equant

• “Nor should we attribute Copernicus's desire for uniform circular motions to an aesthetic need, for this idea was philosophical not aesthetic, and Copernicus's replacing the equant with epicyclets made his system more complex than Ptolemy's.”

  Nicolaus Copernicus

• “Surprisingly, given that the elimination of the equant was so important in the”

  Nicolaus Copernicus

• “Reinhold did not accept the heliocentric theory, but he admired the elimination of the equant.”

  Nicolaus Copernicus

• “Disturbed by the failure of Ptolemy's geocentric model of the universe to follow Aristotle's requirement for the uniform circular motion of all celestial bodies and determined to eliminate Ptolemy's equant, an imaginary point around which the bodies seemed to follow that requirement, Copernicus decided that he could achieve his goal only through a heliocentric model.”

  Nicolaus Copernicus

• “What appealed to them in Copernicus™ model was its ability to do away with ad hoc devices in Ptolemy's system (such as the equant), to explain key phenomena in a pleasing fashion (the observed retrograde motion of the planets), and to explain away otherwise inexplicable coincidences in Ptolemy's system (such as the alignment of the Sun and the centres of the epicycles of the inferior planets).”

  Thomas Kuhn

• “On the apse-line at a distance from the deferent's center equal and opposite to the earth's, Ptolemy placed an equant.”

  Dictionary of the History of Ideas

• “At the same time in the Islamic world Ibn al-Shatir of Damascus rejected Ptolemy's equant as a violation of the principle that a cosmic body's orbit must be compounded from absolutely uniform circular motions.”

  Dictionary of the History of Ideas

• “To this Tycho objected, and Kepler had great difficulty in convincing him that the new move would be any improvement, but undertook to prove to him by actual examples that a false position of the orbit could by adjusting the equant be made to fit the longitudes within five minutes of arc, while giving quite erroneous values of the latitudes and second inequalities.”

  Kepler

• “Their aim was to find a position of the “equant,” such that these observations would show a constant angular motion about it; and that the computed positions would agree in latitude and longitude with the actual observed positions.”

  Kepler

• “[Footnote 4: I.e. the angular motion about the equant was uniform.]”

  Kepler

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