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In Pre-Copernican Time, Did the Sun Circle the Earth Once Each Day or Once Each Year?

  1. Dec 4, 2011 #1
    In the time before Copernicus introduced the idea that the planets including the Earth orbit the Sun, how were the daily and annual cycles reconciled?

    I have always assumed that in the Copernican view the Earth orbits the Sun once each year. But not till today did I wonder about the 24-hour daily cycle: In pre-Copernican time, the Earth must have been seen as rotating once each day. That is, the Earth might have been seen as the center of the universe, but it must have been seen as rotating every day even if it was considered otherwise stationary in space.

    If the Sun was regarded as circling the Earth ONCE EACH DAY, then how were the annual cycles explained? Just wondering if anyone has any insight into this.
    Last edited by a moderator: Dec 4, 2011
  2. jcsd
  3. Dec 4, 2011 #2
    Re: In Pre-Copernican Time, Did the Sun Circle the Earth Once Each Day or Once Each Y

    Various people thought various things. But most DID deny
    that the earth rotated. They thought that the atmosphere
    would not go round with the solid earth, and so there would
    be perpetual high winds. Of course, the existence of the Coriolis
    effect shows there is a bit of truth in that.

    Annual changes had then to be accounted for by various ad hoc
    theories such as that of the celestial spheres doing complicated

    One has to remember that people knew nothing of distant bodies'
    natures. One thory was that the sun was a hole in a rotating crystal
    sphere, through which the external fires showed - really not a thing at
    all, but more like a moving window.
  4. Dec 4, 2011 #3


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    Re: In Pre-Copernican Time, Did the Sun Circle the Earth Once Each Day or Once Each Y

    Middling is right that various models were proposed. FWIW here is a paragraph from Wkpd that illustrates the diversity of opinion:
    Not all Greeks agreed with the geocentric model. The Pythagorean system has already been mentioned; some Pythagoreans believed the Earth to be one of several planets going around a central fire.[19] Hicetas and Ecphantus, two Pythagoreans of the 5th century BC, and Heraclides Ponticus in the 4th century BC, believed that the Earth rotated on its axis but remained at the center of the universe.[20] Such a system still qualifies as geocentric. It was revived in the Middle Ages by Jean Buridan. Heraclides Ponticus was once thought to have proposed that both Venus and Mercury went around the Sun rather than the Earth, but this is no longer accepted.[21] Martianus Capella definitely put Mercury and Venus in orbit around the Sun.[22] Aristarchus of Samos was the most radical. He wrote a work, which has not survived, on heliocentrism, saying that the Sun was at the center of the universe, while the Earth and other planets revolved around it.[23] His theory was not popular, and he had one named follower, Seleucus of Seleucia.[24]

    You might be interested by what Wkpd says about Aristarchus (born 310 BC). He had a fullyworked heliocentric system with the sun stationary and the sphere of fixed stars stationary. He had the known planets in the correct order of distance from the sun. And of course the earth rotated.
    This quotes a book by Archimedes, which has survived and which describes Aristarchus' system.

    I think the answer is that most people did NOT think of the earth as rotating daily, but curiously enough some people did have that idea going back to before the 3rd century BC.

    Your other question about how they handled the season variation in the course of the sun is discussed some in that "heliocentrism" article. For example Anaximander imagined a large ring or wheel rotating in the east-west plane around the earth which could SHIFT northwards in summer and southwards in winter. Like a hula-hoop which a person makes rise and fall while spinning. The article shows a picture of his system with its two wheels, one for sun and one for moon, with the sun wheel in both the summer and winter configurations.
    Last edited: Dec 4, 2011
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