Equinox

(ē'kwe-noks.) [From L. æquus, equal, and nox, night.] (Ast.) The period when the sun cro es the celestial equator. His pa age from S. to N. of the equator, which occurs on about the 21st of March, marks the period of the vernal E.; his pa age from N. to S. of the equator, which occurs on about the 23d of Sept., marks the period of the autumnal E. Owing to the ellipticity of the earth's orbit, the interval between the vernal and the next autumnal E. is nearly 8 days greater than the interval between the autumnal and the next vernal E.; for the earth pa es her perihelion in mid-winter, and then moves most swiftly in her orbit,whereas in mid-summer she pa es her aphelion, and moves most slowly. It is nece ary to remark that for the southern hemisphere the vernal and antumnal equinoxes are interchanged; and the southern summer is, of course, shorter than the southern winter. 22 2S [s. 337]