For a few days after Christmas, the world in Shropshire was sugared with soft ice crystals. Magical!!!
Frost is to dew as snowflakes are to raindrops. When water vapor condenses into liquid water, you get raindrops and dew. When water vapor condenses directly into ice, then you get snowflakes and frost. Snowflakes are not frozen raindrops, and likewise frost is not frozen dew.
When frost forms as minute ice crystals covering the ground, we just call it all frost. But sometimes the frost grains grow larger and are called hoar frost crystals. Hoar frost grows whenever it’s cold outside and there is an ample source of water vapor nearby. On clear, cold nights in winter soft, interlocking ice crystals may form on any object that has been chilled to below the freezing point and becomes colder than the surrounding air. “Clear moon, frost soon”. The formation of hoar frost is similar to the formation of dew with the difference that the temperature of the object on which the hoar frost forms is well below 0°C.
Hoar frost first turns up in written English in 1290 as hore frost. Strictly speaking, hoar frost is the kind of frost that turns everything it forms upon white or gray. Due to the fact that hair turns gray with age, things that are white or gray are often associated with old age and this is the original sense of hoar. Old English har and Old High German her both meant “old” or, as a secondary meaning, “venerable, august”.
“Enough with the science and etymology lessons already. Time to go back to the cottage for some mulled wine!”