Popular Astronomy, And, The Orbs of Heaven

INTRODUCTION.

THE great dome of the heavens, filled with a countless multitude of stars, is beyond a doubt the most amazing spectacle revealed by the sense of sight. It has excited the admiration and curiosity of mankind in all ages of the world. The study of the stars is therefore coeval with our race, and hence we find many discoveries in the heavens of whose origin neither history nor tradition can give any account. The science of Astronomy, embracing, as it does, all the phenomena of the celestial orbs, has furnished in all ages the grandest problems for the exercise of human genius. In the primitive ages its advances were slow; but by patient watching, and by diligent and faithful records transmitted to posterity from generation to generation, the mysteries which fill the heavens were one by one mastered, until at length, in our own age, there remains no phenomenon of motion unexplained, while the distances, magnitudes, masses, reciprocal influences, and physical constitution of the celestial orbs have been approximately revealed. In a former volume an attempt was made to trace the career of discovery among the stars, and to exhibit the successive steps by which the genius of man finally reached the solution of the great problem of the universe.

The performance of that task did not permit the special study of any one object, except so far as it was required in the march of the general investigation. It is our object now to execute what was then promised, and to examine in detail the various bodies which are allied to the sun, constituting (as we shall find) a delicately-organized system of

The Orbs of Heaven."

revolving worlds, a complex mechanical structure, whose stability has challenged the admiration of all thinking minds, and whose organization has furnished the most profound themes of human investigation.

The plan adopted will lead us to present clearly all the facts and phenomena resulting from observation; with these facts the student may exercise his own genius in attempting to account for the phenomena, before proceeding to accept the explanation laid down in the text.

To aid the memory, and to present a systematic investigation, we shall adopt the simple order of distance from the solar orb, commencing with that grand central luminary, and proceeding outward from planet to planet, until we shall develop all the phenomena employed in the discovery of the great law of universal gravitation. With a knowledge of this law the worlds already examined cease to be isolated, and arrange themselves, under the empire of gravitation, into a complex system, the delicate relations of whose parts leads to a new discovery and to the final perfection of the system of solar satellites.

Having closed our investigation of the planets and their tributary worlds, we shall render an account of those anomalous bodies called comets, which, by the suddenness of their appearance, their rapid and eccentric motions, and the brilliant trains of light which sometimes attend them, have excited universal interest, not unattended with alarm, in all ages of the world.

Before passing to the execution of this plan, we must examine, to some extent, the phenomena of the nocturnal heavens, as the stars furnish the fixed points to which all moving bodies are referred.

To the eye the heavens rise as a mighty dome, a vast hollow hemisphere, on whose internal surface the glittering stars remain for ever fixed. In case we watch through an entire night, we find the groupings of stars slowly rising from the east, gradually reaching their culmination, and then gently sinking in the west. A more attentive exami

nation enables the eye to detect some of these groups of stars towards the north which ever remain visible, rising, culminating, and descending, but never sinking below the horizon. Every star in this diurnal revolution, as it is called, is found to describe a circle, precisely as if the concave heavens were a hollow sphere to which the stars were attached, and that this hollow globe were made to revolve about a fixed axis, passing through its centre. Indeed, we find by attentively watching, that this hypothesis of a spherical heavens, accounts for all the phenomena already presented. As the stars are situated nearer to the extremity of the axis of revolution, the circles they describe grow smaller and smaller, until, finally, we find one star which remains fixed; and this one must be at the point where the axis of the heavens pierces the celestial sphere. This is called the north star; and the point in which the axis pierces the heavens is called the north pole. The opposite point is called the south pole.

Only one half of the celestial sphere is visible at one time above the horizon; but this spherical surface extends beneath the horizon, and forms a complete sphere, encompassing us on all sides, while its centre seems to be occupied by the earth. It is true that, in the daytime, the stars fade from the sight in the solar blaze; but they are not lost; they still fill the heavens, as we shall see hereafter, and the starry sphere sweeps unbroken entirely round the earth.

These great truths, the diurnal revolution of the heavens, its spherical form, the central position of the earth, the north polar star, the axis of the heavens, the circles described by the stars, were among the discoveries of primitive antiquity, and are matters of the most simple observation.

The spherical form of the heavens was soon imitated, and the artificial globe became one of the first astronomical instruments. On this artificial globe certain lines were drawn to imitate those described in the heavens by the celestial orbs; and as these lines must henceforth form a part of our language, we proceed to give the following Definitions :—

A great circle is one whose plane passes through the centre of the sphere.

A small circle is one whose plane does not pass through the centre of the sphere.

The axis of the heavens is an imaginary line passing through the centre of the earth, and about which the heavens appear to revolve once in twenty-four hours.

A meridian is a great circle passing through the highest point of the celestial sphere (called the zenith) and the axis of the heavens.

The equator or equinoctial is a great circle, perpendicular to the axis of the heavens, and half-way between the north and south polar points.

These important lines have been employed from the earliest ages in the study of the heavenly bodies; and having thoroughly mastered their meaning and position, we are prepared to examine any changes of location which may be discovered among the vast multitude of shining bodies which go to fill up the concave of the celestial sphere.

We shall proceed, then, without further delay, to the execution of the plan already laid down.

« Anterior Continuar »

Libros