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.
"Aln" is a unit of length that is used in some parts of Scandinavia, particularly in Sweden and Norway. The term "aln" is derived from the Old Norse word "alinn," which means "forearm." Historically, it was a common unit of measurement for cloth, textiles, and land.
The exact length of an aln could vary by region, but it was generally around 2 Swedish feet or approximately 59.4 centimeters (or about 23.4 inches) in Sweden. In Norway, an aln was somewhat longer, typically around 62.7 centimeters (about 24.7 inches).
The use of the aln as a standard unit of measurement has largely been replaced by the metric system in Scandinavia and most parts of the world, but it may still be referenced in historical or traditional contexts.