Parallax Distance Calculator
Stellar parallax is the most fundamental distance measurement in astronomy. As Earth orbits the Sun, nearby stars appear to shift slightly against the background of distant stars. The parallax angle p (half of the total annual shift) in arcseconds gives the distance immediately: d = 1/p parsecs. This direct geometric method requires no assumptions about stellar physics, making it the foundation of the entire distance ladder. Enter a parallax angle in arcseconds to compute the distance in parsecs, light-years, and astronomical units.
Parallax distance formula
d (parsecs) = 1 / p (arcseconds)
1 parsec = 3.2616 light-years = 206,265 AU
The formula is exact by the definition of the parsec. A star with p = 0.5 arcsec is 2 parsecs away. A star with p = 0.01 arcsec (1 milliarcsecond) is 100 parsecs away, at the limit of ground-based astrometry. Gaia can measure parallaxes to about 7 microarcseconds, allowing distances to roughly 10 kiloparsecs.
Parallax of nearby stars
Proxima Centauri: p = 0.7685 arcsec, d = 1.30 pc (4.24 ly). Alpha Centauri A/B: p = 0.7421 arcsec, d = 1.35 pc (4.40 ly). Barnard's Star: p = 0.5476 arcsec, d = 1.83 pc (5.96 ly). Sirius: p = 0.3791 arcsec, d = 2.64 pc (8.60 ly). The Pleiades cluster: p = approximately 0.00716 arcsec, d = 140 pc (456 ly).
Parallax distance: frequently asked questions
What is stellar parallax?
Stellar parallax is the apparent shift in a nearby star's position against the background of distant stars as Earth moves from one side of its orbit to the other (a baseline of 2 AU over 6 months). The parallax angle p is half of this total shift, measured in arcseconds.
What is the definition of a parsec?
A parsec is defined as the distance at which a star shows a parallax of exactly 1 arcsecond. So d(parsecs) = 1/p(arcseconds). One parsec = 206,265 AU = 3.0857 x 10 to the 16th meters = 3.2616 light-years.
What is the parallax of Proxima Centauri?
Proxima Centauri has a parallax of 0.7685 arcseconds, giving a distance of 1/0.7685 = 1.301 parsecs = 4.243 light-years. This is the nearest star to the Sun. The Hipparcos satellite measured this; the Gaia mission has since improved the precision.
What is the maximum distance measurable by parallax?
From the ground, parallax measurements are reliable to about 100 parsecs (parallax of 0.01 arcseconds). The Hipparcos satellite extended this to about 1,000 parsecs. The Gaia mission achieves microarcsecond precision, allowing parallax distances out to several kiloparsecs.
Why can parallax only measure nearby stars?
For distant stars, the parallax angle becomes too small to measure accurately. At 1,000 parsecs, the parallax is only 0.001 arcseconds (1 milliarcsecond). Atmospheric turbulence limits ground-based accuracy to about 0.01 arcseconds, though space-based missions like Gaia achieve far better precision.
Official sources
- ESA Gaia mission data: cosmos.esa.int/web/gaia.
- USNO SIMBAD and the Hipparcos catalog: aa.usno.navy.mil.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.