Seven planets of the Ptolemaic system—
Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn.
Six planets of the Copernican system—
Mercury, Venus, Earth, Mars, Jupiter, Saturn.
The five regular solids, in appropriate order—
Octahedron, Icosahedron, Dodecahedron, Tetrahedron, Cube.
| Table illustrating Kepler's third law. | ||||
| Planet. | Mean distance from Sun. D | Length of Year. T | Cube of the Distance. D3 | Square of the Time. T2 |
| Mercury | ·3871 | ·24084 | ·05801 | ·05801 |
| Venus | ·7233 | ·61519 | ·37845 | ·37846 |
| Earth | 1·0000 | 1·0000 | 1·0000 | 1·0000 |
| Mars | 1·5237 | 1·8808 | 3·5375 | 3·5375 |
| Jupiter | 5·2028 | 11·862 | 140·83 | 140·70 |
| Saturn | 9·5388 | 29·457 | 867·92 | 867·70 |
The length of the earth's year is 365·256 days; its mean distance from the sun, taken above as unity, is 92,000,000 miles.
LECTURE III
KEPLER AND THE LAWS OF PLANETARY MOTION
It is difficult to imagine a stronger contrast between two men engaged in the same branch of science than exists between Tycho Brahé, the subject of last lecture, and Kepler, our subject on the present occasion.
The one, rich, noble, vigorous, passionate, strong in mechanical ingenuity and experimental skill, but not above the average in theoretical and mathematical power.
The other, poor, sickly, devoid of experimental gifts, and unfitted by nature for accurate observation, but strong almost beyond competition in speculative subtlety and innate mathematical perception.