Morning light helps reset the internal clock, which is why jet lag fades gradually.

The longer version

Light hitting the retina early in the day sends signals along a pathway to the master clock, shifting the schedule earlier or later depending on when the light arrives. Morning exposure generally pulls it forward, while evening exposure pushes it back. The effect depends on intensity and duration, so indoor room light acts far more weakly than daylight.

The shift is small each day, roughly an hour or so, which is why recovery after long flights takes several days rather than one. Regular mealtimes and exercise can serve as secondary timing signals, which is one reason routines help after travel. This limited daily adjustment is also why eastward travel often feels harder than westward travel.

Where this entry sits

This collection gathers curious details about sleeping and dreaming, from nightly brain stages and body clocks to naps, yawns and unusual animal habits. It also covers how bedtime customs have changed across centuries, without offering any advice. The full list sits on the Sleep and Dreams page, where every entry is listed in order.