Parallax Calculator

Measuring Distance with Parallax

Parallax is the apparent shift of a nearby object against a distant background when the observer changes position. Astronomers use stellar parallax to estimate distances to nearby stars.

Stellar Parallax Formula

$$d\ (\text{pc}) = \frac{1}{p\ (\text{arcsec})}$$

One parsec is defined as the distance at which one astronomical unit subtends one arcsecond of parallax.

Baseline Parallax Formula

$$d = \frac{b}{2 \tan(p/2)}$$

Here $b$ is the baseline between observation points and $p$ is the parallax angle. This form is useful for surveying and short-baseline geometry.

Related tools: Astronomical Converter and Hubble's Law Calculator.

Frequently Asked Questions

What is a parsec in everyday terms?

One parsec is about 3.26 light-years, or roughly 30.9 trillion kilometers.

Why must parallax angle be in arcseconds for d = 1/p?

That definition is built into the parsec unit. Convert degrees or arcminutes to arcseconds first if needed.

What baseline does stellar parallax use?

Earth's orbit provides about 2 AU baseline between observations six months apart.

When should I use the baseline formula?

Use it when you know a physical baseline and measured parallax angle in a local geometry problem.

Can parallax measure very distant galaxies?

Stellar parallax works for relatively nearby stars. Extremely distant objects need other distance indicators.

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Measuring Distance with Parallax

Stellar Parallax Formula

Baseline Parallax Formula

Frequently Asked Questions

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