These pictures show real snow crystals that fell to earth in Northern Ontario, Alaska, Vermont, the Michigan Upper Peninsula, and the Sierra Nevada mountains of California. They were captured by Kenneth G. Libbrecht using a specially designed snowflake photomicroscope.
A dense network of blood vessels in the alveoli enables the quick transfer of oxygen to the bloodstream in the lungs. Here blood cells can be seen squeezing through the narrow capillaries. Taken by professional science photographer Oliver Meckes, the image won second prize in the competition.