Parallax Distance Calculator: d = 1 / p

How far away a star is, from how much it seems to shift against the background.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose which quantity you want to find.

Enter the other values in the units shown.

The calculator gives the answer with the formula, the substituted numbers, and the answer in other units.

Formulas used

  • d = \frac{1}{p}
  • p = \frac{1}{d}

Worked example

With the default numbers in the calculator above:

  1. The formula, arranged to find the distance: distance = (1) / (parallax angle)
  2. Put the values in (every value in its SI unit): distance = (1) / (0.7687)
  3. The answer: distance: 1.3009 parsecs
  4. The same answer in other units: 4.24296 light years

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What is a parsec?

The distance at which a star would have a parallax of one arcsecond. It is 3.26 light years.

How far away is Proxima Centauri?

About 1.30 parsecs, which is 4.24 light years.

Why six months apart?

The Earth is on opposite sides of its orbit then, so the star shifts by the biggest amount.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any astronomy text (stellar parallax).

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