morning dew
The morning dew is the occurrence of dew in the morning and consists of precipitation of very fine water droplets on the surface and on plants. It is formed from the water vapor contained in the air close to the ground , which condenses as a result of the nightly cooling . If the weather is uniform, this cooling begins around 3 p.m. the previous day and increases most strongly in the first hours of the night (up to 2 ° C per hour when the sky is clear). The temperature minimum, however, only occurs shortly before sunrise, so that dew formation continues until then.
In principle, dew can occur at any time of the day, but is usually perceived as fog during the day . The morning dew, on the other hand, often accompanies the fact that the possible fog only reaches a height of a few centimeters (visible over meadows when viewed from the ground) to a maximum of one or two meters - which is why it is called morning fog. In autumn it can reach a height of almost 2 kilometers as high fog (see peplopause ), but then it usually arises around midnight.
For the flora and fauna in the desert and other arid areas, the morning mist has the important function of a fairly regular supply of humidity . Numerous plants close to the ground can only survive through the occasional or regular morning dew, and some species of beetles catch the dew droplets on their antennae, legs and the chitin armor.
During survival training in the desert you learn, among other things, to collect the dew with tarpaulins or other aids to replenish the supply of drinking water. The process is usually most effective at dawn .
For astronomy, the dew - and especially the morning dew - is often a difficult problem. If the lenses or mirrors fog up even a little, the transparency and image contrast decrease sharply. With small telescopes you can use a dew cap , with larger telescopes with very weak electrical heating of the inlet opening. However, it can cause thermal bending of the telescope or increase the refraction of the hall if the observatory domes are only partially open .