白露 is the 15th of the 24 solar terms (节气 jiéqi), marking the time around Sept 8-22 when nighttime cooling produces visible dew on grass. The name literally means 'white dew' — old Chinese cosmology assigned the color white to autumn.
history
The poet 杜甫 (Dù Fǔ) wrote the famous line 露从今夜白 ('the dew turns white from this very night') in 月夜忆舍弟 — playing directly on the term 白露 to evoke autumn loneliness.
