Parallax Distance Calculator
Enter a star's annual parallax angle in arcseconds to find its distance in parsecs, light years and astronomical units using the parallax distance rule.
How to use the parallax distance calculator
- Enter the star's annual parallax angle in arcseconds.
- The tool takes one divided by the parallax to get parsecs.
- Read the distance in parsecs, light years and astronomical units.
Examples
A star with 0.1 arcsec parallax
parallax = 0.1 arcseconds
10 parsecs, about 32.6 light years
Alpha Centauri
parallax = 0.772 arcseconds
about 1.30 parsecs, 4.22 light years
Frequently asked questions
What is stellar parallax?
Parallax is the tiny shift in a nearby star's apparent position as Earth orbits the Sun. The closer the star, the larger the shift, so it reveals distance.
What is the parallax distance formula?
Distance in parsecs equals 1 divided by the parallax angle in arcseconds. A parallax of 0.5 arcseconds means a distance of 2 parsecs.
What is a parsec?
A parsec is the distance at which one astronomical unit subtends one arcsecond. It equals about 3.26 light years or 206,265 astronomical units.
Why use arcseconds for such small angles?
Even the nearest stars shift by under one arcsecond, so astronomers measure parallax in arcseconds and milliarcseconds to capture these tiny angles.
How far can parallax measure distance?
Parallax works best for nearby stars. Beyond a few thousand parsecs the angle gets too small to measure reliably, so other methods take over.
Related tools
Light Year Converter
Convert astronomical distances between light-years, AU, parsecs, kilometres, miles and metres. Fast, accurate unit conversion with worked examples. Free.
Escape Velocity Calculator
Calculate escape velocity from any planet, moon or star with v = sqrt(2GM/r). Pick Earth, Mars or Jupiter presets or enter mass and radius. Free tool.
Orbital Period Calculator
Calculate orbital period from Kepler's third law, T = 2 pi sqrt(a cubed / GM). Enter the semi-major axis and central mass to get seconds, days and years.
555 Timer Calculator
Calculate 555 timer astable frequency, period, high and low times and duty cycle from R1, R2 and the timing capacitor. Free oscillator design helper.
Absolute Humidity Calculator
Calculate absolute humidity in grams of water vapor per cubic meter from air temperature and relative humidity. Fast, free and works in your browser.
Allele Frequency Calculator
Find allele frequencies from genotype counts. Enter the number of AA, Aa and aa individuals to get the A and a allele frequencies and allele totals.