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CHAP. 10. (13.)
ON THE RECURRENCE OF THE ECLIPSES OF THE SUN AND THE MOON.
It is ascertained that the eclipses complete their whole revolution in the space of 223 months, that the eclipse of the sun takes place only at the conclusion or the commencement of a lunation, which is termed conjunction, while an eclipse of the moon takes place only when she is at the full, and is always a little farther advanced than the preceding eclipse. Now there are eclipses of both these stars in every year, which take place below the earth, at stated days and hours; and when they are above it they are not always visible, sometimes on account of the clouds, but more frequently, from the globe of the earth being opposed to the vault of the heavens. It was discovered two hundred years ago, by the sagacity of Hipparchus, that the moon is sometimes eclipsed after an interval of five months, and the sun after an interval of seven; also, that he becomes invisible, while above the horizon, twice in every thirty days, but that this is seen in different places at different times. But the most wonderful circumstance is, that while it is admitted that the moon is darkened by the shadow of the earth, this occurs at one time on its western, and at another time on its eastern side. And farther, that although, after the rising of the sun, that darkening shadow ought to be below the earth, yet it has once happened, that the moon has been eclipsed in the west, while both the luminaries have been above the horizon. And as to their both being invisible in the space of fifteen days, this very thing happened while the Vespasians were emperors, the father being consul for the third time, and the son for the second.
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CHAP. 11. (14.)
OF THE MOTION OF THE MOON.
It is certain that the moon, having her horns always turned from the sun, when she is waxing, looks towards the east; when she is waning, towards the west. Also, that, from the second day after the change, she adds 47 1/2 minutes each day, until she is full, and again decreases at the same rate, and that she always becomes invisible when she is within 14 degrees of the sun. This is an argument of the greater size of the planets than of the moon, since these emerge when they are at the distance of 7 degrees only. But their altitude causes them to appear much smaller, as we observe that, during the day, the brightness of the sun prevents those bodies from being seen which are fixed in the firmament, although they shine then as well as in the night: that this is the case is proved by eclipses, and by descending into very deep wells.
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CHAP. 12. (15.)
OF THE MOTIONS OF THE PLANETS AND THE GENERAL LAWS OF THEIR ASPECTS.
The three planets, which, as we have said, are situated above the sun, are visible when they come into conjunction with him. They rise visibly in the morning, when they are not more than 11 degrees from the sun; they are afterwards directed by the contact of his rays, and when they attain the trine aspect, at the distance of 120 degrees, they take their morning stationary positions, which are termed pri- mary; afterwards, when they are in opposition to the sun, they rise at the distance of 180 degrees from him. And again advancing on the other side to the 120th degree, they attain their evening stations, which are termed secondary, until the sun having arrived within 12 degrees of them, what is called their evening setting becomes no longer visible. Mars, as being nearer to the sun, feels the influence of his rays in the quadrature, at the distance of 90 degrees, whence that motion receives its name, being termed, from the two risings, respectively the first and the second nonagenarian. This planet passes from one station to another in six months, or is two months in each sign; the two other planets do not spend more than four months in passing from station to station.
The two inferior planets are, in like manner, concealed in their evening conjunction, and, when they have left the sun, they rise in the morning the same number of degrees distant from him. After having arrived at their point of greatest elongation, they then follow the sun, and having overtaken him at their morning setting, they become invisible and pass beyond him. They then rise in the evening, at the distances which were mentioned above. After this they return back to the sun and are concealed in their evening setting. The star Venus becomes stationary when at its two points of greatest elongation, that of the morning and of the evening, according to their respective risings. The stationary points of Mercury are so very brief, that they cannot be correctly observed.
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CHAP. 13.
WHY THE SAME STARS APPEAR AT SOME TIMES MORE LOFTY AND AT OTHER TIMES MORE NEAR.
The above is an account of the aspects and the occultations of the planets, a subject which is rendered very complicated by their motions, and is involved in much that is wonderful; especially, when we observe that they change their size and colour, and that the same stars at one time approach the north, and then go to the south, and are now seen near the earth, and then suddenly approach the heavens. If on this subject I deliver opinions different from my predecessors, I acknowledge that I am indebted for them to those individuals who first pointed out to us the proper mode of inquiry; let no one then ever despair of benefiting future ages.
