Shunxuan He

Light from a distant star cuts through dust like a flashlight beam through fog. Dust holds back blue rays more than red ones, making the star appear redder than it really is. From this reddening, astronomers gauge how much dust lies in the light's path.

An old lighthouse at the edge of the harbor blinks with the precision of a clockwork mechanism. Every few hours its lamp flares and dims, and sailors recognize that rhythm from afar, using the strength of the light to tell where the shore lies.