Sunlight’s commute
1 AU (Earth–Sun) is ~8 min 20 s at light speed — that’s 149,597,870.7 km or about 1.58×10⁻⁵ ly.
AU → ly
Astronomical Unit Converter and Astronomical Distance Converter
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Converted Result
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Common Astronomical Conversions
| From | To | Value |
|---|---|---|
| 1 AU | km | 149,597,870.7 km |
| 1 ly | km | 9,460,730,472,580.8 km |
| 1 pc | ly | 3.261563777 ly |
| 1 kpc | ly | 3,261.563777 ly |
| 1 Mpc | pc | 1,000,000 pc |
| 1 Gpc | Mpc | 1,000 Mpc |
| 1 AU | light-time | 8.316746 light-minutes |
Which Unit Should I Use?
km and meters
Best for spacecraft, planets, moons, asteroids, diameters, and engineering-scale distances.
Light-seconds and light-minutes
Best for signal delay and communication time across the Solar System.
AU
Best for Solar System orbit sizes, Earth-Sun scale, comet distances, and planet spacing.
ly
Best for public-facing interstellar distances such as nearby stars and nebulae.
pc and kpc
Best for astronomy catalogs, stellar parallax, star clusters, and galaxy structure.
Mpc and Gpc
Best for galaxy clusters, large-scale structure, and cosmology-scale maps.
Direct Pair Conversion Tables
Worked Examples
Constants and Methodology
Astronomical unit
1 AU = exactly 149,597,870,700 meters = 149,597,870.7 km. Source label: IAU 2012 Resolution B2.
Speed of light
c = exactly 299,792,458 m/s = 299,792.458 km/s. Light-time units are derived directly from this fixed value.
Julian year and light-year
1 Julian year = 365.25 days = 31,557,600 seconds, so 1 ly = c x 31,557,600 s = 9,460,730,472,580.8 km.
Parsec formula
1 pc = 648000 / pi AU = 30,856,775,814,913.67 km. kpc, Mpc, and Gpc are decimal multiples of parsecs.
Last reviewed: June 7, 2026. Updated: June 7, 2026. Constants checked against IAU/NASA reference conventions. This calculator converts fixed distance units only; it does not model live ephemerides, orbital mechanics, redshift, or relativistic travel time.
5 Fun Facts about Space Distances
What’s a parsec?
A parsec (pc) is the distance where 1 AU appears as 1 arcsecond: 206,265 AU ≈ 3.26156 ly ≈ 30.857 trillion km.
Parallax geometry
Milky Way size
Our galaxy’s stellar disk spans ~30 kpc — roughly 100,000 light-years across. Big neighborhood!
Galaxy scale
Nearest star check
Proxima Centauri is ~1.30 pc away — about 4.24 ly or ~268,000 AU beyond the Sun.
Closest neighbor
Mpc & expansion
On intergalactic maps, megaparsecs (Mpc) rule. A handy rule of thumb: galaxies recede ~70 km/s per Mpc (Hubble’s law).
Cosmic expansion
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Understanding Astronomical Distance Units
When measuring space distances, everyday units like meters, kilometers, and miles are useful near planets and spacecraft, while AU, light-years, parsecs, kpc, Mpc, and Gpc keep Solar System, stellar, galactic, and cosmological distances readable.
Meters, kilometers, and miles
Metric units are best for spacecraft operations, planet radii, moon distances, asteroid sizes, and public comparisons. Miles are included for readers using US customary distance examples.
Light-time units
Light-seconds, light-minutes, light-hours, and light-days convert distance into the time light takes to cross it in vacuum. They are distance units in this calculator, not clock durations for a moving spacecraft.
AU, lunar distance, and solar radii
The astronomical unit is a fixed length close to the Earth-Sun mean scale. Lunar distance uses the common mean Earth-Moon distance of 384,400 km. Solar radii use 695,700 km for scale comparisons near stars.
Light-years and parsecs
A light-year is the distance light travels in one Julian year. A parsec is defined geometrically from parallax: 1 pc = 648000 / pi AU. Kiloparsecs, megaparsecs, and gigaparsecs are decimal multiples for galaxy and cosmology work.
How this tool works
This astronomical distance converter runs entirely in your browser. It converts every input to kilometers using fixed constants, then converts from kilometers into the selected target unit and the all-units comparison table. Simple defaults keep results readable; the precision and scientific notation toggles expose more detail when needed.
Common Mistakes FAQ
Is a light-year a time unit?
No. A light-year is a distance. It equals how far light travels in vacuum during one Julian year, which is 9,460,730,472,580.8 km.
Why does 1 AU differ from the Earth-Sun distance on a given date?
The AU is now an exact fixed length. The real Earth-Sun distance changes through the year because Earth's orbit is elliptical, so a live ephemeris can report values slightly below or above 1 AU.
Why do parsec values differ slightly across sources?
Some tables round 1 pc to 206,265 AU or 3.26 ly. This calculator uses the defining formula 1 pc = 648000 / pi AU, so small differences usually come from rounding.
Should I use AU, ly, pc, kpc, Mpc, or Gpc?
Use AU inside the Solar System, light-years for public interstellar distances, parsecs for astronomy catalogs and parallax, kpc for galaxy structure, and Mpc or Gpc for extragalactic and cosmological scales.
Does this model orbit positions, redshift, or travel time?
No. It converts fixed distance units only. It does not model live planet positions, orbital mechanics, cosmological redshift, acceleration profiles, or relativistic travel time.