In the United States surveying system, an "inch" is a unit of length, but it is not significantly different from the standard inch used in everyday measurements. An inch in U.S. surveying is equal to 1/12th of a foot, just like the standard inch. This means that one U.S. survey inch is approximately equal to 0.0833333 feet or about 2.54 centimeters.
The primary distinction in U.S. surveying is the use of the survey foot, which is defined as exactly 12 survey inches. This slight difference in the definition of the foot and inch in U.S. surveying is used for precise land measurements and surveying work, especially when dealing with large areas of land. However, for most everyday purposes, the standard inch and foot are used in the United States and other countries that employ the imperial system.
A megaparsec (Mpc) is a unit of measurement used in astrophysics and cosmology to express vast distances on cosmic scales. It is equal to one million parsecs. A parsec (pc) is a unit of length used in astronomy to describe astronomical distances, and it is approximately equal to 3.09 × 10^16 meters or 3.09 × 10^13 kilometers.
So, a megaparsec is equivalent to:
1 megaparsec (Mpc) = 1,000,000 parsecs (pc)
Megaparsecs are typically used to describe distances between galaxies and galaxy clusters in the universe. Since astronomical distances are extremely large, the parsec and its multiples, such as the megaparsec, provide a convenient way to express these distances without dealing with unwieldy numbers of kilometers or light-years. Cosmologists often use megaparsecs when discussing the large-scale structure of the universe, the size of galaxy clusters, and the expansion of the cosmos.