Page:The Solar System - Six Lectures - Lowell.djvu/113



red. Jupiter, however, we see much the better of the two, and we may describe it as typifying both.

Both are bulky; their masses to their volumes being such that their mean densities are respectively somewhat greater (1.28%) and somewhat less than water (.69%). Both are in rapid rotation; particles on their equators traveling with speeds comparable with their orbital velocities. Both, in consequence, are strikingly flattened into oblate spheroids whose elliptic curves instantly strike the eye. In the disks of both we look only upon atmosphere and cloud. Lack of solidity, speed of self-movement, cloudy condition, are all so many signs of—youth. In relative—if not in absolute—age, both planets are still very young.

Semi-suns in several senses, the two planets are three-quarters way in their journey from nebula to world. In their traits both more closely resemble the Sun than the Earth. Indeed, with the trifling exception of not shining, the disk of Jupiter or of Saturn bears a very remarkable analogy to the solar.

In a large telescope and in good seeing, Jupiter is a color-picture as beautiful as it is marked. A deep pink flush suffuses the planet's equatorial regions. It probably betokens the parts of the