Parallax Distance Calculator

Parallax is the small back-and-forth shift in a nearby star's apparent position as Earth moves from one side of its orbit to the other over six months. The annual parallax is half of that total swing. A closer star shifts more, so the size of the angle directly encodes distance.

Distance in parsecs equals 1 divided by the annual parallax in arcseconds, written d = 1 / p. This is not an approximation but the definition of the parsec, so a parallax of 0.5 arcseconds is exactly 2 parsecs and 0.1 arcseconds is exactly 10 parsecs.

A parsec is the distance at which one astronomical unit, the Earth to Sun distance, subtends an angle of one arcsecond. It works out to about 3.261564 light years or 206264.806 AU, which are the conversion factors this tool uses.

You enter the parallax in arcseconds. It returns parsecs and light years rounded to six decimal places and astronomical units rounded to four. Very large or very small results switch to scientific notation so they stay readable.

Divide by 1000 first, because the formula needs arcseconds. A modern satellite parallax of 5 milliarcseconds is 0.005 arcseconds, which gives 200 parsecs. Small parallaxes mean large distances, so keep an eye on the decimal point.

It is most reliable for nearby stars where the angle is comfortably above the measurement error. Ground telescopes reach a few hundred parsecs, and space missions like Gaia push to thousands of parsecs. Beyond that the angle shrinks below what can be resolved and other methods take over.

Distance is one divided by the angle, so a zero or negative parallax has no physical distance and the tool rejects it. In real surveys, noise can produce a tiny negative measured parallax, which simply means the star is too far for a usable reading.

No. The calculation isolates the annual parallax, the wobble caused by Earth's orbit. A star's steady proper motion across the sky and its motion toward or away from us are separate quantities and are not part of this distance rule.

Yes. The single division and the unit conversions run in your browser, so the parallax you type is never sent to a server and the page continues to work with no connection.