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representing the season for hunting ; another, the Virgin, a reaper of corn, theseason of the corn harvest; and so on. The zodiac, then, is to be consideredan imaginary belt, or circle, round the starry heavens surrounding us ; andsupposing this circle to be divided into 360 degrees, each of the twelve partsof the zodiac will contain thirty degrees of the entire circle. The zodiac, in itsbreadth, takes in a band, or belt, of stars of sixteen degrees ; eight degreesbroad on each side of the line which marks the apparent path of the sun,because in that width are comprehended the paths, or orbits, of the planets.
Along the middle of this belt of sixteen degrees in breadth, therefore, liesthat circle which, to us, appears to be a path described by the sun in his pro-gress about the earth. But, if we were stationed at the sun, it would be thepath which the earth would appear to describe in its annual motion round thesun; it would appear to be what it really is. This circle, the apparent pathof the sun, but real path of the earth, is called the ecliptic.
It will be understood that, as the sun, in its apparent motion round theearth, seems to arrive at the same point, or star, at the beginning of every year,and at another star at the beginning of every month (with a slight deviation),the astronomer is enabled, by subdividing this great circle into degrees, minutes,and seconds, accurately to describe its apparent periodical motion ; and thus,knowing the point at which the sun will seem to arrive at each day, hour, andeven minute and second, he is enabled to calculate with certainty the precisemotion of the earth—the exact orbit in which it moves ; for, in fact, the samecircle will appear to be described, whether the motion be in the sun, or in theearth. The ecliptic among the stars, and the earth's orbit around the sun, there-fore, are on the same plane; for, with respect both to the sun and the earth,each, as seen from the other, appears to describe the circle called the ecliptic ;seen from the earth, it is called the apparent path of the sun; seen from thesun, it is the apparent path, or orbit, of the earth.
It is important to a distinct apprehension of the uses of the grouping of thestars into constellations, and more especially of those which compose the zodiac,that the orbit of the earth and the ecliptic should be understood to be on thesame plane ; shewing, that the earth’s motion in her orbit is intimately connectedwith the zodiac and its divisions, which belong to the ecliptic.
All that region of the heavens, which is on the northern or upper side of thezodiac, was divided by the ancients into twenty-one constellations, each ofwhich is composed of many stars; and that region which is on the lower, orsouthern side of the zodiac, was divided into fifteen constellations : so that thestars of the whole sphere, including the twelve constellations of the zodiac,were, by them, arranged into forty-eight constellations. Certain stars, however,whose appearance made them of less importance, or whose relative positionsrendered it difficult to include them in any of these constellations, were omittedin this arrangement. Of these, new constellations have been formed, from timeto time, by succeeding astronomers ; and now the whole extent of the heavensis arranged into 108 constellations, containing nearly 4000 stars.