The great path of the Sun among the constellations as seen from the Earth is called the Ecliptic. It is divided into 360°, and again into twelve equal parts of 30°, called Signs. As one half of the ecliptic is north, and the other half south, of the equator, the line of intersection of their planes is at two points which are known as the equinoctial points, because, when the Sun on his upward and downward journey arrives at either of them the days and nights are of equal length all over the world. The equinoctial points are not stationary, but have a westerly motion of 50'' annually along the ecliptic; at this rate they will require a period of 25,868 years to complete an entire circuit of the heavens.

Milton alludes to the ecliptic when he mentions the arrival of Satan upon the Earth:—

Extending for 9° on each side of the ecliptic is a zone or belt called the Zodiac, the mesial line of which is occupied by the Sun, and within this space the principal planets perform their annual revolutions. It was for long believed that the paths of all the planets lay within the zodiac, but on the discovery of the minor planets, Ceres, Pallas, and Juno, it was ascertained that they travelled beyond this zone. The stars situated within the zodiac are divided into twelve groups or constellations, which correspond with the twelve signs, and each is named after an animal or some figure which it is supposed to resemble. The zodiac is of great antiquity; the ancient Egyptians and Hindoos made use of it, and there are allusions to it in the earliest astronomical records. The twelve constellations of the zodiac bear the following names:—

In close association with the Sun’s annual journey are the seasons, upon the regular sequence of which mankind depend for the various products of the soil essential for the maintenance and enjoyment of life. The revolution of the Earth in her orbit, and the inclination of her axis to her annual path, causing the plane of the equator to be inclined 23½° to that of the ecliptic, are the reasons which account for the succession of the seasons—Spring, Summer, Autumn, and Winter. Owing to the position of the Earth’s axis with regard to her orbit, the Sun appears to travel 23½° north and 23½° south of the equator. When, on June 21, the orb attains his highest northern altitude, we have the summer solstice and the longest days; when, by retracing his steps, he declines 23½° below the equator, at which point he arrives on December 21, we have the winter solstice and the shortest days. Intermediate between those two seasons are spring and autumn. When the Sun, on his journey northward, reaches the equator, we have the vernal equinox, and at this period of the year the days and nights are of equal length all over the globe. In a similar manner, when, on his return journey, the Sun is again on the equator, the autumnal equinox occurs. In summer the North Pole is inclined towards the Sun, consequently his rays fall more direct and impart much more heat to the northern hemisphere than in winter, when the Pole is turned away from the Sun. This difference in the incidence of the solar rays upon the surface of the globe, along with the increased length of the day, mainly accounts for the high temperature of summer as compared with that of winter.

Astronomically, the seasons commence at the periods of the equinoxes and solstices. Spring begins on March 21, the time of the vernal equinox; summer on June 21, at the summer solstice; autumn on September 22, at the autumnal equinox; and winter on December 21, at the winter solstice. This conventional division of the year is not equally applicable to all parts of the globe. In the arctic and antarctic regions spring and autumn are very brief, the summer is short and the winter of long duration. In the tropics, owing to the comparatively slight difference in the obliquity of the Sun’s rays, one season is, as regards temperature, not much different from the other; but in the temperate regions of the Earth the vicissitudes of the seasons are more perceptible and can be best distinguished by the growth of vegetation, and the changes observable in the foliage of shrubs and trees. In spring there is the budding, in summer the blossom, in autumn the fruit-bearing, and in winter the leafless condition of deciduous trees, and the repose of vegetable life.

The legendary belief that before the Fall there reigned on the Earth a perpetual spring, is introduced by Milton in his poem when he describes the pleasant surroundings associated with the happy conditions of life that existed in Paradise:—

In sad contrast with this charming sylvan scene, we turn to the unhappy consequences which ensued as a result of the first act of transgression. Milton describes a change of climate characterised by extremes of heat and cold which succeeded the perpetual spring. The Sun was made to shine so that the Earth should be exposed to torrid heat and icy cold unpleasant to endure. The pale Moon and the planets were given power to combine with noxious effect, and the fixed stars to shed their malignant influences:—

We are here afforded an opportunity of learning that Milton possessed some knowledge of astrology, to which he makes allusion in other parts of his poem besides. In his time, astrology was believed in by many persons, and there were few learned men but who knew something of that occult science. Milton may be included among those who devoted some attention to astrology. Of this there is ample evidence, by the manner in which he expresses himself in words and phrases in common use among astrologers.

The professors of this art recognised five planetary aspects, viz., opposition, conjunction, sextile, square, and trine, each possessing its peculiar kind of influence on events. The Moon, the planets, and the constellations in their conjunctions and configurations, were believed to reveal to those who could understand the significance of their aspects, the destiny of individuals and the occurrence of future events. The inauspicious influences of the heavenly bodies are described by Milton as contributing to the general disarrangement of the happy condition of things that existed before the Fall.

