CHAP. VII - URANUS AND NEPTUNE, THE ARCTIC PLANETS

Summary

A circumstance which is of great importance in considering the relations of the outer planets is apt to be lost sight of, owing to the unsatisfactory manner in which in nearly all books on astronomy the planetary orbits are represented. To look at the series of equidistant and concentric circles representing the orbits of the planets, who would suppose that in passing from the orbit of Jupiter to that of Saturn, a distance five times as great as that which separates our earth from the sun has to be traversed? But the distance separating Uranus from Saturn is twice as great even as this tremendous gap, while Neptune travels as far beyond Uranus as Uranus beyond Saturn. Nine hundred millions of miles in width is the enormous gap by which the path of Uranus is separated from that of the ringed planet on the inner side, and from that of distant Neptune on the outer, so that a line equal to the diameter of Jupiter's orbit would barely suffice to reach from Saturn to Uranus, or from Uranus to Neptune, even when either pair of planets are in conjunction.

We know so little of the physical aspect of Uranus and Neptune that it is extremely difficult to form any opinion as to their condition.