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vernal equinox; spring equinox
春分の日は昼と夜の長さがほぼ等しい。
On the vernal equinox, day and night are roughly equal.
春分を過ぎると桜の季節が始まる。
After the vernal equinox, cherry blossom season begins.
春分は毎年三月二十日頃に訪れる。
The vernal equinox arrives around March 20 every year.