Parsec
A parsec (pc) is a unit of distance used in astronomy, equal to about 3.26 light-years or roughly 31 trillion kilometers. The name “parsec” comes from “parallax of one arcsecond,” referring to the method astronomers use to measure distances to nearby stars based on their apparent shift when viewed from different positions in Earth’s orbit. Parsecs are commonly used to measure distances to stars and galaxies. For example, the nearest star system, Alpha Centauri, is about 1.3 parsecs away. The symbol for parsec is "pc". It’s a convenient unit for expressing large astronomical distances beyond the reach of light-years.
Chain
A chain is a unit of length traditionally used in land surveying. The most common version is the Gunter’s chain, which equals 66 feet or 22 yards, approximately 20.1168 meters.
The chain was introduced by English clergyman Edmund Gunter in the 17th century to simplify land measurement. One chain consists of 100 links, each 0.66 feet long. It became a standard unit in British and American land surveying and was instrumental in defining land areas, especially in the U.S. Public Land Survey System.
Key Conversions:
1 chain = 66 feet
1 chain = 22 yards
1 chain ≈ 20.1168 meters
10 chains = 1 furlong
80 chains = 1 mile
Though now largely replaced by metric units and modern surveying tools, the chain still appears in older land deeds, maps, and rural property descriptions.