Daylight saving time shifts clocks forward in spring and back again in autumn in many countries.

The longer version

Shifting clocks forward in spring moves an hour of daylight from the morning into the evening, when more people are awake. Clocks return in autumn. The change does not create light; it only relabels the hours at which daylight arrives. Places at higher latitudes notice the effect most, because daylength swings widely.

The idea was promoted as a fuel-saving measure during wartime and then kept by many countries. Studies of actual savings give mixed results, and modern lighting patterns reduce the benefit. Arguments now focus on sleep disruption, since the spring shift costs most people an hour of rest on the following night. Several regions have abandoned the practice after public pressure.

Where this entry sits

These facts wander through clocks, calendars, time zones, and the long human effort to measure passing hours. You will find leap years, odd month lengths, ancient sundials, and the reasons modern timekeeping works the way it does. The full list sits on the Time and Calendars page, where every entry is listed in order.