PLINY2-1

PLINY'S NATURAL HISTORY

Book II

Chapters VIII - XVII

VIII. This theory leads mortal minds upward to heaven, and discloses to their observation from that height, as it were, the greatness of the three greatest
parts of the universe; clearly it would not be possible for the whole of the sun to be eclipsed from the earth by the passage of the moon between them if the earth were larger than the moon. The vast size of the sun will be shown with the more certainty from the two bodies, so that there is no need to investigate its size by the evidence of the eyes and by logical inference arguing that it is immeasurably large for the following reasons: (1) the shadow that it throws of rows of trees along the balks of fields are at equal distances apart for ever so many miles, just as if over the whole space the sun were in the centre; a (2) during the equinoxes it reaches the vertical simultaneously for all the inhabitants of the southern region; (3) the shadows of the people living round the Tropic of Cancer fall northward at midday but westward at sunrise, which could not happen unless the sun were much larger than the earth; (4) when it is rising its breadth exceeds Mount Ida, overlapping it widely right and left - and that though it is separated from it by so great a distance.
The eclipse of the moon supplies indubitable proof of the size of the sun, just as the sun itself when it suffers eclipse proves the smallness of the earth. For shadows are of three shapes, and it is clear that, if the solid object that throws a shadow is equal in area to the shaft of light, the shadow projected is shaped like a pillar and is of infinite length, but if the solid body is larger than the light, the shadow has the shape of an upright spinning-top, so that it is narrowest at the bottom, and infinite in length as in the former case, while if the solid is smaller than the light the result is the figure of a cone narrowing down to end in a point, and this is t he nature of the shadow observed during an eclipse of the moon; hence it is proved without any further possibility of doubt remaining that the sun exceeds t he earth's size. Indeed, this is also proved by the silent testimony of nature herself; for why in the [ division of the turns of the year does the winter sun retire, so as to refresh the earth with the darkness of the nights? when otherwise it would unquestionably scorch up the earth, and even as it is does so in a certain part, so great is its magnitude.

The stars - their magnituge
Astronomical discoveries

IX. The first person indeed of Roman nationality who published an explanation of both kinds of eclipse was Sulpicius Gallus - the colleague in the consulship of Marcus Marcellus, but at the time military tribune - who delivered the army from fear when on the day before the defeat a of King Perseus by Paulus he was brought before an assembly by the commander-in-chief to foretell an eclipse, and later also by writing a treatise. The original discovery was made in Greece by Thales of Miletus, who in the fourth year of the 48th Olympiad (585 B.C.) foretold the eclipse of the sun that occurred in the reign of Alyattes, in the 170th year after the foundation of Rome. After their time the courses of both stars for 600 years were prophesied by Hipparchus, whose work embraced the calendar of the nations and the situations of places and aspects of the peoples - his method being, on the evidence of his contemporaries, none other than full partnership in the designs of nature. O mighty heroes, of loftier than mortal estate, who have discovered the law of those great divinities and released the miserable mind of man from fear, mortality dreading as it did in eclipses of the stars crimes or death of some sort (those sublime singers, the bards Stesichorus and Pindar, clearly felt this fear owing to an eclipse of the sun), or in the dying of the moon inferring that she was poisoned and consequently coming to her aid with a noisy clattering of cymbals (this alarm caused the Athenian general Nicias, in his ignorance of the cause, to be afraid to lead his fleet out of harbour, so destroying the Athenians' resources): all hail to your genius, ye that interpret the heavens and grasp the facts of nature, discoverers of a theory whereby you have vanquished gods and men! for who beholding these truths and the regularity of the stars' periods of trouble (for so it has pleased you to call them), would not forgive his own destiny for the generation of mortals?
Now I will briefly and summarily touch on facts that are admitted about the same matters, giving an account of them only at necessary points and in a cursory manner, because such theorising does not form part of the task that I have set in hand, and also it is less surprising that explanations cannot be produced for all the facts than that agreement has been reached on some of them.

