Your Internal Clock
Why you wake up moments before your alarm
Your body has an internal timekeeper that runs on roughly a 24-hour cycle and tracks not just sleep and wake, but fine-grained intervals throughout the day. At its center is the suprachiasmatic nucleus, a small cluster of neurons in the hypothalamus that coordinates circadian rhythms across every organ. Light is its most powerful signal.
You notice it in small ways all the time. You get sleepy around the same hour each night. You wake up moments before your alarm. You feel alert at 10 AM and foggy at 3 PM, regardless of how much coffee you've had. This is also why jet lag is so disorienting: your body isn't just tired, it's actively expecting things at the wrong moments. Bright morning light and a consistent sleep schedule are the most powerful tools for keeping the system tuned.
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Your Internal Clock