ELEMENTS OF ASTRONOMY.

INTRODUCTION.

OF THE OBJECT AND USE OF ASTRONOMY.

ASTRONOMY is that science which treats of the heavenly bodies, describing their motions, explaining their appearances, and ascertaining their magnitudes, distances, and relative situation. The name is derived from two Greek words, aoтpor and νομός, which signify the law of the heavenly bodies.

In point both of interest and usefulness, Astronomy may fairly challenge competition with any of the sciences. It is interesting from the very grandeur of the objects to which it relates, and from the sublime views which it unfolds of the vastness and magnificence of the universe. And even if it served no other purpose than the gratification of a liberal curiosity, it would on this ground alone well deserve our attention; for what person, imbued with the smallest love of knowledge, and worthy of the title of a rational being, can willingly remain in ignorance of the causes which operate in producing those grand changes and move

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ments of nature, so important to the welfare of the human race the alternations of day and night, and the beautiful and grateful succession of the seasons? Who can regard with unadmiring and uninquisitive view the sublime spectacle of the nocturnal heavens; the devious courses of the planets; the changeful aspect of the moon; or the insufferable splendour of the orb of day,

"Best image here below

Of its Creator, ever pouring wide,

From world to world, the vital ocean round?” ·

Dull indeed must that mind be, and dead to all the charms of knowledge, which does not burn with eager curiosity to learn whatever may be known respecting these great objects. If, however, purposes of more substantial utility be sought for, Astronomy is by no means wanting in this recommendation; for it has materially contributed to the improvement of some of the most important arts of life, and has a close connexion with many unquestionably useful branches of knowledge. By its aid the navigator directs his course through the trackless ocean, and commerce, thus extended to the remotest regions of the globe, enriches us with the productions of every clime, and forms a bond of alliance, to their mutual advantage, between nations which would otherwise have been ignorant of each other's existence. By its assistance the earth has been measured, and the geographer is furnished with an unerring method of ascertaining the exact

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situation and extent of the countries which he delineates or describes. It furnishes the only certain and invariable standard for the computation of time, and history is indebted to it for the recovery of many important dates, which the imperfect annals of remote antiquity had left uncertain. Nor should it be forgotten, that the light of Astronomy has utterly dispelled those groundless terrors which the more extraordinary phænomena of the heavens were formerly wont to inspire; and comets and eclipses are now no longer looked upon, except among barbarous and unenlightened nations, as tokens of divine anger, or harbingers of war and pestilence. The same cause has also contributed to bring into deserved discredit that vain science which pretended to read the destinies of man in the aspects of the planets. But of all the uses and advantages of Astronomy, the highest and most important, and that which strongly recommends it to the attention of all without exception, consists in the striking evidence which it affords of the existence and perfections of the Great Supreme. The grand spectacle of the heavens has ever been considered as presenting the most powerful impulse to rational devotion, and the most striking lesson of natural religion. It is here that we discover the highest wonders of creation, and observe the clearest display of that admirable order and contrivance which so plainly evince the superintendence of a great designing Cause. "The heavens," said the Psalmist, "declare the glory of God, and the firmament showeth his handy-work:" and who that

has once held converse with the skies, but will feel the full truth and force of the pious sentiment? So clear, indeed, is the evidence which this science affords of the existence and attributes of God, and so just and enlarged the ideas which it suggests of his character, that I can hardly consider it as any exaggeration to assert, in the words of the poet, that

"An undevout Astronomer is mad."

Young's Night Thoughts.

CHAPTER I.

DESCRIPTION OF THE MORE OBVIOUS APPEARANCES. OF THE HEAVENS.

THE first step in the study of Astronomy is to observe the general aspect and more obvious appearances of the heavens, and then to consider how these appearances may be accounted for. The student of this science, instead of entering at once into those grand views of the structure of the universe which have been unfolded by modern discoveries, should endeavour to place himself, as much as possible, in the situation of the first observers of the heavens, and consider what

facts they had upon which to reason, and what it was that they ascertained or conjectured.

On turning our attention to the heavens, we find ourselves placed in the centre of what appears a vast dome or concave, bending over a plane of unlimited extent. By night this dome or concave appears beautifully studded with countless specks of light, and though they disappear at the approach of the great luminary of day, yet from their gradual disappearance and gradual reappearance, it is readily and naturally inferred that they would be always visible, were it not for the brighter splendour which overpowers their feeble ray. Nor is it much less obvious, after a little