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).
The "cubit" (Greek: πῆχυς, pēchys) in ancient Greece was a unit of length used in antiquity for measuring various objects, including architectural dimensions. Like many ancient units of measurement, the length of the Greek cubit could vary over time and by region.
The most commonly referenced Greek cubit is the "common" or "short" cubit, which is believed to have been approximately 45 centimeters (about 17.7 inches) in length. However, there were variations in the length of the cubit in different parts of Greece and during different periods in ancient history.
The Greek cubit was used for measuring building dimensions, as well as in various crafts and trades. It was often based on the length of the forearm from the elbow to the tip of the middle finger, much like other cubits used in different ancient cultures.
It's important to note that the length of the Greek cubit is a matter of historical interpretation and may not be precisely defined due to variations in antiquity.