What constants are used for the conversions?

The converter uses standard IAU-defined constants, where 1 AU is exactly 149,597,870,700 meters, and a light-year is the distance light travels in one Julian year.

How does the parallax helper calculate distance?

It uses the small-angle relationship where distance in parsecs (pc) equals 1 divided by the parallax angle in arcseconds (″).

Can I convert very large values using scientific notation?

Yes, you can check the scientific notation option to display results in exponential format.

What is the relationship between a parsec and a light-year?

One parsec (pc) is approximately equal to 3.26156 light-years (ly).

Does this tool support conversions back to meters and kilometers?

Yes, it converts any input unit into meters and kilometers alongside astronomical units.

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Astronomy

Light-Year and Astronomical Unit Converter

Convert between light-years (ly), parsecs (pc), astronomical units (AU), kilometers and meters using IAU-defined constants, with a parallax-angle → distance helper.

Details

What this tool helps you do

Convert cosmic distance scales and compute distance from stellar parallax. Units: ly, pc, AU, km, m. Parallax helper: d(pc) = 1 / π(arcsec).

Execution

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Prepared example runs

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2 examples

1 light-year to all units

Convert 1 ly to parsecs, AU, km and meters.

Proxima Centauri parallax → distance

Parallax 0.7685″ gives the distance to the nearest star.

<div class="ly-px-card">…parallax 0.7685″ → ~1.301 pc ≈ 4.244 ly…</div>

Inputs

Set the required fields, then run the tool.

5 options

ContentPaste or type the main input values.1

Parallax angle (arcsec) — optionaltextOptionalOptional: a stellar parallax angle in arcseconds. Returns distance in pc/ly/AU/km via d(pc) = 1/π(″).

SettingsAdjust formats, ranges, numbers, and modes.3

ValuenumberRequiredThe distance value to convert.From unitselectOptionalThe unit of the value you entered.Decimal placesnumberOptionalNumber of digits after the decimal point in the result.

TogglesEnable or disable optional behavior.1

Scientific notationcheckboxOptionalEnabled when checkedDisplay results in scientific (exponential) notation.

Result

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Samples

Light-Year and Astronomical Unit Converter

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Inputs

Result

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Key facts

Overview

When to use

How it works

Use cases

Examples

1. Converting Light-Years to Astronomical Units

2. Calculating Distance from Stellar Parallax

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