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B Aristotle and geocentric

  1. Apr 26, 2017 #1
    I'm interested to find out why he went with Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn as his order (in fact on one wiki page it has Sun as 2nd though this seems wrong). However the moon being so prominent in the sky and sun also followed by mercury and Venus as inner planets always observed relatively close into the sun would have seemed a reasonable assumption to him?

    I've tried to search but can't find out why?

  2. jcsd
  3. Apr 26, 2017 #2

    After having a quick read through of his description of the geocentric model, the only reasonable conclusion that I would come to would be that he interpreted that particular order being the order of distance from the Earth.

    ie, the moon closest to Earth then the Sun, then Mercury, then Venus, then Mars etc..

    It's obvious to us now that this isn't the case, but perhaps it wasn't obvious to Aristotle when observing these bodies.

    For example, Aristotle not knowing that the planets are orbitting the Sun, and observing another planet in the solar system could lead him to misinterpret the distance to said planet.

    This is my interpretation anyhow.

    Hope it helps.
  4. Apr 26, 2017 #3
    Hiya, yes that's why I said that would make sense but his actual suggested order was moon, mercury, Venus Sun etc. I can't see why he's put sun at 4th?
  5. Apr 26, 2017 #4
    Well I suppose he could have misjudged the size of the planets and sun. But where have you read he placed the sun fourth if you don't mind me asking?
  6. Apr 26, 2017 #5
    upload_2017-4-26_22-28-5.png Hi again, there are a number of pictures like this.
    upload_2017-4-26_22-31-16.png I think it may have been that the moon (luna), mercury and venus were all observed, at some point, passing infront of the sun so must be on an inner celestial sphere?
  7. Apr 26, 2017 #6


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    This is just an informed guess.
    Of all the bodies the Sun wanders the least in the sky. As such it seems in its own category. To make the model aesthetically pleasing you could either put it at the front in the back, or in-between some other two groups.
    It can't be at the front, since solar eclipses are a thing (hence Moon is first).
    Not at the back because... beats me. Unless the ancient Greeks could verify whether a planet can or cannot transit. (could they?)
    But as a demarcation between two other groups, it works fine with the inner and outer planets (as we know them today). The inner ones wander less than the outer ones (and differently - no apparent retrograde motion), hence two nice groups of wanderers (gr. planetes) and the stately sun in-between.
    Why the order of planets in each group such as it is - this again eludes me. It could be another aesthetic argument about how much of wandering a planet should do.
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