White Dew白露

White Dew (白露, Bái Lù) is the fifteenth of the twenty-four solar terms and the month-opener that follows End of Heat. It is an astronomical instant, not a day: the moment the sun reaches 165° of ecliptic longitude, which falls somewhere between 7 and 9 September depending on the year.

The name describes a visible sign rather than an abstraction: nights are now cool enough, against days still warm, that moisture in the air condenses into dew by morning — pale enough in early light to read as "white". It is one of the more literally observational names among the twenty-four.

It sits between End of Heat and the Autumn Equinox, roughly two weeks out from each, in the stretch where autumn stops being a name on the calendar and starts being something felt in the morning air. In the agricultural calendar it marks a turning point for many autumn crops, where the day–night temperature swing itself becomes part of what ripens them.

White Dew is a 節 — a month-opening term — so at the instant the sun crosses 165° the month pillar's branch becomes 酉 (Yǒu). This is the term that puts 酉 in place for anyone born from this instant forward until the next 節, Cold Dew, arrives roughly a month later.

This site's calculator applies that rule at the astronomical instant, not on a fixed calendar date: a birth in the days around 7–9 September can carry either 申 (from Beginning of Autumn, the previous 節) or 酉, depending on which side of the crossing the birth time falls.

Cold Dew (寒露) — The twenty-four solar terms. The next month-opener after this one, roughly a month later, and easy to mix up because both names are built the same way — a temperature word plus "dew". Both are 節: White Dew opens the 酉 month pillar and Cold Dew opens 戌, so getting them backwards means getting the month pillar wrong, not just the label.