Convert length and distance units — meters, feet, inches, kilometers, miles, light years and more.
| Unit | Name | Value |
|---|---|---|
| 0.001 au | 1.58123e-08 ly | |
| 0.01 au | 1.58123e-07 ly | |
| 0.1 au | 1.58123e-06 ly | |
| 1 au | 1.58123e-05 ly | |
| 5 au | 7.90614e-05 ly | |
| 10 au | 0.000158123 ly | |
| 50 au | 0.000790614 ly | |
| 100 au | 0.00158123 ly | |
| 1000 au | 0.0158123 ly |
Multiply the number of Astronomical Units by 1.58123e-05 to get Light Years. Formula: ly = au × 1.58123e-05. Example: 10 au × 1.58123e-05 = 0.000158123 ly. To reverse, divide Light Years by 1.58123e-05 to get Astronomical Units.
| Astronomical Unit (au) | Light Year (ly) |
|---|---|
| 0.001 au | 1.5812×10-8 ly |
| 0.01 au | 1.58123e-07 ly |
| 0.1 au | 1.58123e-06 ly |
| 0.5 au | 7.90614e-06 ly |
| 1 au | 1.58123e-05 ly |
| 2 au | 3.16246e-05 ly |
| 5 au | 7.90614e-05 ly |
| 10 au | 0.000158123 ly |
| 20 au | 0.000316246 ly |
| 50 au | 0.000790614 ly |
| 100 au | 0.00158123 ly |
| 250 au | 0.00395307 ly |
| 500 au | 0.00790614 ly |
| 1000 au | 0.0158123 ly |
| 10000 au | 0.158123 ly |
To convert Astronomical Unit to Light Year, multiply by 1.58123e-05. Example: 10 au = 0.000158123 ly
To convert Light Year back to Astronomical Unit, divide by 1.58123e-05 (multiply by 63242). Use the swap button above.
Start with 100 Astronomical Units = 0.00158123 ly as your reference point. Scale up or down from there.
Astronomers describing nearby stars use light-years for public communication (Proxima Centauri: 4.24 ly = 268,000 AU), converting between units when switching between solar system and stellar contexts.
Exoplanet researchers describe orbital distances in AU (Earth-equivalent orbits: ~1 AU), then express the distance to the host star system in light-years for the observational and travel-time context.
Engineers designing hypothetical interstellar probes like Breakthrough Starshot express target star distances in light-years, then convert to AU for comparison with known solar system scales and mission scope.
Galactic astronomers describing the Milky Way's structure use light-years for large-scale features (galaxy diameter: ~100,000 ly) while AU describes the scale of individual planetary systems within it.
Science journalists convert between AU and light-years when explaining cosmic distances — "the Oort Cloud extends to 100,000 AU, which is about 1.6 light-years from the Sun" bridges solar system and stellar scales.
Physics educators use AU-to-light-year conversion to help students understand the hierarchy of cosmic scales — from planetary orbits (AU) to stellar distances (light-years) to galactic (kiloparsecs).
The Astronomical Unit is a unit of Length measurement (symbol: au). 1 au = 1.58123e-05 ly. Used in scientific and practical Length measurement applications.
The Light Year is a unit of Length measurement (symbol: ly). It is part of an internationally recognised measurement system used alongside the Astronomical Unit.
The astronomical unit has ancient roots — Aristarchus of Samos attempted to measure the Earth-Sun distance around 270 BC, estimating it at 18–20 lunar distances (the true value is about 390). For centuries the AU was estimated using Venus transit observations and trigonometry. Edmond Halley organised the first coordinated international transit-of-Venus expedition in 1716. The modern value was determined by radar ranging to Venus in 1961. The IAU formally defined the AU as exactly 149,597,870,700 metres in 2012 — a fixed constant of physics, not a measured distance.
The light-year was not coined by professional astronomers — it first appeared in a German publication in 1851 written by Otto Ule as a way to make stellar distances comprehensible to general audiences. It equals the distance light travels in one Julian year: exactly 9,460,730,472,580.8 kilometres. Professional astronomers often prefer parsecs, but the light-year became the public's unit of choice for cosmic distance because it connects speed with scale. One light-year equals about 63,241 astronomical units.
Common use: Astronomical Unit to Light Year conversion is needed when working with international standards, scientific publications, or reference materials that use different unit systems for Length measurement.