If you aren’t particularly interested in dams, you might think that the day passes more slowly if you have to spend much time contemplating them. There is, however, a direct correlation between one particular dam and the length of the day. The Three Gorges Dam is so massive that it actually slows the speed at which the earth rotates.

Three Gorges Dam, spanning the Yangtze River in China.

Located near Sandouping, China, the Three Gorges Dam is beyond massive. Completed in 2012 at an estimated cost of $25-37 billion, the dam is constructed of 510,000 tons of steel and concrete. It is 7,661 feet (2,335 meters) long and almost 600 feet (183 meters) high. It spans the Yangtze River and holds back 10.14 trillion gallons (39 trillion kilograms) of water to 575 feet (175 meters) above sea level.

To make room for the project, 140 towns, 13 cities, and 1,600 settlements were destroyed and 1.2 million people were relocated by the Chinese government.

As a result of holding back so much water, the dam has actually had an effect on the earth’s rotation. By displacing the water, it slightly changed the earth’s center of gravity, thereby slowing the amount of time it takes to rotate.

NASA has calculated that the dam adds 0.06 microseconds (six hundredths of a millionth of a second) to the length of the day. If you have had one of those days that just seems to drag on forever, you aren’t imagining things. The Three Gorges Dam is partially responsible.

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