A parsec (pc) is a unit of measurement used in astronomy to describe astronomical distances, particularly on cosmic scales. The term "parsec" is actually a contraction of "parallax of one arcsecond," which refers to the method by which this unit of distance is defined. A parsec is defined as the distance at which an object will appear to shift its position by one arcsecond (1/3,600th of a degree) as observed from Earth when the Earth is on opposite sides of its orbit (at an average distance of one astronomical unit, or about 93 million miles) from the Sun.
In more practical terms, a parsec is approximately equal to 3.09 × 10^16 meters or 3.09 × 10^13 kilometers.
To provide a sense of scale, some common astronomical distances expressed in parsecs include:
Parsecs are especially useful for describing distances between stars and galaxies, as astronomical distances can be incredibly vast, and using kilometers or even light-years can lead to unwieldy numbers.
In the United States surveying system, a "link" is a unit of length that is equal to 1/100th of a chain. Each link is approximately 7.92 inches long or about 0.201168 meters. This unit is primarily used in surveying and land measurement in the United States.
Surveyors often use a chain, which is comprised of 100 links, to measure distances in land surveys. The use of links and chains allows for precise measurements of land parcels, boundaries, and property lines.