A few ancient Greek philosphers supported the Heliocentric theory, that the Earth and the planets revolved around the sun. Some of them could have believed that the moon also revolved around the sun, but as far as I know all heliocentric believers also had the moon revolve around the Earth.

By the last few centuries BC there were many educated persons who believed that the Earth, the moon, and the sun were giant balls of rock (and thus somewhat similar objects), that the sun was a giant burning rock, and that the stars and planets might also be giant burning rocks far, far away from the Earth and appearing as dots as seen from Earth. Since everybody already since prehistoric times believed that the moon revolved around the Earth, by the last few centuries BC educated people in Western civilization believed that the moon was what we now call a natural satellite of the Earth, though some of them believed and some did not that the sun and planets were also natural satellites of the Earth.

  • $\begingroup$ Very nicely written, and probably the best answer I am likely to get. I just keep wondering why, when all this was pretty well known so long ago, that it took so long to be accepted and why 1500 years later people were still being burned at the stake for having what amounts to common sense? But I guess that is a question for Religion.SE. $\endgroup$ – user11722 May 29 '16 at 17:55
  • $\begingroup$ Not a criticism, but I've always felt the flat Earth assumption was overstated. The curvature of the Earth is visible if people get the right point of view, even in antiquity and the "on the back of a turtle", seemed to me to be a statement of the recognition of Earth's shape, as much as it is a believe in giant turtles. A fable built on a real observation, which doesn't change your answer, but I wanted to put that out there. $\endgroup$ – userLTK Jul 19 '19 at 2:27
  • $\begingroup$ @User11722 Common sense is a dangerous term to use in the history of science. Today, we have the benefit of evidence that they didn't have in the 16th century. I asked a related question here, and you might enjoy some of the answers. It wasn't clear, based on the evidence that geocentrism was wrong. The geocentric model worked. It made accurate predictions. hsm.stackexchange.com/questions/1979/… $\endgroup$ – userLTK Jul 19 '19 at 2:41

I believe the earliest known depiciton of the Moon is that on the 'Nebra Sky Disc' which is said to be 4000 years old. Also, it could be (but not confirmed) depicted on the Tal-Quadi slab which is dated over 5000 years old.

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    $\begingroup$ but how are these "recorded reference(s) to the Moon being a satellite of the Earth" specifically. Did they somehow convey that the Moon is a body in space orbiting the Earth? $\endgroup$ – uhoh Jul 19 '19 at 4:17
  • $\begingroup$ References, please. $\endgroup$ – Jan Doggen Jul 19 '19 at 13:04
  • $\begingroup$ They are documented by the most primitive means of the time. How else would they be documented 4000-5000 years ago? $\endgroup$ – insum snoy Jul 20 '19 at 10:19

In the geocentric system, the Moon is still, in a sense, a satalite of the Earth, as is the sun, the planets and the stars as they all orbit the Earth. Aristotle is often credited for the geocetric model, but there are writings that preceed him that describe it. The idea that the Moon orbits the Earth may be even older than that, but I couldn't find anything on that.

I think one of the interesting things the ancient Greeks came up with, was they may have been the first society for whom the Moon was no longer a god. Their gods were human like, not the Sun, the Moon, Nature, etc. The Sun and Moon became objects in the sky instead of part of their mythology. But I digress.

The first written and worked out calculation that the Moon was smaller than the Earth and orbited the Earth as a "moon", and that the Earth was smaller than the Sun and orbited the Sun came from Aristarchus of Samos, who came not long after Aristotle in the 3rd century BC.

If Aristarchus had been a few years earlier, perhaps his analysis would have swayed Aristotle, but that's just speculation on my part. Aristotle's ideas came first and he was well respected and well read.

Ptolomy of Alexandria who'd writings follow about 3 centuries later, knew of both Aristotle's and Aristarchus' models, but he found Aristarchus' model troubling because he thought that the Earth's rotation speed would create high speed winds not seen on Earth, so he leaned towards Aristotle's model and, in addition to that, using epicycles, the Ptolemaic model was highly predictable. It explained planetary motion and people like that.

Predictions, a model that fits what we see as well as the respect for Aristotle's teachings and the Church saying "this is so" may have all played a role in the 15 centuries that the Ptolemaic model endured. We shouldn't judge that as stupid, because there was a logic to it and a lack of evidence to say otherwise. If a system works and can't be shown to be false, it's likely to stick around.

There may have been the occasional scholar who read Aristarchus during the middle ages and agreed with him, and I've read that Copernicus credits Aristarchus, but that wouldn't be enough to sway the accepted theory. Tycho Brahe, for example, who came after Copernicus but preceded and later coincided with Galileo, went back to a revised geocentric model. See Tychonic system where the Moon, Sun and Stars orbit the Earth.

Galileo's telescope, however, provided proof to the contrary of the Ptolemaic system. He discovered Jupiter's 4 large moons, later named the Galilean moons and he observed the phases of Venus and later, he timed the tides to the Moon's and Sun's orbit. Galileo was the first to provide proof that the Moon was a satellite of Earth and that other planets could have moons.


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