Why do clock hands turn clockwise?

In the Northern Hemisphere, the sun rises in the east, crosses the southern sky, and sets in the west. So the shadow of the stick on a flat sundial points west in the morning, swings through north, and moves to the east by evening. Seen from above, that is exactly the direction clock hands turn today.

When mechanical clocks first appeared in 14th-century Europe, people were already used to sundials. The new clocks are thought to have turned their hands and laid out their numbers in the same direction the shadow moved. NASA's education material also mentions the claim that the word “clockwise” came about this way.

Some people think clocks in Southern Hemisphere countries turn the other way. In fact, clocks in Australia or Brazil turn in the same direction as ours. Mechanical clocks spread from Europe in the north, and that design became a worldwide convention.

In the Southern Hemisphere the sun crosses the northern sky, so a flat sundial's shadow turns the other way. If clocks had first been made in the south, the hands might have turned the opposite way.

In June 2014, Bolivia's government changed the clock atop its Congress building to turn to the left and reversed its numbers. It was a symbol of the country's identity as a Southern Hemisphere nation. In tropical places like Bolivia, though, a sundial's shadow can turn to the right for a few months of the year.

No old record directly stating the sundial origin has been confirmed either. There is also the objection that shadows on wall-mounted sundials turn the other way, so it is best seen as the most plausible explanation.

The direction of clock hands has become a way of describing direction. Instructions like “turn clockwise to close” use it, and pilots or rescue teams treat straight ahead as 12 o'clock and give positions like “3 o'clock.” Saying a running track is circled “counterclockwise” also uses the clock as the reference for the other way. These words still work now that digital clocks are common because everyone pictures the movement of a round clock face the same way.