RAF ALCONBURY, United Kingdom – Trees, bushes and grass around RAF Alconbury is covered in frost, called hoar frost, Dec. 12. Hoar frost (also called radiation frost, hoarfrost or pruina) refers to the white ice crystals, loosely deposited on the ground or exposed objects, which form on cold clear nights when heat losses into the open skies cause objects to become colder than the surrounding air. The frost itself will be at or below the freezing temperature of water. The name hoar comes from an Old English adjective for showing signs of old age, and is used in this context in reference to the frost, which makes trees and bushes look like white hair. (U.S. Air Force photo by Staff Sgt. Brian Stives)