Earth's equatorial radius, often denoted as "R," is the distance from the center of the Earth to the point on the Earth's surface that lies along the equator. It represents the Earth's average radius when measured from its center to its equatorial surface. The equatorial radius is greater than the polar radius because the Earth is slightly flattened at the poles and bulges at the equator due to its rotation.
The approximate value for Earth's equatorial radius is about 6,378.1 kilometers (or approximately 3,963.2 miles). This value may vary slightly depending on the reference ellipsoid used for modeling the Earth's shape, but the given value is a commonly used and accurate approximation for most purposes.
In contrast to the equatorial radius, Earth's polar radius (measured from the center to a point on the Earth's surface at the North or South Pole) is slightly shorter, approximately 6,357 kilometers (3,949 miles).
A rod is a unit of length used in some systems of measurement, primarily in the United States and the United Kingdom. In the U.S. customary system, one rod is equal to 16.5 feet or 5.0292 meters. It is also equivalent to 1/4 of a chain, which is another traditional unit of length.
Rods were historically used for land measurement, particularly in surveying and real estate. In some cases, you may still come across the use of rods in property descriptions, especially in rural or agricultural areas. However, the use of the rod as a standard unit of measurement has become less common in favor of more standardized systems like the metric system or the U.S. customary system based on feet and yards.