Geek Trivia

What Determined The Direction Of Clock Hand Movement?

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Sundial on the campus of the U.S. Naval Hospital in San Diego
Edward Gohlich/Library of Congress

Answer: Sundials

The hands of clocks and watches rotate from the upper right quadrant of the clock face down to the lower right, around to the lower left, and then back up around through the upper left until they arrive in the upper right quadrant—a familiar movement we simply refer to as clockwise.

But why this right-to-left rotation? Clocks could have just as easily been constructed to rotate in the opposite direction, after all. To understand the rotational direction of clock hands, we need to turn to the clock’s predecessor and where the first clock faces and clock hands were constructed. Prior to clocks, people used the sun to tell time, often in the form of a sundial.

The first clocks with hands were constructed in the Northern Hemisphere and a horizontal sundial in the Northern Hemisphere has a shadow that rotates from the upper right around to the lower left and back up again; early clockmakers simply mimicked this familiar motion. Modern clock hands are simply following the same path as the shadows cast by the sundials that preceded them.

Curiously, there are some early exceptions. South-facing vertical sundials have a shadow that moves counter-clockwise and a few early clocks were constructed to follow the shadow path produced by them. Few examples of these older counter-clockwise clocks exist, but a remarkably well-preserved one can be seen in the Münster Cathedral located in Münster, Germany. The Münster astronomical clock not only tells the time with an hour hand that traces the actual path of the sun, but also has minor hands that track the positions of the planets and even has a moon-phase indicator.