The allusions to sun, moon, and stars in the Divine Comedy, when thus brought together, are seen to follow one another according to a regular scheme, and they form a very good guide by which to time Dante on his journey. There is a little inaccuracy in one passage about the stars, and the moon is ambiguous once, but quite explicable. Taking the allusions in a simple popular sense, as he seems to intend us to do, assuming that the signs and the constellations of the zodiac are identical, and that the moon, which at first is opposite the sun, traverses about 13° in the zodiac daily, and loses about an hour of time more or less, there is very little difficulty in following him. It is quite enough to know that the sun is somewhere in Aries throughout, and that the moon is therefore in Libra at the beginning.

But if we wish to know a little more accurately the positions of sun and moon among the stars, we must carefully compare the passages bearing on this question. Commentators differ so much that while some think the sun’s annual motion is ignored, and it is assumed to be at the equinox all the time, others maintain that it was at the equinox on the first day and moved on through Aries at the rate of about one degree a day (as it should do, since there are 365 days in a year and 360° in the circumference of the sphere);[512] while others again say that it was merely somewhere in Aries from the beginning.

What are the actual indications of its position? No one questions that it was in Aries throughout the Vision, for this is often indicated, sometimes directly, as in Inf. i. 38-40, sometimes by mentioning Taurus as the sign following the sun,[513] or Pisces as the sign preceding.[514]

There are four detailed descriptions:—

(1) On the first morning, the sun rose among those stars which were with him at the Creation.[515] As we have seen, this may mean merely some point in Aries, or the first point of Aries, at which the sun was thought to have been placed when created.

(2) On the seventh day it rose near a point where three crosses are formed by the intersection of four circles.[516] One naturally thinks of the horizon as one of these circles; the equator and ecliptic, whose intersection define the equinox, suggest themselves as two more; the fourth is doubtless the colure which passes through the equinoctial points and the poles, although curiously enough this is not mentioned by Ptolemy or Alfraganus, who only speak of the solstitial colure. Fig. 51 shows how the horizon makes a cross with each of the other three when the equinox is upon it. The sun is at the point of intersection when rising with the equinox, and it was near there when it rose this morning—“quasi.” It was therefore near, but not exactly at the equinox, and we know that it was the vernal, not the autumnal equinox, from the many allusions to Aries.

(3) When Dante rises to the sun (on the same day) he directs our attention once more to this point where “the one motion strikes the other,” that is, where the ecliptic—the oblique circle which bears the planets—branches off from the equator, and he reminds us of the supreme importance of this divergence. The sun, he says, was in this place. He does not mean at the exact point of intersection, or this passage would be in flat contradiction to the last: “quella parte”[517] is no more precise than “quelle stelle,”[518] and means only this part of the sky, or the constellation of Aries. The words which follow not only specify that it was the spring equinox, but suggest that the sun had already traversed several of those spirals which bring him to us earlier each morning, i.e. it was several days after the equinox.[519]

(4) On the same day the sun was “one sign and more” removed from some point in Gemini.[520] This is very vague, but at least the sun cannot now have been at the first point of Aries, or it would have been two whole signs from even the first degree of Gemini.

It seems, then, that we cannot possibly agree that the sun was at the equinox throughout the poem. It is clear that it was past the equinox towards the end; but from these four passages we cannot be sure whether it was there on the first morning, or whether it moved through some undefined part of Aries during the Vision.

One consideration gives us some help, however. We know from Inf. xxi. 112-114 that the first day was either March 25, which was believed in the Middle Ages to be the true anniversary of the Crucifixion, or Good Friday, which was kept by the Church as such. March 25 is four days after the date which the Church still kept as the day of the Equinox (March 21), and 13 days after the true equinox, which at this time fell on March 12. Good Friday also almost inevitably must fall after the equinox, since Easter follows the full moon which follows the equinox. It is true that some of Dante’s readers may still have regarded the old traditional date of March 25 as the true day of the equinox, and possibly it was to suit all shades of knowledge that he left the sun’s position vague; but he himself certainly knew better, and probably had March 12 in his mind. Then those who held to March 25 might consider the sun as exactly at the equinox on the first day of the Vision, but all better-informed readers and Dante himself must have regarded it as somewhat past this point. If we take it that, e.g., it was a week past the equinox, the sun was in about 7° of Aries, and this position agrees with the four crucial passages mentioned above. The stress laid on the equinox seems to demand that the sun should be at least as near it as this on the first day; and a week later it would have reached the middle of Aries, which is the position we assigned to it from a discussion of Par. xxvii. 86, 87.

This also agrees well with the course of the moon in the zodiac, which must depend upon the sun’s. We have seen that she was opposite the sun on the first morning, that her light paled the first-risen stars of Scorpio while she was yet beneath the eastern horizon three days later, and that she was proceeding south on the following night. If the sun was in the 7th degree of Aries on the first morning, the moon must have been in the 7th degree of Libra; her mean daily motion of 13° would bring her to the 16th degree of Scorpio three days later and to the last degree on the day following; so even if we allow a deviation of a few degrees from the average, she was just where she should have been on each occasion. We have assumed for convenience that she became full and was opposite the sun just as she set on the first morning, but this may have happened at any time during the previous night (in the Forest): Dante has not specified the hour, and it is of no consequence, since the indications of time by the moon must necessarily be vague.

The time of sunrise will still differ little from 6 o’clock, a week after the equinox. In London it is a quarter of an hour earlier, but the difference is less in Italy, and still less in the latitude of Jerusalem.

Besides the sun and moon, two of the planets are mentioned as in a particular place among the stars.

Venus, before sunrise on the fourth morning, is seen among the stars of Pisces;[521] and she is also mentioned as a morning star before sunrise on the seventh day.[522]

Saturn is in Leo. “Il petto del Leone”[523] may mean the western part of the Lion, the part which first rises and contains the head and breast, or it may refer to the star Regulus, which is called by Ptolemy and Alfraganus “Cor Leonis.”[524] “Sotto il petto”[525] may mean the position of the planet as seen projected in the sky or a map, that is, a little south of this part of the constellation; more probably, perhaps, Dante is thinking of the supposed position of Saturn’s sphere below that of the stars.[526]

Mars is spoken of as having returned to his own Lion a number of times: “al suo Leon ... venne,”[527] but this does not necessarily imply that he was in that constellation at the time.

Mercury and Jupiter are not noted as seen anywhere in the sky, nor does Dante say in what constellation they were when he entered them with Beatrice.

There are a number of pitfalls into which Dante might have stumbled, with this disposition of the skies, and the change to the southern hemisphere; and that he has avoided all is as clear a proof of his familiarity with astronomical phenomena as the positive evidence of his truthful, consistent descriptions. For instance, he might very well have represented the cold planet Saturn as actually aiding the cold moon in driving away the heat of the day during the night, in Purg. xix. 1-3, instead of only saying “talor da Saturno;”[528] but if so, this would have been inconsistent with the position of Saturn in Leo, since Leo was below the horizon when dawn was drawing near and Pisces was rising. Again, we have already mentioned that he evidently did not forget that it was autumn in the southern hemisphere. He never suggests that it was spring in Purgatory, and in the passage quoted above, where he describes sunrise at the March equinox, saying that the sun then moves “con miglior corso e con migliore stella,”[529] this happiest effect on the world is restricted to “mortals,” who as he thought all dwelt in the northern hemisphere, “surge ai mortali.”[530] I do not mean that the expression was used for this reason, but it is an example of how instinctively he avoided mistakes into which any other author would almost certainly have fallen.