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Image of the day – 152
What’s in an image? Sometimes quite a lot, more than meets the eye. I’m posting an image every few days.
It’s a pretty picture, isn’t it? Red berries in wintertime, covered with glistening ice crystals. I used this photo once for a Christmas card. The ice is very decorative, and it’s easy to understand why we talk about icing on a cake (frosting in the USA).
The ice crystals form as the air cools at night. Air can hold significant amounts of water in gaseous form, but the precise amount depends on the temperature of the air; warm air can hold much more water than cold air. That’s why water condenses on cold surfaces. Take something out of the fridge and leave it in a warm room, and five minutes later it will be covered in droplets of water. That water was in the air but you couldn’t see it or feel it because water vapour is a gas.
During a summer night, molecules of water in the air condense as droplets of water on leaves, we call it dew. But on a cold winter’s night the water condenses as ice and we call it frost. Hoar frost, or rime, forms slowly over a number of hours and the kind of ice crystals that form is dependent on humidity, pressure and rate of temperature change. It can be quite subtle (view ‘The snowflake designer’ below for the details).
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