Why does dew form at night?

Question

... yeah :)

Answer 1

The important condition for the formaton of dew is that the earth's surface should cool down rapidly to reach the dew point temperature which can happen only in the night or early morning.

Answer 2

warm humid air of the day cools down, the moisture in the air condenses and gives us dew on objects.

Answer 3

Dew (or frost) forms on surfaces at night when the surface cools to the dew (or frost) point (the temperature at which saturation occurs).  This is helped by evaporation of water from the surface (soil, grass), adding to the moisture in the air.  Normally you get dew/frost on a night without clouds, as radiational cooling of the Earth's surface increases the rate of cooling.  Since there usually isn't much wind at night, this allows moisture from the surface to build up near the surface, enhancing the effect. If there is wind, the moisture is removed from the vicinity of the surface and dew will not form.

Dew forms when condensation is faster than evaporation.This happens when the earth's surface lose more energy by infrared radiation than it receives though the incident solar radiation which is the case on clear nights.

After the Sun rises, the surface and the air are warmed, raising the temperature and causing the dew to evaporate.  Thus we normally only see dew in the morning.