A parsec is a unit of distance used in astronomy to measure large distances between astronomical objects outside our solar system. It stands for “parallax of one arcsecond.” The concept of a parsec originates from the method of astronomical parallax, which involves measuring the apparent shift in position of a nearby star against the backdrop of more distant stars as observed from Earth at different points in its orbit around the Sun.
One parsec is the distance at which one astronomical unit (AU) subtends an angle of one arcsecond. An astronomical unit is the average distance from the Earth to the Sun, approximately 149.6 million kilometers or about 93 million miles. Since one degree is equal to 3,600 arcseconds, using trigonometry and the small angle formula, we can calculate that 1 parsec is equivalent to about 3.26 light-years, or roughly 3.086 x 10^13 kilometers (1.918 x 10^13 miles).
To determine the distance to a star in parsecs, astronomers measure the star’s parallax angle — the angular shift in the star’s position as seen from Earth six months apart — and use the formula: distance in parsecs = 1 divided by the parallax angle in arcseconds. Due to its origins and utility in measuring vast interstellar distances, the parsec is a fundamental unit in astrophysical and cosmological research.