“Cerchiando il mondo.”[351] “Sotto il petto del Leone ardente.”[352]
Some of the most beautiful similes in the Divine Comedy are drawn from the planets. The angel-pilot of Purgatory, when first seen far off over the sea, is likened to the planet Mars, glowing red through morning mists, low in the west above the ocean floor;[353] and the angel that welcomes the poet to the second circle on the Mountain is beautiful as the Morning Star.
“A noi venia la creatura bella, Bianco vestita, e nella faccia quale Par tremolando mattutina stella.”[354]
Although any of the planets when rising just before the sun may be called a morning star, Venus is probably intended here, as also where St. Bernard, in his devotion to the Virgin, is compared with the Morning Star which takes its beauty from the sun:—
“Colui ch’abbelliva di Maria, Come del sole stella mattutina.”[355]
All the seven planets (that is, including sun and moon), are occasionally mentioned together, “tutti e sette,”[356] and their movement in the ecliptic is referred to in Par. x, 14: “L’obbliquo cerchio che i pianeti porta.”[357] In the 14th and 15th chapters of the second treatise of the Convivio, already so often quoted, Dante draws an elaborate comparison between the seven planets and the seven sciences of the Trivium and Quadrivium. The moon is Grammar, Mercury Dialectic, Venus Rhetoric, the Sun Arithmetic, Mars Music, Jupiter Geometry, and Saturn Astrology. The reasons given for the latter are the slow movement and the height (i.e. distance from Earth) of Saturn, which Dante compares with the length of the time taken in learning astronomy, and the loftiness of its subject.
In the same way the star sphere is said to resemble Physics and Metaphysics, the Primum Mobile Ethics, and the Empyrean Theology. The argument is very fanciful, but just what would appeal to readers of Dante’s day, who loved to find allegories everywhere; and it gives him an opportunity of instructing them very simply in his beloved science.
He sometimes uses the planetary periods as divisions of time (as Plato said they should be used), for computing earthly events, and in him this does not seem affectation, as it would with almost anyone else. It seems quite natural that Cacciaguida, when speaking in the heaven of Mars, and answering a question regarding the date of his birth, should count the time not by solar but by Martian years, saying that from the beginning of the Christian Era to the day of his birth, Mars had returned to his Lion (the constellation of Leo) five hundred and eighty times.[358] The length of the Martian year according to Alfraganus is 1 Persian year, 10 months, and 22 days nearly. The Persian year (as he tells us in the first chapter of the Elementa) consists of 12 months of 30 days each plus 5 extra days, making 365 days exactly (not 365¼ days like the Roman), so the Martian year is 687 days (the modern estimate is 686·9). 687 days × 580 gives us 1091 a.d. as the date of Cacciaguida’s birth. This is consistent with the date of his death, for he had just told Dante that he fell in the Crusade to which he followed the Emperor Conrad, and we know that this was fought in the year 1147.
Some commentators think that Dante did not intend the Martian year to be taken so precisely, but only as approximately two solar years, since he gave it thus in Conv. II. xv. 145. But there he specially states that he is quoting an approximate figure only (“uno anno quasi”[359] is half the period of Mars) whereas in the Paradiso it is used to fix a date. Since by taking 580 × 2 years we get 1160, an impossible date of birth for a man who died in 1147, the only way to support this theory that Dante was speaking loosely here is to adopt another reading of the passage, and substitute “tre” for “trenta.”[360] Then 553 (instead of 580) × 2 years would give the date 1106; but the reading is not supported by good authority.