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Stellar Parallax Distance Calculator

Find a star's distance in parsecs, light-years, and astronomical units from its measured parallax angle, using the defining relationship d(pc) = 1 / p(arcsec).

Distance (parsecs)
1.3009
Distance (light-years)
4.243
Distance (AU)
268,329

How it works

Stellar parallax is the tiny apparent shift in a nearby star's position against the distant background stars, seen from opposite sides of Earth's orbit six months apart. The parsec (short for 'parallax of one arcsecond') is defined so that a star showing exactly 1 arcsecond of parallax sits exactly 1 parsec away, which makes the distance formula elegantly simple: distance in parsecs = 1 ÷ parallax angle in arcseconds — no trigonometry needed once the angle is in arcseconds.

That parsec figure is then converted to two more familiar units: light-years, using the fixed conversion 1 parsec = 3.261563 light-years, and astronomical units (Earth-Sun distances), using 1 parsec = 206,264.806 AU — the exact number of AU at which a 1 AU baseline subtends an angle of 1 arcsecond.

The default value, 0.7687 arcseconds, is Proxima Centauri's real measured parallax, the nearest known star to the Sun — plugging it in recovers its well-known distance of roughly 4.24 light-years.

FAQ

Why does a smaller parallax angle mean a larger distance?

Because the two are inversely related by definition (distance = 1 ÷ parallax) — a star that barely appears to shift at all as Earth orbits the Sun must be extremely far away, while a relatively large apparent shift means the star is comparatively close. This is also why parallax can only measure the distance to relatively nearby stars: beyond a few thousand light-years the angle becomes too small for even space telescopes to measure reliably.

Is this the same method real astronomers use?

Yes — trigonometric parallax is considered the most direct and reliable way to measure stellar distances, and it's the technique missions like ESA's Gaia use to measure the distances (and parallax angles) of over a billion stars. This calculator applies the exact same defining formula those measurements are converted with.

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