[Image:Dew on a flower.jpg|right|220px|thumb|Some dew on an iris
Iris (plant)
Iris is a genus of 260-300species of flowering plants with showy flowers. It takes its name from the Greek word for a rainbow, referring to the wide variety of flower colors found among the many species...

 in Sequoia National Park
Sequoia National Park
Sequoia National Park is a national park in the southern Sierra Nevada east of Visalia, California, in the United States. It was established on September 25, 1890. The park spans . Encompassing a vertical relief of nearly , the park contains among its natural resources the highest point in the...

Dew is water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 in the form of droplets that appears on thin, exposed objects in the morning or evening. As the exposed surface cools by radiating
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....

 its heat, atmospheric moisture condenses
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

 at a rate greater than that at which it can evaporate
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

, resulting in the formation of water droplets.

When temperatures are low enough, dew takes the form of ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

; this form is called frost
Frost is the solid deposition of water vapor from saturated air. It is formed when solid surfaces are cooled to below the dew point of the adjacent air as well as below the freezing point of water. Frost crystals' size differ depending on time and water vapour available. Frost is also usually...

 (frost is, however, not frozen dew).

Because dew is related to the temperature of surfaces, in late summer it is formed most easily on surfaces which are not warmed by conducted heat from deep ground, such as grass, leaves, railings, car roofs, and bridges.

Dew should not be confused with guttation
Guttation is the appearance of drops of xylem sap on the tips or edges of leaves of some vascular plants, such as grasses. Guttation is not to be confused with dew, which condenses from the atmosphere onto the plant surface.- Process :...

, which is the process by which plants release excess water from the tips of their leaves.
Water vapour will condense into droplets depending on the temperature.