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.
The "archin" is an obsolete unit of length that was historically used in Russia and other parts of the former Soviet Union. The length of an archin varied by region and over time, but it was typically around 28 inches or approximately 71 centimeters. In some regions, an archin could be slightly shorter or longer.
The archin was used for measuring cloth, textiles, and sometimes land. Like many traditional units of measurement, it has largely been replaced by more standardized systems, such as the metric system, in modern times. While the archin is no longer commonly used for official measurements, it may still be encountered in historical or traditional contexts in Russia and other former Soviet states.