Parallax Calculator

Stellar parallax is the apparent shift in the position of a nearby star against the background of distant stars, as seen from Earth at different points in its orbit around the Sun. By measuring this tiny angular shift, astronomers can calculate how far away the star is. The larger the parallax angle, the closer the star.

The parallax angle is half the total angular shift of a star observed from opposite sides of Earth's orbit (a baseline of 2 AU). It is measured in arcseconds — one arcsecond being 1/3600 of a degree. For most stars, this angle is extremely small, often measured in milliarcseconds or microarcseconds.

Use the formula D = 1 / P, where D is the distance in parsecs and P is the parallax angle in arcseconds. For example, if a star has a parallax of 0.5 arcseconds, its distance is 1 / 0.5 = 2 parsecs. To convert parsecs to light-years, multiply by 3.2616.

A parsec (pc) is the distance at which a star would have a parallax angle of exactly 1 arcsecond. It equals approximately 3.2616 light-years or 206,265 astronomical units. Parsecs are the natural unit for the parallax formula, which is why astronomers prefer them for stellar distance measurements.

The stellar parallax method is only effective for relatively nearby stars — generally within a few thousand parsecs. For very distant stars, the parallax angle becomes too small to measure accurately, even with modern instruments. Ground-based telescopes can reliably measure parallax angles down to about 0.01 arcseconds, while space missions like Hipparcos and Gaia have extended this to microarcsecond precision.

Proxima Centauri, the nearest star to Earth besides the Sun, has a parallax angle of approximately 768.5 milliarcseconds (0.7685 arcseconds). This corresponds to a distance of about 1.30 parsecs or 4.24 light-years.

1 arcsecond (arcsec) = 1000 milliarcseconds (mas) = 1,000,000 microarcseconds (μas). Most nearby bright stars have parallaxes measured in milliarcseconds. Space observatories like Gaia measure parallaxes in microarcseconds, enabling distance measurements to stars thousands of parsecs away.

Yes — simply switch the mode to 'Parallax from Distance', enter the known distance in parsecs, light-years, or astronomical units, and the calculator will return the corresponding parallax angle in arcseconds and milliarcseconds using the inverse formula P = 1 / D (where D is in parsecs).