X. It is certain that eclipses recur in cycles of 223 months - eclipses of the sun only when the moon is in her last or first phase (this is called their
'conjunction'), eclipses of the moon only at full moon - and always within the period of their last occurrence; but that yearly at fixed days and hours
eclipses of either star occur below the earth, and that even when they occur above the earth they are not visible everywhere, sometimes owing to clouds, more often because the earth's globe stands in the way of the world's curvature. Less than 200 years ago the penetration of Hipparchus discovered that an eclipse of the moon also sometimes occurs four months after the one before and an eclipse of the sun six months, and that the latter when above earth is hidden twice in thirty days, but that this eclipse is visible to different nations, and - the most remarkable features of this remarkable occurrence - that when it comes about that the moon is obscured by the shadow of the earth, this sometimes happens to it from the west side and sometimes from the east; and he also discovered for what exact reason, although the shadow causing the eclipse must from sunrise onward be below the earth, it happened once in the past that the moon was eclipsed in the west while both luminaries were visible above the earth. For the eclipse of both sun and moon within 15 days of each other has occurred even in our time, in the year of the third consulship of the elder Emperor Vespasian and the second consulship of the younger.

XI. It is unquestionable that the moon's horns are always turned away from the sun, and that when waxing she faces east and when waning west; and that the moon shines 47 1/2 minutes longer daily from the day after new moon to full and 472 minutes less daily to her wane, while within 14 degrees of the sun she is always invisible. This fact proves that the planets are of greater magnitude than the moon, since these occasionally become visible even on reaching 7 degrees' distance; but their altitude makes them appear smaller, just as the sun's radiance makes the fixed stars invisible in daytime, although they are shining as much as in the night, which becomes manifest at a solar eclipse and also when the star is reflected in a very deep well.

The moon's motions

XII. The three planets whose positions we have stated to be above the sun travel with the sun when they set and are never more than 11 degrees separate from the sun at dawn when they rise. Afterwards they retire from contact with his rays, and make their morning or ' first ' stations in a triangle 120 degrees away, and subsequently their evening risings opposite 180 degrees away, and again approaching from the other side, make their evening or ' second ' stations 120 degrees away, till the sun overtaking them at 12 degrees obscures them - this is called their evening setting. The planet Mars being nearer feels the sun's rays even from its quadrature, at an angle of 90 degrees, which has given to his motion after each rising the name of ' first' or ' second ninety-degree.' At the same time Mars remains stationary in the signs of the zodiac for periods of six months (otherwise having a two-month period), whereas Jupiter and Saturn spend less than four months in each station. The two lower planets (Mercury and Venus) are similarly obscured at their evening conjunction, and when left by the sun make their morning rising the same number of degrees away, and from the further limits of their distance follow the sun and when they have overtaken him are hidden in their morning setting and pass away. Then they rise in the evening at the same distance apart, as far as the limits we have stated. From these they pass backward to the sun, and disappear in their evening setting. The planet Venus actually makes two stations, morning and evening, after each rise, from the furthest limits of her distance. Mercury's stations have too short a period to be perceptible.

Motions of the plantets
Theory of their light
Causes of apparent recession and approach
General properties of planets
Reasons for changes of colour

