A "hand" is a unit of measurement commonly used in the context of measuring the height of horses. In the United States and some other English-speaking countries, a hand is defined as exactly 4 inches or 10.16 centimeters.
Horses are typically measured in hands from the ground to the highest point of their withers (the ridge between the shoulder blades). This measurement is a convenient way to describe a horse's height without relying on feet and inches or meters.
For example, a horse that measures 15.2 hands is 15 hands and 2 inches tall. Horses can vary in height, and the hand system provides a standardized way to communicate a horse's size, which is particularly important in horse racing, equestrian sports, and the horse industry in general.
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).