The Dance Of Copernicus

The Dance Of Copernicus


During the last few days of May, guests at Primland were treated to a great spectacle- the conjunction of three planets in the western sky- Mercury, Venus, and Jupiter. Ironically, the peak of thsi conjunction occured just after the anniversary of one of the greatest astronomers of all time, Nicolas Copernicus. In a sense, this conjunction is a fitting tribute to Copernicus, who helped us understand their proper places in the solar system.

Nicolas Copernicus

Nicolas Copernicus

Copernicus reportedly had quite a bit of trouble seeing Mercury, as the smallest planet in the solar system is also the most elusive, dipping below the horizon faster than all the rest. Copernicus grumbled in one of his books that the ancient Egyptions had less trouble locating Mercury than he, since they didn’t live in a region blanketed by early morning fog. However, Ptolemy placed Venus closest to the Sun and Mercury to the Moon, while others claimed that Mercury and Venus were beyond the Sun.

In the Commentariolus, Copernicus postulated that, if the Sun is assumed to be at rest and if the Earth is assumed to be in motion, then the remaining planets fall into an orderly relationship whereby their sidereal periods increase from the Sun as follows: Mercury (88 days), Venus (225 days), Earth (1 year), Mars (1.9 years), Jupiter (12 years), and Saturn (30 years).

This theory did resolve the disagreement about the ordering of the planets but, in turn, raised new problems. To accept the theory’s premises, one had to abandon much of Aristotelian natural philosophy and develop a new explanation for why heavy bodies fall to a moving Earth.

It was also necessary to explain how a transient body like the Earth, filled with meteorological phenomena, pestilence, and wars, could be part of a perfect and imperishable heaven. In addition, Copernicus was working with many observations that he had inherited from antiquity and whose trustworthiness he could not verify. In constructing a theory for the precession of the equinoxes, for example, he was trying to build a model based upon very small, long-term effects. And his theory for Mercury was left with serious incoherencies.


We owe Copernicus our thanks for his tireless observations of the sky. Whenever you see Mercury in pictures or quickly ducking from the heavens to below the horizon, think of Copernicus and his attempts to scientifically explain the universe.


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