XIII. This is the system of the shining and occultation of the planets: it is more complicated from their motion and involves many remarkable facts, inasmuch as they change their magnitude and their colours, and both approach the North and retire towards the South, and suddenly are seen closer to the earth or to the sky. And although our account of these matters will differ in many points from that of our predecessors, we confess that credit for these points also must be given to those who first demonstrated the methods of investigating them: only nobody must abandon the hope that the generations are constantly making progress.
All these occurrences are due to a plurality of causes. The first is the factor of the circles which in the case of the stars the Greeks designate apsides or arcs (it will be necessary to employ Greek terms). Each planet has its own circle, and these are not the same as those of the firmament, since the earth between the two vertices, named in Greek poles, is the centre of the sky, and also of the zodiac, which is situated on a slant between the poles. [All these facts are always established beyond doubt by the method of compasses.] Therefore the special arc of each is drawn from a different centre, and consequently they have different orbits and dissimilar motions, because the inner arcs must necessarily be shorter.
It follows that the points of the arcs highest above the centre of the earth are: in the case of Saturn in Scorpio, in that of Jupiter in Virgo, of Mars in Leo, of the sun in the Twins, of Venus in the Archer, of Mercury in Capricorn, of the moon in the Bull, at the middle of each, and the points lowest and nearest to the centre of the earth are opposite. The result of this is that they appear to move slower and to be smaller when they are travelling at the highest point of their circuit, but to be larger and travel faster when they have come nearer to the earth, not because they actually accelerate or reduce their natural motions, which are fixed and individual to them, but because lines drawn from the top of the arc to the centre necessarily converge like the spokes of a wheel, and the same motion at one time is perceived as faster and at another slower according to its distance from the centre.
Another reason of their elevations is because they have the points of their arcs highest from their centre in different signs - Saturn in the 20th degree of the Scales, Jupiter in the 15th of the Grab, Mars in the 28th of Capricorn, the sun in the 29th of the Ram, Venus in the 27th of the Fishes, Mercury in the 15th of Virgo, the moon in the 4th of the Bull.
A third explanation of their altitudes is explained by the dimensions of the firmament, not that of a circle, the eye judging them to rise or to sink through the depth of the air.
Linked with this is the cause of the latitudes of the zodiac and of its obliquity. The stars we have mentioned travel through the zodiac, and the only
habitable part of the earth is what lies beneath it - all the other parts towards the poles are frost-bound. Only the planet Venus goes two degrees outside the zodiac; this is understood to be the reason that causes some animals to be born even in the desert places of the world. The moon also wanders through the whole of its breadth, but without going at all outside it. The planet Mercury diverges very widely from these, but without wandering over more than
8 of the 12 degrees of latitude of the zodiac, and these 8 not uniformly but two in the middle of the zodiac, four above it and two below it. Then the sun travels unevenly in the middle of the zodiac between the two halves with a wavy serpentine course, the planet Mars over 4 degrees in the middle, Jupiter one in the middle and two above it, Saturn two like the sun. This will be the principle of the latitudes of the planets when setting towards the South or rising towards the North. Most people have supposed that with this system agrees also the third mentioned above, that of their rising from the earth to the sky, and that this ascent also is made simultaneously; but this is a mistake. To refute them it is necessary to develop an extremely abstruse argument that embraces all the causes mentioned. It is agreed b that the planets are nearest to the earth in both altitude and latitude at their evening setting, and that their morning risings occur at the beginning of both altitude and latitude, while their stations occur in the middle sections of the altitudes, called 'ecliptics.' It is similarly admitted that their velocity increases as long as they are in the neighbourhood of the earth and decreases when they withdraw from it to a height: this theory is specially supported by the apogees of the moon. It is equally undoubted that the three higher ones moreover increase their motion in their morning risings and diminish it from their first (morning) stations to their second (evening) stations. In view of these facts it will be evident that the latitudes are ascended from their morning rising, because in that state their acceleration first begins to diminish, but in their first stations their altitude also is ascended, since then the numbers first begin to be reduced and the stars begin to recede. The reason for this must especially be given. When struck in the degree that we stated and by a triangular ray of the sun they are prevented from pursuing a straight course, and are lifted upward by the fiery force. This cannot be directly perceived by our sight, and therefore they are thought to be stationary, which has given rise to the term 'station.' Then the violent force of the same ray advances and compels them by the impact of the heat to retire. This occurs much more at their evening rising, when they are driven out to the top of their apsides by the full opposing force of the sun, and appear very small because they are at the distance of their greatest altitude and are moving with their smallest velocity - which is proportionately smaller when this occurs in the highest signs of their apsides. From their evening rise their altitude is descended with a velocity now decelerating less and less, but not accelerating before their second stations, when their altitude also is descended, the ray passing above them from the other side and pressing them down again to the earth with the same force as that with which it had raised them to the sky from the former triangle. So much difference does it make whether the rays come from below or from above, and the same things occur far more in the evening setting.
This is the theory of the higher stars; that of the rest is more difficult and has been explained by nobody before ourselves.

