A parsec (abbreviated as pc) is a unit of measurement used in astronomy to express vast distances, primarily for indicating the distances between celestial objects such as stars and galaxies. The term "parsec" is derived from "parallax of one arcsecond," and it's based on the principle of parallax.
In simple terms, a parsec is defined as the distance at which an object will have a parallax angle of one arcsecond when observed from Earth. Parallax is the apparent shift in the position of an object when viewed from two different vantage points, in this case, from opposite sides of Earth's orbit around the Sun.
The exact value of a parsec is approximately 3.086 x 10^16 meters (about 3.09 trillion kilometers or 1.92 trillion miles). This unit of measurement is particularly useful for describing astronomical distances because it provides a convenient scale for expressing distances within our galaxy, the Milky Way, and nearby galaxies.
In summary, a parsec is a unit of length used in astronomy to describe distances on an astronomical scale, with 1 parsec being roughly equivalent to 3.09 trillion kilometers or 1.92 trillion miles.