Parallax Distance Calculator
Convert a star’s annual parallax angle into distance in parsecs, light-years and astronomical units.
How it works
d(pc) = 1 ÷ p(arcsec) · 1 pc = 3.2616 ly = 206,265 AU
As Earth orbits the Sun, a nearby star appears to shift slightly against the distant background over a year. Half that angular shift is the parallax p, and the distance in parsecs is simply its reciprocal in arcseconds — a parsec is by definition the distance at which parallax equals one arcsecond. Closer stars show larger parallax, so the smaller the angle, the farther the star.
Worked example
Proxima Centauri has a parallax of about 768.5 mas = 0.7685 arcsec. Distance = 1 ÷ 0.7685 ≈ 1.301 pc ≈ 4.24 light-years — the closest star to the Sun.
Sources: Parallax — Wikipedia
Frequently asked questions
What is a parsec?
A parsec is the distance at which one astronomical unit subtends an angle of one arcsecond — about 3.086×10¹⁶ m, or 3.2616 light-years. It comes directly from the parallax method.
Why is parallax measured in milliarcseconds?
Even the nearest stars have parallaxes below one arcsecond, and most are far smaller, so astronomers work in milliarcseconds (thousandths of an arcsecond). Missions like Gaia measure them to microarcsecond precision.
Does parallax work for very distant stars?
It becomes unreliable when the angle is smaller than measurement precision. Beyond a few thousand parsecs the parallax is too tiny to measure accurately, so other "standard candle" methods take over.
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This calculator is for educational purposes. Double-check important results before acting on them.