The inner clock: light, melatonin and the clock change
About this app
A 24-hour clock face with a wall clock and an inner clock: without daylight the inner clock runs a little over 24 hours and falls behind every day; morning light resets it. Melatonin rises in the evening. At the clock change only the wall clock jumps; the inner clock needs a few days (mini jet lag, autumn and spring compared).
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
The clock in the body
A pacemaker in the brain, the suprachiasmatic nucleus, gives the body a rhythm of about one day, the circadian rhythm: we get tired in the evening, and body temperature drops at night. Without daylight this inner clock runs at about 24.2 hours on average in humans, a good 10 minutes later every day. Light, especially in the morning, resets it daily through light-sensitive cells in the retina. In the evening the pineal gland releases the hormone melatonin, about two hours before the usual bedtime; bright light suppresses it.
What you see
A 24-hour clock face with two hands: the thin one is the wall clock, the thick one the inner clock. Around it a ring of day and night, inside it the melatonin band and bedtime. Next to it the melatonin curve over 24 hours and a chart that shows for each day how many minutes the inner clock is ahead or behind. Four cases: with daylight, without daylight, the clock change in autumn and in spring. The adjustment over the days is a model, not a measurement.
Things to try
Choose “without daylight” and play the week: every day the inner clock falls 12 minutes behind. Switch to “autumn change” and go from day −1 to day 0: the wall clock jumps from 3:00 to 2:00, the inner clock does not. Watch the bar shrink over the following days, then compare with spring.
Frequently asked questions
- What is the circadian rhythm?
- An inner rhythm of about one day (Latin circa diem), produced by a pacemaker in the brain. It controls tiredness, body temperature and hormones such as melatonin. Without outside time cues it runs a little longer than 24 hours in humans on average; light resets it every day.
- How long does the body need after the clocks change?
- Usually a few days. After the autumn change the inner clock is one hour ahead: people get tired earlier and wake up earlier. Studies show that many people adjust in autumn but less well in spring, especially late chronotypes.
- What does melatonin do?
- Melatonin is a hormone from the pineal gland that signals night to the body. It rises in the evening about two hours before the usual bedtime, stays high at night and falls in the morning. Bright light, screens included, suppresses its release.
- What can I change in the app?
- The case (with or without daylight, autumn or spring change), the day from −1 to 7 and the time. Drag on the clock face to change the time and in the day chart to move through the days.
Subject: Biology (Gymnasium)
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