Astronomical Unit Converter

About Astronomical Distance Units

The Astronomical Unit (AU) is a unit of length, roughly the distance from Earth to the Sun. It is defined by the International Astronomical Union (IAU) as exactly 149,597,870.7 kilometers. The AU is primarily used for measuring distances within our Solar System or around other stars.

A light-year (ly) is the distance that light travels in a vacuum in one Julian year (365.25 days). It is equivalent to about 9.461 trillion kilometers ($9.461 \times 10^{12}$ km) or approximately 63,241 AU. Light-years are commonly used to express distances to stars and other galaxies.

A parsec (pc) is defined as the distance at which one astronomical unit subtends an angle of one arcsecond. One parsec is equivalent to about 3.26156 light-years, approximately 206,265 AU, or about 30.857 trillion kilometers ($3.0857 \times 10^{13}$ km). Astronomers often prefer parsecs for larger distances, especially for galactic and extragalactic scales. Multiples like kiloparsecs (kpc), megaparsecs (Mpc), and gigaparsecs (Gpc) are used for successively larger distances.

• AU: Distances to planets, asteroids, comets within the Solar System (e.g., Jupiter is about 5.2 AU from the Sun).
• Light-years: Distances to nearby stars (e.g., Proxima Centauri is about 4.24 ly away), sizes of nebulae and star clusters.
• Parsecs (pc, kpc, Mpc, Gpc): Distances to more distant stars, structure of the Milky Way galaxy (kpc), distances between galaxies (Mpc), and large-scale structure of the Universe (Gpc).

• 1 AU ≈ $1.496 \times 10^8$ km
• 1 light-year (ly) ≈ 63,241 AU ≈ $9.461 \times 10^{12}$ km
• 1 parsec (pc) ≈ 206,265 AU ≈ 3.26 ly ≈ $3.086 \times 10^{13}$ km
• 1 kiloparsec (kpc) = 1,000 pc
• 1 megaparsec (Mpc) = 1,000,000 pc