Stellar Parallax Distance Calculator
Calculate the distance to a star using its parallax angle.
Convert between parsecs, light-years, and AU instantly.
Stellar parallax is the tiny apparent shift in a star’s position as Earth orbits the Sun. By measuring this shift across six months (when Earth is on opposite sides of its orbit), astronomers can calculate the star’s distance.
The core formula:
d (parsecs) = 1 / p
Where p is the parallax angle in arcseconds (half the total apparent shift).
To convert to light-years or AU:
d (light-years) = 3.2616 / p
d (AU) = 206265 / p
What is a parsec? A parsec (pc) is the distance at which a star shows a parallax angle of exactly 1 arcsecond. It equals about 3.26 light-years or 206,265 AU β roughly 30.9 trillion kilometers.
Historical context: The method was first successfully used in 1838 by Friedrich Bessel to measure the distance to 61 Cygni. Ground-based telescopes can only reliably measure parallaxes for stars closer than about 100 parsecs. The ESA Hipparcos satellite extended this to roughly 1,000 parsecs.
The Gaia revolution: ESA’s Gaia mission (launched 2013) measures parallaxes with microarcsecond precision, extending reliable parallax distances to about 30,000 parsecs β covering a significant fraction of the Milky Way.
Reference star: Proxima Centauri (the nearest star to Earth) has a parallax of 0.7687 arcseconds, placing it at 1.295 parsecs (4.225 light-years). Smaller parallax = farther star. A parallax of 0.01 arcseconds means a distance of 100 parsecs.