"...cosmos was complete. Its out limit was the stellar sphere. Just inside was Saturn, since it was the planet that took longest to move around the Zodiac. Next came Jupiter and Mars, set in order of decreasing orbital period, the time taken to make one complete orbit about the central Earth. Innermost was the Moon, since the lunar orbit placed it closest to us. The remaining three planets of Sun, Venus and Mercury, posed a problem. All three vagabond stars made their seeming journey about the Earth, in the same common time of one year."