History of Science 3013: Exercise 6

Peter Barker

Spheres and orbs in Copernicus

Question 1: Using an 8.5x11 inch sheets of graph paper and a compass, draw Copernicus' cosmic scheme to scale using the figures indicated below. Label the spherical shell -- or orb -- corresponding to each object, in the correct order. (Ptolemy's figures from Exercise 5 are given for comparison.)
Planet Relative Distance Ptolemy Copernicus
Earth greatest 1.04
least 0.96
Jupiter greatest 14.4 5.46
least 8.8 4.98
Mars greatest 8.8 1.67
least 1.2 1.38
Mercury greatest 0.2 0.49
least 0.06 0.3
Saturn greatest 20.1 9.7
least 14.4 8.66
Sun greatest 1.2
least 1.1
Venus greatest 1.1 0.76
least 0.2 0.68
Hint: In each case find the largest distance first, and use that to select a scale that will fit your paper. It may be easiest to place the center of the system on the left edge of the paper and draw half or less of each orb.-- but some people have drawn the whole thing.

Question 2: On the sheet provided, figures 2A and 2B show Ptolemy's Almagest model for the sun and for the moon, with the corresponding three-dimensional orb models. Figures 2C and 2D show Copernicus's models for the moon and for an outer planet. What would the corresponding orb models look like?