The Arctic Circle in the middle of winter is so dark it's hard to see. Because of the way the top of the Earth tilts away from the sun, the star never appears to rise above the horizon, and dark skies drench the Arctic in what’s known as polar night.

“It kind of feels like you’re working the night shift all the time,” says Finlo Cottier, an oceanographer at the Scottish Association for Marine Science.

Two years ago, Cottier and a team of scientist traveled to the Arctic in the middle of winter to study how light affects the marine critters living in far northern waters. Like us, marine organisms rely on light to guide their daily functions. Light indicates behavior like