Chinese naturalists may have discovered the six-sided nature of snowflakes over a thousand years before Europeans caught on; an ancient text dating from 135 B.C. mentions the six-pointed nature of "snow flowers."
In 1611, German astronomer Johannes Kepler caught up with a treatise on the six-fold symmetry of snowflakes, but he was baffled as to how the intricate shapes were created. Libbrecht explains that it wasn't until the development of X-ray crystallography in the 1920s that researchers were able to study the atomic structure of ice crystals to determine how they formed. "X-rays have about the same wavelengths as the spacing between atoms in crystals," Libbrecht explains.