A clock with hands (an analogue clock) shows us the numbers 1-12. There are 24 hours in one day, so we measure time by splitting the day into two halves. The first 12 hours of the day, from ...

Daylight and Earth’s 24-hour clock are at the very heart of evolution. “The Inner Clock” offers a rich history of what makes us tick, so to speak, paired with fascinating modern discoveries ...

The brain has a master clock that is set by exposure to sunlight and darkness. This circadian rhythm is a roughly 24-hour cycle that determines when we become sleepy and when we’re more alert.

Here’s what to know about the twice yearly ritual. The brain has a master clock that is set by exposure to sunlight and darkness. This circadian rhythm is a roughly 24-hour cycle that determines when ...