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.
A furlong is a unit of length that is used primarily in horse racing and some other sports, as well as in some older systems of measurement. In modern terms, one furlong is equal to 1/8th of a mile. This is equivalent to 660 feet or 220 yards.
The term "furlong" has historical roots and was originally used in medieval England as a way to measure distances for plowing fields. Over time, it became associated with horse racing and is still used today to describe the length of a horse racing track. In horse racing, races are often measured in furlongs, and the distance of a race may be referred to as "6 furlongs" or "10 furlongs," for example.
While the furlong is not commonly used in everyday measurements, it is still relevant in certain specialized contexts, particularly in horse racing and related sports.