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.
A "fingerbreadth" is a unit of length that is approximately equal to the width of an adult human finger. It is often used informally and in various historical and cultural contexts as a convenient way to estimate small lengths or distances. The actual measurement of a fingerbreadth can vary somewhat depending on the size of an individual's finger, but it is typically around 1 inch (about 2.54 centimeters) or slightly less.
In some historical systems of measurement, particularly in ancient cultures, the fingerbreadth was used as a standardized unit for measuring length. It was one of the smaller units within a larger system of measurement, often used for small-scale applications like measuring the dimensions of objects, architectural details, or jewelry.
While the fingerbreadth is not a commonly used unit of measurement in modern times, it remains a useful and intuitive way to approximate small lengths informally, especially when a quick estimate is needed.