XIV. First therefore let us state the reason why Venus never departs more than 46 degrees and Mercury never more than 23 degrees from the sun, and why they often retire and return towards the sun within those limits. As situated below the sun both have arcs that are the opposite of those of the other planets, and as much of their circle is below the earth as that of the planets mentioned before is above it; and they cannot be further from it than they are because the curve of their arcs does not allow greater elongation there; consequently the edges of their arcs put a limit on a similar principle for each, and compensate for the dimensions of their longitude by the enlargement of their latitude. But, it will be objected, why do they not reach 46 and 23 degrees always? As a matter of fact they do, but the explanation escapes the theorists. For it is manifest that even their arcs alter, because they never cross the sun; accordingly when the edges have fallen on one side or the other into the actual degree of the sun, then the stars also are understood to have reached their longest distances, but when the edges are short of that, they themselves too are compelled to return with proportionately greater velocity, since with each of them that is always the extreme limit.
This also explains the contrary principle of their motions. For the higher planets travel most quickly in their evening setting, whereas these travel most slowly, and the former are farthest from the earth when their pace is slowest but the latter are highest when their pace is quickest - the reason being that with the latter the circumference of the circle accelerates their pace in the same manner as proximity to the centre does in the case of the former; the former begin to decelerate from their morning setting, but the latter to accelerate. The former travel backward from their morning to their evening station, the planet Venus from her evening to her morning station. But she begins to climb her latitude after her morning rise, but after her morning station to ascend her altitude and follow the sun, being swiftest and highest at her morning setting; whereas she begins to descend in latitude and decelerate after her evening rising, and to turn back and simultaneously to descend in altitude after her evening station; on the other hand the planet Mercury begins to climb in both ways after his morning rising, but after his evening rising to descend in latitude, and following the sun at an interval of 15 degrees he stands motionless for almost four days. Afterwards he descends from his altitude and proceeds back from his evening setting to his morning rise. And only this planet and the moon set in as many days as they have risen in; Venus ascends in 15 times as many days as she sets in, while Saturn and Jupiter descend in twice as many, and Mars in actually four times as many. So great is the variety of nature; but the reason is evident - bodies that strain up into the heat of the sun also have difficulty in descending.

XV. Many more facts can be produced about these mysteries of nature and the laws that she obeys - for example, in the case of the planet Mars (whose course it is very difficult to observe) that it never makes its station with Jupiter at an angle of 120°, and very seldom with Jupiter separated 60° (which amounts to 1/6 of the celestial sphere, and never makes its rises simultaneously with Jupiter except in two signs only, Cancer and Leo, whereas the planet Mercury rarely makes its evening rises in Pisces, and most frequently in Virgo, its morning rises in Libra, and also its morning rises in Aquarius, very rarely in Leo; it does not make its return in Taurus and in Gemini, and not below the 25th degree in Cancer; Gemini is the only sign in which the moon makes conjunction with the sun twice, Sagittarius the only one in which she does not meet him at all, Aries the only one in which the old moon and the new moon are visible on the same day or night (and this too it has happened to few mortals to see, hence Lynceus's reputation for keen sight); the longest period of invisibility for the planets Saturn and Mars is 170 days, for Jupiter 36 days; the shortest periods for all these are 10 days less; Venus's period is 69 days or at shortest 52, Mercury's 13 or at longest 17.

XVI. The colours of the planets vary with their colours of altitudes, inasmuch as they are assimilated to the stars into whose atmosphere they come in rising, and the circuit of another's path modifies their colour in either direction as they approach, a colder circuit to pallor, a hotter one to redness, a windy one to a leaden colour, the sun and the intersection of its orbit with theirs, and also the extremities of their paths, changing them to black darkness. It is true that each has its own special hue - Saturn white, Jupiter transparent, Mars fiery, Lucifer bright white, Vesper glaring, Mercury radiant, the moon soft, the sun when rising glowing and afterwards radiant; with these being causally connected also the appearance of the fixed stars. For at one time there is a dense crowd of stars in the sky round the circle of the half-moon, a fine night giving them a gentle radiance, but at another time they are scarce, so that we wonder at their flight, when the full moon hides them or when the rays of the sun or the planets above-mentioned dim our sight. But the moon herself also is undoubtedly sensitive to the variations of the strength of impact of the rays of the sun, as moreover the curve of the earth dulls their impact, except when the impact of the rays meets at a right angle. And so the moon is at half in the sun's quadrature, and curved in a hollow circle in its trinal aspect, but waxes to full at the sun's opposition, and then waning exhibits the same configurations at corresponding intervals, on the same principle as the three planets above the sun.

XVII The sun itself has four differences, as there are two equinoxes, in spring and autumn, when it coincides with the centre of the earth at the eighth degree of Aries and Libra, and two changes of its course, in the eighth degree of Capricorn at midwinter when the days begin to lengthen and in the same degree of Cancer at the summer solstice. The variation is due to the slant of the zodiac, as at every moment an equal part of the firmament is above and below the earth; but the planets that follow a straight path at their rising keep their light for a longer tract and those that follow a slanting path pass in a swifter period.

The sun's motions
Reason for inequality of days

Previous chapters: I - VII

Following chapters: XVIII - XXXVIII