Nicolas Copernicus  (1473 – 1543)

 

Nicolas Copernicus was born in Torun, Poland in 1473 and died in 1543.  He studied both law and medicine in Italy, but spent most of his life as Cannon of Frombork Cathedral in Poland.  He published his great work “On the Revolutions of the Heavenly Spheres” in 1543, the year he died.  In this book he detailed a heliocentric system (sun centered) and described advantages it had over the geocentric system of Ptolemy.  Over the space of about 75 years, this new view of the solar system gradually gained acceptance throughout Europe. 

 

Copernicus’ system:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Main features:

 

  1. Planets move in circular orbits around the sun
  2. Earth is one of the planets
  3. Night and day on the earth are due to the rotation of the earth on its axis (one rotation every 24 hours).
  4. The apparent motion of the sun along the ecliptic is due to the revolution of the earth around the sun (one complete revolution in one year).
  5. Retrograde motion of the planets is an illustion produced by the earth passing the planets as it journeys around the sun (much like the way the car you pass on the freeway seems to be moving backward relative to your car.)
  6. Mercury and Venus are always found close to the sun because their orbits lie between the earth and the sun
  7. The scale of the solar system can be established in astronomical units (AU – the distance from the earth to the sun).  Using the inner planets this is accomplished as in the following diagram:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


This is how it works:  When Venus is at its maximum distance from the sun, the triangle defined by the sun, the earth and Venus is as shown above.  The angle α is known because that is the angular distance between Venus and the sun as viewed from the earth.  Geometrical theorems can show that the angle at Venus is always 90 degrees when α  is a maximum.  The length of the hypotenuse of this right triangle is one AU by definition.  Knowing all the angles and one side of a triangle allows us to determine the length of all the other sides,  in this case the distance from Earth to Venus and Venus to the sun.

 

Scholars were initially attracted to Copernicus’ system because it  (1) it explained retrograde motion in an elegant way (2) it explained why Mercury and Venus were always close to the sun, and (3) it provided a way for establishing the scale of the solar system.  There were, however, two drawbacks: (1) it was hard to explain physically (for example, why don’t we notice that the earth is moving?) and (2) although elegant, it didn’t predict the future position of the planets any better than Ptolemy’s system.