7.3 Saturn

To all serious observers of the heaven, it was known that stars move in a fixed formation around the Earth except for seven bodies that moved through the fixed stars in a wide band, the zodiac. To the Greeks, all heavenly bodies were stars; most were fixed but some wandered. These seven wandering stars, or planets, were (in the conventional order), Moon , Mercury, Venus, Sun, Mars, Jupiter, Saturn. Mercury was the most difficult to observe because it was always close to the Sun, Venus, as morning or evening star, was the brightest body in the heavens. Mars had a distinctive red color, Jupiter at opposition was very bright, and the straw-colored Saturn, the slowest of all planets ( sidereal period 30 years), was the dimmest. The planets were identified with gods by the Mesopotamians, and the Greeks copied this system, assigning planets the names of their gods. The planets were also associated with the seven known metals: Moon/silver, Mercury/mercury, Venus/copper, Sun/gold. Mars/iron, Jupiter/tin, and Saturn/lead. In accordance with their gods, the planets were assigned astrological meanings still used by the astrologers who write daily columns in many of our newspapers.

Saturn, associated with time and the grim reaper, was usually depicted with a scythe. According to the prevailing cosmology of Aristotle, Western astronomers knew that, like all other heavenly bodies, the planet Saturn was perfect and spherical. The telescope therefore gave them a surprise. After publishing Sidereus Nuncius , in March 1610, Galileo continued scrutinizing the heavens, especially the planets, in the hope of making further discoveries. In July, as Saturn was bright in the evening sky and approaching opposition,

I discovered another very strange wonder, which I should like to make known to their Highnesses . . . , keeping it secret, however, until the time when my work is published . . . . the star of Saturn is not a single star, but is a compsite of three, which almost touch each other, never change or move relative to each other, and are arranged in a row along the zodiac, the middle one being three times larger than the lateral ones, and they are situated in this form: oOo.

Galileo no doubt planned to publish this new discovery in his next book, but in the meantime, how could he preserve his priority and prevent others from claiming the discovery as their own? His solution was to circulate an anagram, s m a i s m r m i l m e p o e t a l e u m i b u n e n u g t t a u i r a s. Others would know that he had discovered something and when he had discovered it, but they would not known what the discovery was. The number of letters in the anagram, 37, was too small to allow him later to fudge and change the solution to describe a discovery made by someone else in the meantime. Before the days of scientific papers (invented in the 1660s) this was an effective (if not always foolproof) method of claiming priority.