Space Unit Converter
Enter a value in any space unit, and see it instantly converted into all other common units.
Understanding Space Distance Units
When measuring the vast distances in space, everyday units like kilometers or miles are impractical. Astronomers and cosmologists use specialized units tailored to cosmic scales.
Kilometers (km)
A **Kilometer (km)** is a standard metric unit of length, equal to 1,000 meters. While commonly used for terrestrial distances, it can also be applied to smaller astronomical scales, such as the diameter of planets, distances to nearby moons, or the size of smaller asteroids. For larger cosmic distances, specialized units become more convenient due to the immense numbers involved.
Astronomical Unit (AU)
The **Astronomical Unit (AU)** is defined as the average distance between the Earth and the Sun. It's approximately 149.59787 million kilometers. This unit is primarily used for distances within our solar system, such as the orbits of planets or the dimensions of asteroid belts.
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 unit of distance, not time. Light travels at approximately 299,792.458 kilometers per second. One light-year is roughly 9.461 trillion kilometers or about 63,241 AU. Light-years are commonly used for interstellar distances, such as the distances to nearby stars.
Parsec (pc)
The **Parsec (pc)**, short for "parallax-second," is the unit preferred by professional astronomers. It is defined as the distance at which one astronomical unit (AU) subtends an angle of one arcsecond. One parsec is approximately 3.26156 light-years or 206,265 AU. Its definition is directly related to the trigonometric parallax method used to measure stellar distances. For larger scales, multiples are used:
- **Kiloparsec (kpc):** 1,000 parsecs, used for distances within a galaxy (e.g., the size of the Milky Way).
- **Megaparsec (Mpc):** 1,000,000 parsecs, used for intergalactic distances and the scale of the observable universe (e.g., distances to other galaxies or galaxy clusters).
- **Gigaparsec (Gpc):** 1,000,000,000 parsecs, for the very largest cosmological scales.
How This Tool Works
This converter operates entirely client-side, ensuring your privacy. It uses fixed conversion factors between these astronomical units to provide instant results as you type or select a unit. The values are rounded to a reasonable number of significant figures for clarity.