This exists in a greater degree in their evening risings, the sun being then turned entirely from them, when they are drawn into the highest apsides; and they are then the least visible, since they are at their greatest altitude and are carried along with the least motion, as much less indeed as this takes place in the highest signs of the apsides. At the time of the evening rising the latitude decreases and becomes less as the motion is diminished, and it does not increase again until they arrive at the second station, when the altitude is also diminished; the sun’s rays then coming from the other side, the same force now therefore propels them towards the earth which before raised them into the heavens, from their former triangular aspect[232]. So different is the effect whether the rays strike the planets from below or come to them from above. And all these circumstances produce much more effect when they occur in the evening setting. This is the doctrine of the superior planets; that of the others is more difficult, and has never been laid down by any one before me[233].
CHAP. 14. (17.)—WHY THE SAME STARS HAVE DIFFERENT MOTIONS.
I must first state the cause, why the star Venus never recedes from the sun more than 46 degrees, nor Mercury more than 23[234], while they frequently return to the sun within this distance[235]. As they are situated below the sun, they have both of them their apsides turned in the contrary direction; their orbits are as much below the earth as those of the stars above mentioned are above it, and therefore they cannot recede any farther, since the curve of their apsides has no greater longitude[236]. The extreme parts of their apsides therefore assign the limits to each of them in the same manner, and compensate, as it were, for the small extent of their longitudes, by the great divergence of their latitudes[237]. It may be asked, why do they not always proceed as far as the 46th and the 23rd degrees respectively? They in reality do so, but the theory fails us here. For it would appear that the apsides are themselves moved, as they never pass over the sun[238]. When therefore they have arrived at the extremities of their orbits on either side, the stars are then supposed to have proceeded to their greatest distance; when they have been a certain number of degrees within their orbits, they are then supposed to return more rapidly, since the extreme point in each is the same. And on this account it is that the direction of their motion appears to be changed. For the superior planets are carried along the most quickly in their evening setting, while these move the most slowly; the former are at their greatest distance from the earth when they move the most slowly, the latter when they move the most quickly. The former are accelerated when nearest to the earth, the latter when at the extremity of the circle; in the former the rapidity of the motion begins to diminish at their morning risings, in the latter it begins to increase; the former are retrograde from their morning to their evening station, while Venus is retrograde from the evening to the morning station. She begins to increase her latitude from her morning rising, her altitude follows the sun from her morning station, her motion being the quickest and her altitude the greatest in her morning setting. Her latitude decreases and her altitude diminishes from her evening rising, she becomes retrograde, and at the same time decreases in her altitude from her evening station.
Again, the star Mercury, in the same way, mounts up in both directions[239] from his morning rising, and having followed the sun through a space of 15 degrees, he becomes almost stationary for four days. Presently he diminishes his altitude, and recedes from his evening setting to his morning rising. Mercury and the Moon are the only planets which descend for the same number of days that they ascend. Venus ascends for fifteen days and somewhat more; Saturn and Jupiter descend in twice that number of days, and Mars in four times. So great is the variety of nature! The reason of it is, however, evident; for those planets which are forced up by the vapour of the sun likewise descend with difficulty.
CHAP. 15.—GENERAL LAWS[240] OF THE PLANETS.
There are many other secrets of nature in these points, as well as the laws to which they are subject, which might be mentioned. For example, the planet Mars, whose course is the most difficult to observe[241], never becomes stationary when Jupiter is in the trine aspect, very rarely when he is 60 degrees from the sun, which number is one-sixth of the circuit of the heavens[242]; nor does he ever rise in the same sign with Jupiter, except in Cancer and Leo. The star Mercury seldom has his evening risings in Pisces, but very frequently in Virgo, and his morning risings in Libra; he has also his morning rising in Aquarius, very rarely in Leo. He never becomes retrograde either in Taurus or in Gemini, nor until the 25th degree of Cancer. The Moon makes her double conjunction with the sun in no other sign except Gemini, while Sagittarius is the only sign in which she has sometimes no conjunction at all. The old and the new moon are visible on the same day or night in no other sign except Aries, and indeed it has happened very seldom to any one to have witnessed it. Prom this circumstance it was that the tale of Lynceus’s quick-sightedness originated[243]. Saturn and Mars are invisible at most for 170 days; Jupiter for 36, or, at the least, for 10 days less than this; Venus for 69, or, at the least, for 52; Mercury for 13, or, at the most, for 18[244].
CHAP. 16. (18.)—THE REASON WHY THE STARS ARE OF DIFFERENT COLOURS.
The difference of their colour depends on the difference in their altitudes; for they acquire a resemblance to those planets into the vapour of which they are carried, the orbit of each tinging those that approach it in each direction. A colder planet renders one that approaches it paler, one more hot renders it redder, a windy planet gives it a lowering aspect, while the sun, at the union of their apsides, or the extremity of their orbits, completely obscures them. Each of the planets has its peculiar colour[245]; Saturn is white, Jupiter brilliant, Mars fiery, Lucifer is glowing, Vesper refulgent, Mercury sparkling, the Moon mild; the Sun, when he rises, is blazing, afterwards he becomes radiating. The appearance of the stars, which are fixed in the firmament, is also affected by these causes. At one time we see a dense cluster of stars around the moon, when she is only half-enlightened, and when they are viewed in a serene evening; while, at another time, when the moon is full, there are so few to be seen, that we wonder whither they are fled; and this is also the case when the rays of the sun, or of any of the above-mentioned bodies[246], have dazzled our sight. And, indeed, the moon herself is, without doubt, differently affected at different times by the rays of the sun; when she is entering them, the convexity of the heavens[247] rendering them more feeble than when they fall upon her more directly[248]. Hence, when she is at a right angle to the sun, she is half-enlightened; when in the trine aspect, she presents an imperfect orb[249], while, in opposition, she is full. Again, when she is waning, she goes through the same gradations, and in the same order, as the three stars that are superior to the sun[250].
CHAP. 17. (19.)—OF THE MOTION OF THE SUN AND THE CAUSE OF THE IRREGULARITY OF THE DAYS.
The Sun himself is in four different states; twice the night is equal to the day, in the Spring and in the Autumn, when he is opposed to the centre of the earth[251], in the 8th degree of Aries and Libra[252]. The length of the day and the night is then twice changed, when the day increases in length, from the winter solstice in the 8th degree of Capricorn, and afterwards, when the night increases in length from the summer solstice in the 8th degree of Cancer[253]. The cause of this inequality is the obliquity of the zodiac, since there is, at every moment of time, an equal portion of the firmament above and below the horizon. But the signs which mount directly upwards, when they rise, retain the light for a longer space, while those that are more oblique pass along more quickly.