Exploring Daylight Savings Time Illuminates Fascinating History and Science
Guided by the expression, “Spring ahead, fall back,” daylight savings time has once again dictated that we move our clocks back by an hour. Though we can all celebrate the extra hour of Saturday-night sleep that we were granted through this practice, that isn’t all that daylight savings time isn’t just about extra sleep or the saving of daylight. Examining the history of daylight savings time can illuminate the worldwide use of the practice is closely tied to human history, and exploring the reasons behind the changes in sunlight that drive daylight savings time can lead to the development of new scientific understandings!
While the name of our clock-changing practice implies that it somehow allows us to save daylight, what daylight savings time actually does is allows the daylight hours during the summer months to be better aligned with the hours during which humans are most active. Early proponents of the practice saw daylight savings time as an opportunity to save on energy costs, beginning with Benjamin Franklin who (though jokingly) suggested in the late 18th century that getting up earlier in the morning would save on candle costs. Daylight savings time was first practiced in Europe, where Germany adopted it in order to save coal to fuel war preparations. The United States adopted daylight savings time in 1918 for similar reasons.
Today, all but two US states follow daylight savings time (those abstaining are Hawaii, land of perpetual sunshine, and Arizona, where extra sunshine means higher energy bills). Internationally, 70 countries switch their clocks with the seasons, meaning that over a billion humans are affected by the use of daylight savings time. The idea of adjusting our schedules to match hours of daylight isn’t an entirely modern practice, though. The history of daylight savings can be traced back as far as Roman times, where water clocks were adjusted monthly to keep humans’ schedules in line with the earth’s natural daylight changes.
As the Romans noticed, the amount of sunlight hours in a day changes constantly throughout the year – whether we change our clocks or not. Thanks to the tilted axis upon which the earth spins, combined with the shape of its orbit around the sun, the length of time during which sunlight reaches the earth changes with the seasons. When the earth’s tilted axis brings the Northern Hemisphere closer to the sun than the Southern Hemisphere, daylight hours come in abundance. But when the earth pushes the north further from the sun and the south closer, those of us in North America experience longer hours of darkness.
Families can further explore the science behind this phenomenon by participating in Journey North’s Mystery Class, a science-based global scavenger hunt that uses clues related to daylight hours, sunrise and sunset times, and latitude and longitude to help participants locate hidden locations all over the globe. While Mystery Classroom doesn’t begin until January (and uses the onset of spring to spark studies of the reasons for seasons), Journey North offers materials to help families prepare for the spring challenge. Folks planning to participate can prepare by beginning to track changes in day length in their geographic location, allowing them to compare the change in photoperiod over a long period of time. Seeing concrete evidence of the change in daylight can help young scientists conceptualize the incredibly subtle changes that are taking place around them every day!
[Photo credit: (cc) Randy Robertson]