70. How does the photoperiod effect people?
When people travel over great distances in a plane, time zones are covered rapidly. Exposure of sunlight sets our internal clock. The amount and duration of the sunlight brings our internal systems into synch. When a person is rapidly exposed to a different amount and duration of sunlight, the bodies systems drift apart and the person feels a bit disoriented (jet lag). A few days exposure to the new photoperiod quickly brings the bodies internal systems back into synch.