Recently, it has been quite hard to use the telescopes, as leaving them out for a while as the temperature drops causes dew to form over them. But what is dew?
Dew is water that appears on exposed objects in the form of droplets, due to condensation. This process occurs when a material changes from a gas to a liquid, and dew is the result of water changing from a vapour to a liquid.
As the exposed surface radiates its heat and cools, atmospheric moisture
condenses at a greater rate than it can evaporate, as cold air can hold less water vapour than warm air. Humid locations, such as coasts, are more idly to experience dew that arid areas. The temperature at which droplets form is called the dew point, and when the surface temperature reaches this point, atmospheric water vapour condenses.
Dew forms best when there are clear skies, light wind, decent soil moisture and a low night dew point depression, which is the difference between temperature & dew point. Dew forms when the temperature is at the dew point, which usually happens first at ground level, because longwave emission (radiant/thermal energy) causes the earth's surface to cool at night and the soil is often the moisture source for the dew. The cooling of warm moist soil at night causes condensation. Clear skies allow for the maximum release of Iongwave radiation to space, whereas cloudy skin reflect & absorb while re-emitting longwave radiation back to the surface, preventing as much cooling from occurring. Soil moisture is critical to dew formation (especially heavy dew).
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