. Astronomy for high schools and colleges . path of the sun lay inthe equator, it would, during the entire year, rise exactlyin the east and set in the west, and would always crossthe meridian at the same altitude. The days wouldalways be twelve hours long, for the same reason that astar in the equator is always twelve hours above the hori-zon and twelve hours below it. But we know that tliisis not the case, the sun being sometimes north of theequator and sometimes south of it, and therefore havinga motion in declination. To understand this motion, 102 ASTMOKOMT. suppose that on March 19th, 18
. Astronomy for high schools and colleges . path of the sun lay inthe equator, it would, during the entire year, rise exactlyin the east and set in the west, and would always crossthe meridian at the same altitude. The days wouldalways be twelve hours long, for the same reason that astar in the equator is always twelve hours above the hori-zon and twelve hours below it. But we know that tliisis not the case, the sun being sometimes north of theequator and sometimes south of it, and therefore havinga motion in declination. To understand this motion, 102 ASTMOKOMT. suppose that on March 19th, 18Y9, the sun had beenobserved with a meridian circle and a sidereal clock at themoment of transit over the meridian of Washington. Itsposition would have been found to be this : Eight Ascension, 23^ 55^ 23^; Declination, 0° 30 south. Had the observation been repeated on the 20th andfollowing days, the results would have been : March 20, E. Ascen. 23^ 59^ 2«; Dec.^O° 6 , 0*^ 2°^ 40^; 0° lY North. 22, Qh gm 198. « 0° 41 I^ Fig. 44.—the sun crossing the equator. If we lay these positions down on a chart, we shall findthem to be as in Fig. 44, the centre of the sun beingsouth of the equator in the first two positions, and northof it in the last two. Joining the successive positions bya line, we shall have a small portion of the apparent pathof the sun on the celestial sphere, or, in other words, asmall part of the ecliptic. It is clear from the observations and the figure that thesun crossed the equator between six and seven oclock onthe afternoon of March 20th, and therefore that the equa-tor and ecliptic intersect at the point where the sun was atthat hour. This point is called the vernal equinox^ the THE SUNS APPARENT PATH, 103 wliile the second first word indicating the season,expresses the equahty of thenights and days which occurswhen the sun is on the will be remembered that thisequinox is the point from whichright ascensions are counted inth
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