ucUnitCloudInternational unit matrix

Use case

Astronomy and hobby

Bring astronomical unit, light-year, parsec and light-second into one common length unit.

Working steps

  1. First decide which unit is the reference: au within the solar system, light-year for nearby stars, parsec at galactic scale.
  2. Convert the distance to kilometres when an everyday figure is needed.
  3. Use the light-second for signal travel times because it yields a time directly.
  4. When comparing sources check whether light travel time or distance is stated.
  5. Use the batch converter for several objects at once to sort orders of magnitude.

Checks

Unit family: Length

Matching conversions

Astronomical unit to KilometreAE → kmLengthKilometre to Astronomical unitkm → AELengthLight-year to KilometreLj → kmLengthParsec to Light-yearpc → LjLengthLight-year to ParsecLj → pcLengthLight-second to Kilometrels → kmLength

Further reading

TableAstronomical distancesGuideReading astronomical distances

Sources

IAU 2015 Resolution B2Defining constants for the astronomical unit, parsec and light-year.NIST CODATA fundamental physical constantsExact defining constants such as the speed of light in vacuum.
When not to use

Do not use as the sole basis for official, medical, safety-critical or contractual decisions.

Citation

Citation note: UnitCloud, use case, sources reviewed: September 2026. Source basis: IAU 2015 Resolution B2 · NIST CODATA fundamental physical constants.