Rainbow lines cut through the darkness in photographer Stephen Orlando’s images of a kayak in motion. Equipped with an LED-lined paddle, Olympic kayaker Adam van Koeverden paddled along the waterfront while Orlando took long exposure photographs. The kayak’s motion makes it effectively invisible, while the paddle’s lights trace out the path of each stroke taken. Scientists also use this kind of technique to follow the path of an object in a flow. In fluid dynamics, we call these remnants of an object’s trajectory a pathline. (Image credit: S. Orlando)