Space Unit Converter — AU, ly, pc, kpc, Mpc, km
Input & Units
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Results
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 | ≈ 3.26156 ly |
| 1 kpc | pc | 1,000 pc |
| 1 Mpc | pc | 1,000,000 pc |
Understanding Space Distance Units
When measuring the vast distances in space, everyday units like kilometers or miles quickly become impractical. Astronomers and cosmologists rely on specialized distance units designed for cosmic scales.
Kilometers (km)
A kilometer (km) is a standard metric unit of length, equal to 1,000 meters. While primarily used for terrestrial distances, it is also suitable for smaller astronomical scales—such as planetary diameters, distances to nearby moons, or the size of asteroids. For interplanetary and interstellar distances, however, larger astronomical units are far more practical.
Astronomical Unit (AU)
The astronomical unit (AU) is defined as the average distance between the Earth and the Sun—about 149,597,870.7 kilometers. This unit is commonly used for measuring distances within our Solar System, such as planetary orbits, the asteroid belt, or the distance to dwarf planets like Pluto.
Light-Year (ly)
A light-year (ly) is the distance that light travels in a vacuum in one Julian year (365.25 days). It is a measure of distance, not time. Light travels at roughly 299,792.458 kilometers per second, so one light-year equals about 9.461 trillion kilometers, or approximately 63,241 AU. Light-years are typically used for distances to nearby stars and interstellar objects.
Parsec (pc)
A parsec (pc), short for “parallax-second,” is the unit preferred by professional astronomers. It is defined as the distance at which one astronomical unit subtends an angle of one arcsecond. One parsec is approximately 3.26156 light-years or 206,265 AU. The parsec is closely tied to the trigonometric parallax method for measuring stellar distances. For larger scales, multiples are used:
- Kiloparsec (kpc): 1,000 parsecs; used for distances within galaxies (e.g., the size of the Milky Way).
- Megaparsec (Mpc): 1,000,000 parsecs; used for intergalactic distances, such as the spacing between galaxies in a cluster.
- Gigaparsec (Gpc): 1,000,000,000 parsecs; used for the largest measurable cosmological scales.
How This Tool Works
This space unit converter runs entirely in your browser, ensuring privacy and instant results. It uses fixed, precise conversion factors between all included units (AU, ly, pc, kpc, Mpc, km) to deliver accurate results as you type or change units. Outputs are rounded to a sensible number of significant figures for readability, and very large or very small values are shown in scientific notation.