Let it snow
- Snowflakes are formed as water vapour condenses and freezes onto a seed crystal, which itself forms on a small particle such as a speck of dust, and then crystallizes. They are not, as commonly thought, frozen raindrops, which is actually known as sleet.
- Snowflakes, a single crystal of ice also known as snow crystals, can come in a variety of shapes depending on temperature, humidity and cloud height. At warmer conditions snowflakes grow slower, creating less intricate shapes whereas colder temperatures or high humidity lead to branching of the arms (dendrites). High clouds produce six-sided hexagonal crystals such as fernlike stars, medium-height clouds form needles, hollow columns or flat hexagonal plates, and low clouds produce a variety of six-sided shapes.
- The six-sided symmetrical snowflake shape is due the atomic structure of water molecules, which form weak bonds (hydrogen bonds) with each other. Water molecules order themselves in predetermined spaces creating the symmetrical hexagonal shapes seen in snowflakes.
- Snow is seen as white due to the complex structure of snowflakes which means each of its many tiny surfaces reflect light, and the little light absorbed by the snow is done so uniformly across the wavelengths of the visible light spectrum.
- The familiar crunching sound you hear as you step on snow is the air being compressed and pushed out of the snow.
- To catch a snowflake simply put some thin cardboard and acetate sheets in the freezer, and place a can of spray acrylic (available in art supply stores) outside. Fasten a sheet of acetate to a piece of cardboard with two clothes pegs, and spray the acetate with a thin coat of acrylic. Hold this up by the clothes pegs until a few individual flakes have collected on the sheet, and leave outside protected by a cardboard box for an hour. The snowflakes should then evaporate, leaving you with acrylic replicas!
- Finally the question you most desperately want to find out – will it be a white Christmas? Unfortunately for most parts of the UK, Christmas is right at the start of the snow period, so snow is most likely to fall between January and March. All levels of the atmosphere need to be below freezing to allow snowflakes to form, and fall to the ground undisturbed, however with climate change bringing higher temperatures over land and seas the chances of a white Christmas are becoming less and less likely.