hiya hudax 
"Your biological clock resets itself every day by the appearance of
morning light. That's why you can, over a few days, adjust your
clock if you fly to some other continent, or even across one. As
you may know, our biological clocks are not perfect 24-hour
machines. They drift a little bit every day. Most people drift
toward a longer day (their clock takes more than 24 hours to
complete a cycle). This is probably why most people find it easier
to stay up late than to wake up early. For some people, that drift
toward later hours can be very dramatic. They may be the ones who
most need to learn about what I'm presenting here. They don't stay
glued to "real time" very well. They need to avoid getting
"unglued" any further. And light at night may be one of the most
important ungluing factors."