After having described the adverse physical changes which occurred in Nature as a consequence of the Fall, Milton makes use of his astronomical knowledge in explaining how they were brought about, and suggests two hypotheses: (1) a change of position of the Earth’s axis; (2) an alteration of the Sun’s path from the equinoctial road:—

In support of the theory of a perpetual spring, Milton assumes that the Earth’s axis was directed at right angles to her orbit, and that the plane of the equator coincided with that of the ecliptic. Consequently, the Sun’s path remained always on the equator, where his rays were vertical, and north and south of this line each locality on the Earth enjoyed one constant season, the character of which depended upon its geographical position. In what are now the temperate regions of the globe there was one continuous season, similar in climate and length of day to what is experienced at the vernal equinox, when the Sun is for a few days on the equator. There was then no winter, no summer, nor autumn; and, consequently, the growth of vegetation must have taken place under conditions of climate entirely different to what exist on the Earth at the present time.

The change of position of the Earth’s axis, ‘twice ten degrees and more from the Sun’s axle,’ is described by Milton as having been accomplished by the might of angels, who ‘with labour pushed oblique the centric globe.’

(2) According to the Ptolemaic belief, the Sun revolved round the Earth, but his course was altered from the equinoctial road to the path that he now pursues, which is the ecliptic. Instead of remaining on the equator, he travels an equal distance from this line upwards and downwards in each hemisphere.

The path of the Sun in the heavens is described by Milton with marked precision, and he mentions in regular order the names of the zodiacal constellations through which the orb travels. Passing through Taurus with the seven Atlantic Sisters (the Pleiades) and the Spartan Twins (Gemini), he enters the Tropic Crab (Cancer), in which constellation he attains his highest northern altitude; thence downwards he travels through Leo, Virgo, and the Scales (Libra), as deep as Capricornus, reaching his lowest point of declination at the winter solstice; and were it not for this alteration of the Sun’s path, the poet informs us that perpetual spring would have reigned upon the Earth.

Milton was evidently well acquainted with the astronomical reasons (the revolution of the Earth in her orbit and the obliquity of the ecliptic) by which the occurrence and regular sequence of the seasons can be explained.

The path of the Sun in the heavens; his upward and downward course from the equator; the names of the constellations through which the orb travels, and the periods of the year at which he enters them, were also familiar to him.

The grateful change of the seasons, and the varied aspects of nature peculiar to each, which give a charm and freshness to the rolling year, must have been to Milton a source of pleasure and delight, and have stimulated his poetic fancy.

His observation of natural phenomena, and his keen perception of the pleasing changes which accompany them, are described in the following lines:—

The ancient poets Virgil and Ovid describe the Earth as having been created in the spring; and associated with this season, which

were the Graces and the Hours, which danced hand in hand as they led on the eternal Spring.

Milton alludes to the seasons on several occasions throughout his poem, and to the natural phenomena associated with them:—

The Sun is in the constellation Taurus in April, when the warmth of his rays begins to impart new life and activity to the insect world after their long winter’s sleep.

In his description of the repast partaken by the Angel Raphael with Adam and Eve in Paradise, Milton writes:—

In describing Beelzebub when about to address the Stygian Council, he says:—

The failing vision from which Milton suffered in his declining years was succeeded by total blindness. This sad affliction he alludes to in the following lines:—

We are able to perceive how much Milton was impressed with the beautiful seasons, and the varying aspects of the year which accompany them, and how his poetic imagination luxuriated in the changing variety of nature observable in earth and sky that from day to day afforded him exquisite delight; and, although his poem was written when blindness had overtaken him, yet those glad remembrances remained as fresh in his memory as when in his youth he roamed among the flowery meadows, the vocal woodlands, and the winding lanes of Buckinghamshire.

The idea expressed by Milton that the primitive earth enjoyed a perpetual spring, though pleasing to the imagination, and well adapted for poetic description, is not sustained by any astronomical testimony. Indeed, the position of the Earth, with her axis at right angles to her orbit, is one which may be regarded as being ill adapted for the support and maintenance of life on her surface, just as her present position is the best that can be imagined for fulfilling this purpose.

Astronomy teaches us to rely with certainty upon the permanence and regular sequence of the seasons. The position of the Earth’s axis as she speeds along in her orbit through the unresisting ether remains unchanged, and her rapid rotation has the effect of increasing its stability. Yet, the Earth performs none of her motions with rigid precision, and there is a very slow alteration of the position of her axis occurring, which, if unchecked, would eventually produce a coincidence of the equator and the ecliptic. Instead of a succession of the seasons, there would then be perpetual spring upon the Earth, and, although it would require a great epoch of time to bring about such a change, there would result a condition of things entirely different to what now exists on the globe. But, before the ecliptic can have approached sufficiently near the equator to produce any appreciable effect upon the climate of the Earth, its motion must cease, and after remaining stationary for a time, it will begin to recede to its former position. The seasons must therefore follow each other in regular sequence, and throughout all time, reminding us of the promise of the Creator, ‘that while the Earth remaineth seed-time and harvest, and cold and heat, and summer and winter shall not cease.’