238 GEOGRAPHY ANY) ASTRONOMY. star.* But I think it is easier for a learner to find a star's place by its declination, and right ascension; and the common astro- nomical problems seem to be solved more naturally and easily by thismethod. It may be here mentioned, though it is before its proper place, that the several planets, viz. Saturn, Jupiter, Mars, Venus, Mercury, and the Moon, make their revolutions at very different distances from the earth, from the sun, and from one another; each having its distinct orbit or path nearer or farther from us. And as eachof their orbits is at vastly different dis- tances, so neither are they perfectly parallel to one another, nor to theecliptic or yearly path of the sun. Thence it follows that these planets have some more, some less latitude, because their orbits or paths differ some few de- grees from the sun's path, and intersect or cross the ecliptic, at two opposite points in certain small angles of two, three, four or five degrees, which points are called the nodes. The node where any planet crosses the ecliptic ascend- ing to the northward is called the dragon's head, and marked thus Where the planet crosses the ecliptic descending to the southward, it is called the dragon's tail and marked thus. It is very difficult to represent the latitude of the planets in their different orbits either upon a globe, or Upon a flat or plain surface ; the best way that I know is, to take two small hoops of different sizes, as in figure xi. and thrust a straight wire c o through them both in the two opposite parts of their circumfer- ence : Then turn the innermost hoop (which may represent the path of the moon) so far aside or obliquely as to make an angle of 5, degrees with the outermost hoop, (which represents the stet's path.) Thus the two points e and o or a and S¡, where the wire joins the hoops, are the two nodes or the points of inter- section. This difference of orbits of the planets and their intersec- tions, or nodes, may be represented also by two circular pieces of pasteboard as in figure xii. When the less (whose edge re- presents the moon's orbit,) is put half way through a slit A, B, that is made in the diameter of the larger (or the sun's orbit, and then brought up smear to a parallel or level with the larger within 5f degrees. Thus the two nodes will be represented by A and B. , t Astronomers know that notonly the 12 constellations of the zodiac, bat also all thefixed stars seem to move from the west toward toe cast about 50' in a year, or one degree in '12 years, in circles parallel to the ecliptic. Therefore their declination is a little altered in '12 years time, that being measured from the equator : But their latitude never alters, that being measured from the ecliptic And upon this account astronomers use the latitude rather than the declination in their measures, because it abides the same for ever.
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