|Heimler, Neil. Principles of Science. Columbus, OH: Merrill, 1992.||"12,756 km"||12,756 km|
|World Book Encyclopedia. Chicago: World Book.||"12,713 km"||12,713 km|
|"Earth" Encarta. Microsoft, 1996.||"12,756.3 km"||12,756.3 km|
|Earth, Space and Time: An Introduction to Earth Science. New York: Wiley, 1979.||"12,752 km"||12,752 km|
|earth. Infoplease.com.||"The equatorial diameter is c.7,926 mi (12,760 km) and the polar diameter 7,900 mi (12,720 km)"||12,760 km
The Earth is the fifth largest planet of the solar system. The reason why earth is in a spherical shape, is because of the gravitational pull. The number that appeared most often in my sources was 12,756 km. There are actually two diameters of Earths: equatorial and polar. One of my sources stated that the equatorial diameter is 40 kilometers wider than the polar diameter. The Earth is not a perfect sphere because of a bulge in the equator. Most of the current knowledge of the Earth has been collected in three methods, through satellites, telescopes and outer space exploration.
Ricardo Martinez -- 1999