Daylight Saving Time - Blog Posts

Daylight Saving Time, Edo style

These Edo-period clocks are on display at the National Museum of Nature and Science in Ueno, Tokyo. They are unusual in two ways: the display looks kind of like a ruler, and you may notice on the left example that the marks are irregular. This would seem to suggest that hours in one half of the day are considerably shorter than in the other half.

The basic idea is that the Sun always rose at 6 in the morning and always set at 6 in the evening. In between, the same number of hours, no matter the season. This means that in the summer, an hour was quite a bit longer than an hour in winter, and vice-versa for the nights. It turns out the Romans were doing this too, on a more elementary scale as their clocks were sundials, and soon noticed that they weren't getting as much rest at some times of the year...

Today, most of Europe and the US have Daylight Saving Time, and we're going through the "ugh, clocks forward, less sleep" movement in Europe tonight. But let's take a moment to consider that the owners of these clocks would have owned a set of rulers and changed them each month!