Planet. The planet formerly known as "Pluto" was named for the Roman god of the underworld.

Footcandle. One foot-candle is equal to 10.76391 lux.

Environmental Protection. Pollution in China has made cancer a leading cause of death in 30 cities and 78 counties.

Eratosthenes. Eratosthenes used geometry, trigonometry, and a well in Alexandria, Egypt, to calculate the earth's diameter.

Oxygen. The chemical formula of water is H2O.

Newton's Third Law. Newton's Third Law says that action and reaction are simultaneous.