Having thus introduced the subject of astronomy by this brief reference to its history, I will now call your attention, first, to the Solar system, and then to the heaven of the fixed stars. THE SOLAR SYSTEM. The SUN is the centre of the Solar system, and never moves from its place. It revolves on its axis in twenty-five days ten hours. The sun is the source of light, heat, and vegetation. The diameter of the sun is 880,000 miles, so that its magnitude is more than a million times greater than the bulk of our earth; and if you could imagine our globe to swell out and reach the moon, it would still have to go 200,000 miles beyond it, ere it occupied a space equal to the sun. The distance of the sun from the earth is upwards of 94,000,000 of miles; and yet so fervent are its rays, that, on a summer's day, when yet it is four hours from the meridian, or noon, we are glad to shelter ourselves from its burning heat. It seems impossible to ascertain what the character of the body of the sun may be. Sir Isaac Newton, and the great French astronomer La Place, imagined it to be a body of fire; but the opinion that now obtains is, that it is an opaque body, surrounded with a fiery atmosphere. Thus they account for the dark specks on its disk. THE PLANETS. Immediately dependent on the sun are the planets, all deriving their light from him. These all revolve round the sun in unequal periods: those within the orbit of the earth, make their annual revolution in less than our year, and those beyond our orbit, in an increased period, according to the extent of their respective orbits. But, to prevent confusion in your minds, I have drawn out a table of the planets,* with their names, distances from the sun, the duration of their annual circuit, and their size as compared with the earth. Some of the planets have moons or satellites, which are called secondary planets; the Earth has one, Jupiter four, Saturn seven, Georgium Sidus six; the motion of these moons is from west to east, excepting those of the last named planet, which are from east to west. The planets whose orbits are within the earth's orbit are called Inferior, aud those without Superior. The planets are preserved in their orbits by the two-fold operation of the centripetal and centrifugal force; the former, as the word implies, ever attracting them to their centre, the sun; the other, ever impelling them from the centre; but let us now view them for a little in their order. Mercury. The heat of this planet, from its nearness to the sun, is very great, above boiling quicksilver; water would boil at its poles; of course, if inhabited, it must be by beings totally dissimilar to man. Venus is by far the most brilliant of all the stars of light, and has been seen in the full day by the naked eye. The heat of Venus, * See Appendix. except at the poles, would be too great for the animal or vegetable life with which we are acquainted. THE EARTH. I have preferred waiting until we reached the orbit of the earth, to explain to you a few particulars concerning it. Here, indeed, we can speak with more certainty, as from the most accurate observations, its size, &c., have been all ascertained. The earth is a dark opaque body, and has no light of its own. It is composed of sea and land, in the proportion of three-fourths water to one-fourth dry land. The earth is about twenty-five thousand miles round; its shape, however, is not a perfect globe, as it is rather flat, like an orange, at the poles; so that if a line were run from the equator through the centre to the other side, it would extend twenty-five miles further than if run through the earth from pole to pole. The earth has two motions, one diurnal, or daily, the other annual, or yearly; by its diurnal motion it revolves on its axis once in twentyfour hours, and this gives the changes of day and night; by its annual motion it performs its circuit in the heavens round the sun, in three hundred and sixty-five days six hours, and this gives the changes of the seasons; and thus it is that the Lord's gracious purposes are fulfilled-seed time and harvest, cold and heat, summer and winter, day and night," fulfil their course. (Gen. viii. 22.) The earth's annual pathway, as she passes on through the heavens, is at the rate of fifty-eight thousand miles an hour, and yet all this while we are not sensible of the least motion whatever; for though we revolve round, as well as hasten on, with this inconceivable velocity, yet we are quite unconscious of it. The sun appears to change its place, but yet is fixed; we appear fixed, and yet are never still.* "In the ordering of these events, we trace the hand of an Almighty Creator, ever watchful over the comforts of the human race. "The inclination of the earth's axis to the orbit which it describes, and its constant direction to the same point in the heavens, viz., the pole, afford us the agreeable changes of summer and winter, spring and autumn. "If the axis of the earth, or the line round which it turns, were perpendicular to its orbit, or, which is the same thing, to the plane in which the sun is, the parts about the equator would be constantly exposed to the full effects of the sun's rays, and be burnt up with intolerable heat: the day and night would be equal all over the globe, and the same season reign perpetually."† Thus, in place of the grateful vicissitudes of the seasons, the earth * This you will see strikingly illustrated on board a ship passing up the river Thames, with a strong flood tide and easterly wind; THERE IS NO PERCEPTIBLE MOTION, the vessel appears fixed, and the land seems approaching, passing, and receding from you, and this is especially the case if you are looking through the cabin windows; and yet the reverse is the real fact. + See a very valuable little Treatise on Astronomy, by the Rev. G. T. Hall.— Parker, Strand. under and near the equator would be parched with burning heat, and countries in our latitude would have ALWAYS a cold and cheerless spring, while a stern unyielding winter would reign in the higher regions of the north; but our God is a God of mercy and of love, and thus it is that every country has its harvest; and though the summer of the north is short, it is blooming and fresh. The earth's atmosphere I have treated of at large in the day of its creation. (Page 19.) THE MOON. This grateful planet, that comes to cheer us through the night, has been the continual theme of poets as well as of astronomers, and this too in all countries; how beautiful is the language of our own Milton: : "Fragrant the fertile earth After soft showers; and sweet the coming on Of grateful evening mild; then silent night Paradise Lost, book iv. Although the moon does not convey to us any heat, but simply reflects from its surface the light of the sun, yet the language of * Journal of a Lapland and Siberian Summer.-" June 23, snow melting; July 1, snow gone; July 9, fields green; July 17, plants full grown; July 25, plants in flower; August 2, fruit ripe; August 18, snow."-Sharon Turner's Sacred History of the World, vol. i. p. 208. |