the sixth magnitude; elements of Herschel; six satellites attend this planet; To a spectator at the sun the planets would appear to move in harmonious order from west to east; he would probably take the period of Mercury as a standard for comparing the periods of planets; the paths of the planets would Prospect at Mercury; all the planets would appear to have conjunctions and oppositions; their motions would seem sometimes direct, sometimes retrograde. Prospect at the Earth; the inferior planets exhibit conjunctions, but no op positions; the superior conjunctions and oppositions in succession; appear- ance of looped curves not compatible with our organ's of vision. Prospect at Herschel; Saturn the only planet visible to its inhabitants; there may be other planets, unknown to us, but well known to the inhabitants of the Causes of planetary motion. Projectile, centrifugal and centripetal forces defined; matter is in itself inac- tive; a body impelled by one force always moves in a right line; circular and elliptical motion how caused; the planets move in ellipses; the larger the or- bits of the planets are, the greater must the projectile force be in proportion Time measured by the sun differs from that of a good clock or watch; the Shows the benevolence of the Deity; the harvest moon caused by the posi- through the same signs in each revolution, but the equal rising is not perceived Kepler first discovered the cause of the tides; simply the attraction of the heavenly bodies does not cause the tides, but the unequal attraction; the tide on the side of the earth opposite to the moon how caused; the poles can have but two tides in a revolution of the moon round the earth; single tides in some places; the tide not on the meridian till after the moon has passed; the sun attracts the earth more than the moon, but raises a less tide on account of his great distance; spring and neap tides; when the highest tides of all hap- pen; lakes and small seas have no tides; Mr. Ferguson's judicious remark Planets shining by the sun's light cast shadows on the side opposite to the sun; eclipses can happen but between a primary planet and its own secondaries; how the extent of the earth's shadow may be found; the obliquity of the moon's orbit to the ecliptic prevents eclipses, except when the syzygies are near the nodes; eclipses of the moon partial, total, and central; why the moon is visi- ble, when totally eclipsed; the dark shadow of the moon how extensive; eclipses of the sun sometimes annular; the penumbra, the line of the moon's nodes, moves backwards; eclipses return at the same node after 223 mean lu- nations, in a period of a little more than 18 years; when a series of eclipses has closed at the earth, how long before a new series will begin; notice of the memorable eclipse in June 16, 1806; extent of the moon's dark shadow on the earth; how this extent may be found; extent of the penumbra on the earth, and how found; duration of total darkness in a solar eclipse, and how such duration may be found; greatest duration of a general eclipse on the earth, and mean duration of the same; when the general eclipse begins and ends; position of the earth's axis affects solar eclipses; catalogue of visible eclipses. To calculate new or full moon for any time in the 19th century; to calcu- late the time of new or full moon in any year of the christian era before the 19th century; to calculate the time of new or full moon in any year before the christian era; to calculate the time of new or full moon in any year after To calculate the true place of the sun at any time in the 19th century; in the christian era, before the 19th century; before the christian era; after the 19th century; to calculate the true distance of the sun from the moon's ascending Projection of lunar eclipses; elements; projection of the lunar eclipse in Periods, cycles, epact, Roman Indiction; year Julian and Gregorian; al- teration of style; months; days; when begun by different nations; nautical and astronomical day; parts of a day; dominical letter; table of dominical letters; how to find on what day of the week any month begins. Is diminishing; diminution caused by the attraction of the moon. Diurnal parallax of the moon; how it may be taken by one observation; Parallax of the sun; method proposed by Aristarchus for finding this par- How they were formerly considered; their appearance; opinions of dif- tion. Astronomers consider them suns to other systems; their stationary appear- the naked eye; binary stars; stars are classed according to their magnitude; Atmospheric refraction; increases the length of the day; causes the disk of the sun or moon to appear elliptical near the horizon; table of refraction. The latitude of a place may be determined by the distance of its zenith from the celestial equator; it may be determined by the altitude of its elevated Entroduction. ASTRONOMY is the science, which treats of the heavenly bodies. The term is compounded of two Greek words, signifying the law of the stars, or constellations. It is a science of great antiquity, and one of the most useful and sublime, that can employ the contemplation of man. By it are known the figure and magnitude of the earth, and the situation and distance of places the most remote. By it is investigated the cause of inequality in the seasons, the changes of day and night, with all the pleasing variety, afforded by those phenomena. The mariner is dependant on this science for his only sure guide on the trackless ocean. But, above all, Astronomy affords the most enlarged view of the Creator's works. The astronomer seems to open his eyes in a vast and unknown expanse. He beholds the stars, which bespangle and beautify our canopy, magnified into so many suns; surrounded with worlds of unknown extent, constituting systems, multiplied beyond the utmost bound of human imagination, and measured only by the omnipresence of Jehovah; all moving in perfect harmony, in subjection to his omnipotent controul. DIFFERENT SYSTEMS OF ASTRONOMY. The learned have formed different hypotheses respecting the position and movement of the great heavenly luminaries. |