But these things depend upon many different causes. The first cause is the nature of the circles described by the stars, which the Greeks term apsides, for we are obliged to use Greek terms. Now each of the planets has its own circle, and this a different one from that of the world; because the earth is placed in the centre of the heavens, with respect to the two extremities, which are called the poles, and also in that of the zodiac, which is situated obliquely between them. And all these things are made evident by the infallible results which we obtain by the use of the compasses. Hence the apsides of the planets have each of them different centres, and consequently they have different orbits and motions, since it necessarily follows, that the interior apsides are the shortest.
(16.) The apsides which are the highest from the centre of the earth are, for Saturn, when he is in Scorpio, for Jupiter in Virgo, for Mars in Leo, for the Sun in Gemini, for Venus in Sagittarius, and for Mercury in Capricorn, each of them in the middle of these signs; while in the opposite signs, they are the lowest and nearest to the centre of the earth. Hence it is that they appear to move more slowly when they are carried along the highest circuit; not that their actual motions are accelerated or retarded, these being fixed and determinate for each of them; but because it necessarily follows, that lines drawn from the highest apsis must approach nearer to each other at the centre, like the spokes of a wheel; and that the same motion seems to be at one time greater, and at another time less, according to the distance from the centre.
Another cause of the altitudes of the planets is, that their highest apsides, with relation to their own centres, are in different signs from those mentioned above. Saturn is in the 20th degree of Libra, Jupiter in the 15th of Cancer, Mars in the 28th of Capricorn, the Sun in the 19th of Aries, Venus in the 27th of Pisces, Mercury in the 15th of Virgo, and the Moon in the 3rd of Taurus.
The third cause of the altitude depends on the form of the heavens, not on that of the orbits; the stars appearing to the eye to mount up and to descend through the depth of the air. With this cause is connected that which depends on the latitude of the planets and the obliquity of the zodiac. It is through this belt that the stars which I have spoken of are carried, nor is there any part of the world habitable, except what lies under it; the remainder, which is at the poles, being in a wild desert state. The planet Venus alone exceeds it by 2 degrees, which we may suppose to be the cause why some animals are produced even in these desert regions of the earth. The moon also wanders the whole breadth of the zodiac, but never exceeds it. Next to these the planet Mercury moves through the greatest space; yet out of the 12 degrees (for there are so many degrees of latitude in the zodiac), it does not pass through more than 8, nor does it go equally through these, 2 of them being in the middle of the zodiac, 4 in the upper part, and 2 in the lower part. Next to these
the Sun is carried through the middle of the zodiac, winding unequally through the two parts of his tortuous circuit. The star Mars occupies the four middle degrees; Jupiter the middle degree and the two above it; Saturn, like the sun, occupies two. The above is an account of the latitudes as they descend to the south or ascend to the north. Hence it is plain that the generality of persons are mistaken in supposing the third cause of the apparent altitude to depend on the stars rising from the earth and climbing up the heavens. But to refute this opinion it is necessary to consider the subject with very great minuteness, and to embrace all the causes.
It is generally admitted, that the stars, at the time of their evening setting, are nearest to the earth, both with respect to latitude and altitude, that they are at the commencement of both at their morning risings, and that they become stationary at the middle points of their latitudes, what are called the ecliptics. It is, moreover, acknowledged, that their motion is increased when they are in the vicinity of the earth, and diminished when they are removed to a greater altitude; a point which is most clearly proved by the different altitudes of the moon. There is no doubt that it is also increased at the morning risings, and that the three superior planets are retarded, as they advance from the first station to the second. And since this is the case, it is evident, that the latitudes are increased from the time of their morning risings, since the motions afterwards appear to receive less addition; but they gain their altitude in the first station, since the rate of their motion then begins to diminish, and the stars to recede.
And the reason of this must be particularly set forth. When the planets are struck by the rays of the sun, in the, situation which I have described, i. e. in their quadrature, they are prevented from holding on their straight forward course, and are raised on high by the force of the fire. This cannot be immediately perceived by the eye, and therefore they seem to be stationary, and hence the term station is derived. Afterwards the violence of the rays increases, and the vapour being beaten back forces them to recede.
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. 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.
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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, while they frequently return to the sun within this distance. 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. 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. 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. 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 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.
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CHAP. 15.
GENERAL LAWS 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, 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; 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. From this circumstance it was that the tale of Lynceus’s quick-sightedness originated. 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.
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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; 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, whic
h 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, 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 rendering them more feeble than when they fall upon her more directly. 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, 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.
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