17 October 2026

 

Across much of Europe and North America, autumn brings an unusual ritual: turning the clocks back and living through the same hour twice. Daylight saving time ends, evening darkness arrives earlier by the clock, and anyone sleeping through the proceedings gets an opportunity for a longer night.

Whether our brain accepts the invitation is another question. Changing a clock takes seconds; adjusting the timetable inside your body can take longer.

 

Why do clocks go back in autumn?

 

Summer time, also called daylight saving time, moves clocks forward in spring to place more daylight in the evening. A sunrise at 05:00 becomes 06:00; a sunset at 20:00 becomes 21:00. More daylight then falls after work or school, leaving time for cycling, gardening or sitting outside.

Energy conservation helped turn the idea into policy. Seasonal clock changes were adopted in Europe during the First World War and reintroduced in many countries during the 1970s. Moving activity into daylight could reduce demand for artificial lighting.

Turning back in autumn restores standard time, bringing daylight earlier into our morning schedules. The days themselves are shortening because Earth’s tilted axis changes each hemisphere’s exposure to sunlight as the planet orbits the Sun. Adjusting the clocks makes the retreat of evening light feel particularly abrupt.

 

How your body clock keeps time

 

Inside the hypothalamus, deep in the brain, sits the suprachiasmatic nucleus, or SCN. This small cluster of nerve cells acts as a central timekeeper, helping coordinate circadian rhythms: roughly 24-hour cycles in processes including sleepiness, body temperature and hormone secretion.

Its mechanism involves molecular feedback loops. Clock genes drive the production of proteins that accumulate and help suppress their own production. As those proteins break down, the cycle starts again. Related mechanisms operate in cells throughout the body, with the SCN helping keep their rhythms coordinated.

Light synchronises this machinery with the outside world. Specialised light-sensitive cells in the retina send information to the SCN, which also influences the pineal gland’s production of melatonin through a chain of nerve connections. Melatonin signals biological night, helping prepare the body for sleep.

 

Why the clock change can disrupt sleep

 

After the autumn change, your previous 07:00 waking time becomes 06:00. If your internal rhythm initially keeps its old timing, you may wake early despite having permission to sleep longer. Sleepiness can likewise arrive earlier by the new clock as the earlier sunset does not instantly switch on melatonin production. Its timing reflects your circadian rhythm and exposure to light, including artificial lighting.

Autumn is generally easier to accommodate than spring, which requires an earlier start relative to biological time and can reduce sleep. Nevertheless, returning to standard time can still disturb sleep patterns.

 

Why some people oppose summer time

 

Disliking seasonal changes and opposing summer time are different positions.

Supporters of permanent summer time value later sunsets. Keeping that arrangement through winter would, however, also delay sunrise, leaving more morning activity in darkness.

Sleep specialists have another concern. Morning light generally helps shift biological rhythms earlier, while evening light can delay them. Summer time places daylight later relative to fixed school and working schedules. The American Academy of Sleep Medicine consequently advocates permanent standard time as the better fit for human circadian biology.

That choice would bring earlier summer sunrises and sunsets. The disagreement involves competing priorities: morning light, evening recreation and schedules that cannot easily move. Meanwhile, the European Commission has argued that energy savings no longer justify seasonal changes. 

 

When an hour happens twice

 

Whatever governments decide, software must follow. Many devices rely on time-zone databases containing local clock rules, receiving updates through their operating systems. During the repeated hour, a time such as 01:30 or 02:30 can describe two different moments. Including its offset from Coordinated Universal Time distinguishes them. 

Political coordination is less automatic. The European Parliament backed ending seasonal changes in 2019, but the Council has yet to agree its position, so the existing system continues. 

For anyone struggling with the adjustment, morning daylight and reasonably consistent sleep schedules can help. Give yourself time to settle rather than expecting your biology to update as promptly as your phone.

And resist spending the bonus hour scrolling in bed. Your phone may know the time, but that does not make it a qualified sleep companion.