What is the first recorded reference to the Moon being a satellite of the Earth?

  • 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.


    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...

    @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.

    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".

    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.

    @zibadawatimmy - I excluded the spheres proposed by Aristotle because the OP specifically asked that celestial spheres not be considered an appropriate explanation of the moons' motion through our skies.

    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.

    If what you want is "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)", then I think the answer would have to be classical Greece (e.g., 5th or 4th C BC). Lots of mythologies have both the Sun and the Moon going "around" the Earth, but with the Earth as e.g. a disk. This probably applies to the Chinese case, since Chinese science never conceived of the Earth as a "ball" (and the "2170 BC" date for that folk tale is pure fantasy).

    @PeterErwin OK, well, maybe there is not a hard answer, but the question is valid as a way of considering when we learn facts and how amazingly long it takes for them to be accepted!

    While his method was off for the Moon and accuracy off for the sun, Aristarchus of Samos was the first person to somewhat accurately measure and figure out that the Moon was smaller than the Earth and the Sun, quite a bit larger. http://www.astro.cornell.edu/academics/courses/astro201/aristarchus.htm He came after Aristotle, so Aristotle had no way of knowing about his work, which is too bad because if he had, he might have liked it and the history of science might have avoided the whole geocentric argument that lasted for nearly 2,000 years.

    @userLTK Right, but then we would have gotten stuck on Aristarchus' ideas instead. It is just that we would be arguing about them while living on the moon and Mars by now. Which is my point. The Catholics could be on New Ireland, and the Protestants on NewNew Ireland, and they would be too far apart to throw bombs at each other while arguing about which star God lives on.

    @nocomprende Not to turn this away from the subject at hand, but I agree. History is very good at repeating itself.

  • 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.


    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.

    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.

    @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. https://hsm.stackexchange.com/questions/1979/why-didnt-aristarchus-theory-of-heliocentrism-stick

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Content dated before 7/24/2021 11:53 AM