The human body relies on sunlight to synchronize its internal clock. Light controls the release of hormones that tell our bodies whether it’s time to be alert or time to sleep – despite most of us needing an alarm clock to wake up. Most other animals, even those that are nocturnal, use sunlight to maintain their internal clocks as well. But animals living close to either of Earth’s poles need a different strategy during the long months of winter when there’s hardly any sunlight at all.
In Print: January 1, 2022