Earth's diameter isn't a single, fixed number because the planet isn't a perfect sphere. It bulges slightly at the equator due to its rotation. Therefore, we need to consider different diameters:
Equatorial Diameter
The equatorial diameter, measured across the Earth at the equator, is approximately 12,756 kilometers (7,926 miles). This is the widest diameter of the Earth. Multiple sources, including NASA (https://science.nasa.gov/earth/facts/), confirm this measurement. For example, NASA states that Earth has an equatorial diameter of 7926 miles (12,760 kilometers). Another source, Cool Cosmos (https://coolcosmos.ipac.caltech.edu/ask/57-How-large-is-Earth-), also gives the diameter as 7,926 miles (about 12,756 kilometers).
Polar Diameter
The polar diameter, measured from the North Pole to the South Pole, is slightly smaller than the equatorial diameter. It is approximately 12,712 kilometers (7,900 miles). This difference is due to the Earth's rotation causing it to bulge at the equator. The difference between the equatorial and polar diameters highlights Earth's oblate spheroid shape. A source, NSSDCA (https://nssdc.gsfc.nasa.gov/planetary/education/schoolyard_ss/sss_earth2m.html), gives the actual diameter as 12,712 km.
Average Diameter
Often, a mean or average diameter is used for simplicity. This is approximately 12,742 kilometers (7,918 miles). This value represents a compromise between the equatorial and polar diameters.
In summary, while various sources may offer slightly different figures due to variations in measurement techniques and the Earth's slightly oblate shape, the generally accepted values for Earth's diameter are consistently around 12,756 km (equatorial) and 12,712 km (polar).
