Dante’s moon does indeed give us a little trouble once or twice, but he never makes flagrant mistakes of this kind. His consistency and truth of description prove his knowledge of astronomy, and also imply intelligent thoughtful watching of the celestial movements; for it is notorious that book-knowledge, if unassisted by acquaintance at first-hand with the facts of a subject like astronomy, will not save a writer from glaring inaccuracies. His allusions to the motions of the moon, both diurnal and monthly, show plainly that he understood them well. His new moon appears in the evening, his waning moon rises late at night and sets in morning sunshine,[171] and his full moon comes on the meridian at midnight, for when he wishes to describe her at her brightest, as a comparison with a very brilliant light, he places her in a clear sky at midnight in her mid-month.[172] In the middle of a lunar month the moon is full, and being exactly opposite the sun will reach the meridian at midnight: this therefore is the time when she gives all the light she possibly can. In the _Quæstio_[173] Dante mentions that the moon does not move in the celestial equator, but sometimes north of it, and sometimes an equal amount south; in the _Convivio_ he indicates the length of her period, and briefly describes her phases and their cause—“Ora luce da un lato, e ora luce dall’ altro, secondo che ’l sole la vede.”[174] ------------------------------------------------------------------------ [171] _Inf._ xv. 18, 19; _Purg._ xviii. 76-81; _Purg._ x. 14, 15, _Cf._ ix. 44. [172] _Purg._ xxix. 53, 54. [173] _Qu._ xx. 61-63. [174] “Now she shines on one side, and now on the other, according to the way the sun looks upon her.” _Conv._ II. xiv. 77-79. ------------------------------------------------------------------------ Her position in the zodiac is mentioned several times. In one passage he indicates a very brief space of time in the following curious way:— “Quando ambo e due i figli di Latona, Coperti del Montone e della Libra, Fanno dell’ orizzonte insieme zona, Quant’ è dal punto che il zenit inlibra. Infin che l’uno e l’altro da quel cinto, Cambiando l’emisperio, si dilibra, Tanto, col volto di riso dipinto, Si tacque Beatrice.”[175] ------------------------------------------------------------------------ [175] “At what times both the children of Latona, Surmounted by the Ram and by the Scales, Together make a zone of the horizon, As long as from the time the zenith holds them In equipoise, till from that girdle both Changing their hemisphere disturb the balance, So long, her face depicted with a smile, Did Beatrice keep silence.” _Par._ xxix. 1-8. ------------------------------------------------------------------------