equinox
/ˈi:kwɪnɔks, alsoˈek-; `ikwəˌnɑks, ɛk-/ n
either of the two times in the year (around 21 March and 22 September) when the sun crosses the equator and day and night are of equal length 春分; 秋分
spring/vernal equinox 春分
autumnal equinox 秋分. Cf 参看 solstice.