Reading the sky from a single crystal

Last winter I spent eleven nights on a ridge above Tokachi with a cooled glass slide and a single oblique lamp, waiting for crystals that would not arrive on demand. The trick Nakaya taught in 1954 is not to photograph the snow but to read it: a plate means one set of conditions aloft, a needle means another, and a capped column means the air changed its mind on the way down.

The grid does the arguing

Plot temperature left-to-right and humidity bottom-to-top, drop each specimen into its cell, and the taxonomy stops being decorative. A stellar dendrite at −15°C is not a prettier version of a hollow column at −6°C; it is a different sentence written by a different atmosphere. The dark field — white-cyan figure floating on near-black ground — is what lets the six-fold symmetry speak without ornament getting in the way.